No one seems to agree. Should the electrical system be bonded to the hull or not?
Earthing in a marine installation
How should earthing arrangements be made on a boat?
This is one of the most common questions asked and one of the most misunderstood subjects in the field. Even so called "experts" very often get it completely wrong.
The subject is also, unfortunately, one of the most complicated to answer. Consequently this document is rather long.
The complexity problems arise because there are so many separate, unrelated, aspects to consider. In order of priority they are........
1. The matter of safety for those on board and for those not on board. The matter of safety for those not onboard is often overlooked or completely disregarded by the uninitiated.
2. The matter of galvanic corrosion.
3. The reliability of the equipment on board.
Now there are two ways we can answer this question. Some people will not believe a technical argument, perhaps because they don't understand it, perhaps because their interpretation of technical matters is incorrect. And for those people we will answer the question like this:-
The AC electrical system earth should be bonded to the hull because:-
1. The European Recreational Craft Directive says so.
2. The British Marine Electronics Association "Code of Practice" says so.
3. The book "The Boatowners Electrical and Mechanical Manual" by Nigel Calder (a world renowned expert) says so.
4. The ABYC (American Boat and Yacht Council) recommends so.
How many more references do you need?
The above people and organisation didn't come to the conclusion that the ground should be bonded to the hull on a whim. They came to this conclusion because they spent a lot of time and effort studying every possible fault and condition and drawing the conclusion that to bond the ground to the hull is, on balance, far safer than to leave the system floating.
The other way to answer the question is like this:-
Let's tackle the matter of safety for those on board and those not on board first.
The first safety matter is obviously that of electric shock. Clearly we have to reduce the risk of this as much as possible.
Electrical equipment is manufactured to 2 distinct standards. "Single insulated" (Class I) and "double insulated" (Class II).
"Single insulated" equipment is manufactured in such a way that the AC mains electricity is insulated from the casing so that the two do not touch. In the event of an internal fault, this may no longer be the case. For instance a live cable, inside the equipment, may become loose and contact the case of the equipment. This obviously presents a shock hazard if the equipment casing is metal. So the casing is earthed to the green/yellow conductor in the power cord.
In the event of the fault described above, the live cable connects to the case of the equipment, which is connected to the earth conductor, which causes an enormous current to flow, which blows the incoming fuse thus interrupting the supply.
That is the safety mechanism of single insulated equipment.
You will instantly see that the integrity of the earth conductor is vital to the safety of the equipment.
"Double insulated" equipment is manufactured in such a way that even if the same internal fault arises, the cable simply cannot contact anything metal that is accessible from the outside of the equipment. So even if the live conductor becomes detatched inside the equipment, it does not present a shock hazard to the user. "Double insulated" equipment, by definition, has two insulation barriers between the electrical parts and the user. This usually consists of the insulation on the cables and connections inside the equipment as the first barrier, then an insulating case as the second barrier. This equipment usually consists of an entirely non conductive outer casing (i.e. plastic).
"Double insulated" equipment does not require an earth conductor in the power cord.
These are the two accepted standards throughout Europe (and most of the rest of the world) for safety in AC powered equipment.
"Double insulated" still suffers from the problem that the equipment can still cause an electric shock if it gets wet and the water gets to the insides of the equipment. This danger cannot arise with "single insulated" equipment as the casing is "held" at the same voltage as the ground upon which we stand by the earth conductor in the power cord. Therefore no voltage difference can appear between the case of the equipment and the ground. Therefore no current can flow through someone holding the equipment and stood on the ground.
A vessel with AC and shorepower facilities
If we now take a look at a boat (let's take a metal hulled boat for this purpose), plugged into shorepower, we can instantly see that, from the point of view of someone not on the boat it is a piece of equipment on the end of a power cord. We can further see that it is a "single insulated" piece of equipment and therefore must have it's casing (the hull) connected to the ground conductor in order to ensure the safety of those outside the equipment (the vessel).
If the hull is not connected to the ground conductor, and we get the fault of a loose live cable touching the hull, we get the situation where the hull is at 230 volts (in Europe) and the ground around it is at 0 volts. It obviously depends upon the conductivity of the water (whether fresh or salt water, pollution levels etc) but it is far from certain (particularly in fresh water) that this fault will cause sufficient current to blow the fuse on the shorepower point.
Anyone touching the boat and the ground (perhaps climbing aboard) will instantly receive an electric shock.
Anyone (or anything) swimming in the water will have an enormous voltage differential presented across their body which may be sufficient to electrocute them, and even if not, will almost certainly paralyse them causing them to drown.
This fact cannot be argued against. The hull must be bonded to the incoming earth conductor in order to ensure the safety of those not on board the vessel.
And I really think this is the crux of the matter. When the safety of those not on the vessel is considered there is no argument whatsoever for not bonding the ground to the hull. It is that simple.
Now it could be argued that the presence of a Residial Current Device will sense this fault and trip thereby ensuring the safety of everyone in the vicinity of the vessel however there are a couple of problems here that means this cannot be relied upon.
Firstly, RCDs are not manadatory in many parts of the world (including the UK), so there may not actually be one fitted.
Secondly, even if one is fitted, whilst it is almost certain that it will trip in salt water, this is not the case in fresh water (because freshwater is a much poorer conductor than salt water). Especially on a small boat, or one with most of the underwater steelwork painted, or a GRP or wooden boat with some underwater metalwork.
Many people argue that the AC system should not be bonded to the earth conductor (for the reason that it can cause galvanic corrosion problems which we will come to later), but when presented with the above scenario, hold their head in shame and admit that it is something they had never even considered. They had only considered the safety of those on board the vessel.
That one argument alone confirms that, in the case of a vessel that has the facility to use shorepower, the AC ground must be bonded to the hull. To not bond them is leaving oneself open to electrocution of people (perhaps oneself or one's own family), sleepless nights in the event it should happen, litigation and possibly even criminal proceedings for manslaughter for ignoring all the codes of practice, guidlines and actual laws which state, quite categorically, that they should be bonded.
A vessel with an AC system but no facilities to use shorepower
The power in this case would come from either a generator or an inverter. It is still 230 volt (in Europe) power, it is just as dangerous as shorepower.
However in this case the risk to those not on board does not exist.
There are many possible causes of electric shock, the most common being someone touching live and earth at the same time. Now in the case of a generator or inverter, if the system is totally isolated from the hull (which we can do in this case as the risk to those not on board no longer exists) this danger no longer exists.
However, if the system is totally isolated from the hull, and a fault arises that connects live to the hull somewhere in the installation, no resultant problem will ensue. The system will continue to operate perfectly...... until someone touches the hull (which is at 230 volts) and the case of a "single insulated" piece of equipment (which is at 0 volts) at the same time. They will receive an electric shock.
Had the AC system had it's earth conductor bonded to the hull this situation could not arise because as soon as the live cable touched the hull either the fuse would blow or the inverter or generator would cut-out having detected an overload.
Now in order to ensure full safety, we need to also bond neutral and earth at the output of the inverter and/or generator and install RCCDs on the outputs of the inverter and/or generator.
Either way, we still need to bond the AC system to the hull.
AC in general
So whether the system can use shorepower or not, if we have AC on board, the earth conductor must be bonded to the hull.
DC system with no AC on board
From the point of view of safety it makes no difference whether or not the DC system is bonded to the hull.
From the point of view of galvanic corrosion it makes no difference whether or not the DC system is bonded to the hull (but the hull must never be used as a return path in the manner of vehicle wiring).
However, if the DC positive side is bonded to the hull this can have huge implications for galvanic corrosoion.
Remember, the most positive (voltage wise) point will be the point that erodes. The negative point will receive a plating from the most positive point.
This diagram shows a single battery, with the negative side bonded to the hull. It also shows a load switch, a load and two areas of dampness represented by the lines with arrowheads at each end.
No current will flow through the damp area at A as both ends are held at the same voltage by the bonding to the hull.
Current will flow through the damp area at B and, due to electrolysis, the wire will erode (as it is more positive) and plate the section of the hull at B (which is more negative) with a small amount of copper.
This diagram shows exactly the same installation but this time the positive side has been bonded to the hull.
This time no current will flow through the damp area at B because both ends are held at the same voltage by the bonding to the hull.
Current flows through the damp area at A, but this time the hull will be eroded (as it is more positive) and plate the wire (as it is more negative) with a small amount of steel from area A.This is stray current erosion. The hull is being eaten away. Purely and simply by bonding the positive to the hull instead of bonding the negative.
If the DC system is not bonded to the hull at all then obviously this cannot happen.
However, if the positive becomes bonded as a result of a fault (a frayed wire perhaps), the system will continue to operate, the fault will not show itself with any symptoms. So the vessel now has a positive bonded system without the owner knowing anything about it. And with it, the vessel also has all the problems of a positive bonded DC system - i.e. greatly accelerated stray current erosion.
There are two options to protect against this....
1. Bond the negative to the hull. If a fault occurs that attempts to bond the positive to the hull, the main fuse will blow, alerting the owner to the problem.
2. Keep the system isolated from the hull and fit a device that detects if the positive somehow becomes bonded to the hull. I am not aware of any such device and do not see a market big enough to warrant designing one.
So even with a DC system and no AC system, bonding the DC system to the hull is still required. Without doing so, you may find you have inadvertently created a positive grounded system.
AC system and DC system
If both electrical systems are installed then all of the above applies. i.e. it is imperative that both systems be bonded to the hull.
There is also another scenario in this case to further convince the doubters.
Assume the AC system is bonded to the hull but the DC system is not.
Some equipment is connected to both systems. This sounds rare - in actual fact it isn't, dual voltage fridges, battery chargers and inverters are all connected to both systems.
A fault in one of these items could cause AC mains to be presented to the DC side. If both systems are bonded to the hull, this will instantly cause the incoming fuses or circuit breakers to blow.
If one of the systems is isolated from the hull this will not happen. The result will be that the DC system (which we all assume is safe to touch, and which usually has components with insulation rated for about 50 volts) will be set at 230 volts with respect to the hull or the other electrical system. Clearly this is highly dangerous.
In summary, whatever electrical system is fitted, it is imperative that the system is bonded to the hull.
Galvanic corrosion problems as a result of bonding the AC system to the hull
When plugged into shorepower, and the AC system ground is bonded to the hull, the quayside, other boats and your boat creates a battery which, 9 times out of ten, causes a current to flow in such a direction that your hull erodes. This is galvanic erosion.
There are 2 simple remedies to this problem. One is to fit an isolation transformer, the other is to fit a galvanic isolator. Both will cure the problem.
Bonding the DC system cannot affect this.
All bonding should be done at one central point. It is not acceptable to bond various parts of the system in various separate places. This can cause voltage differentials between various parts of the hull which can lead to stray current erosion.
Finally, a few people with steel hulled narrowboats have mentioned that the resistance between the hull (which is usually almost completely bare steel in a narrowboat) and the actual ground (of the world) is so low (even in fresh water) that an RCD will always trip in the event of a live-earth fault and in fact some have gone on to say that the resistance is so low that a main circuit breaker or fuse will blow.
We accept that this is true most of the time however there are narrowboats out there which have completely or almost completely painted hulls and in this case is it far from certain that an RCD or circuit breaker will blow.
Further, narrowboat owners seem to forget that not all boats have steel hulls. Many are fibreglass or wooden. Some are carbon composite etc. One has to think further afield than "my boat". These regulations and guidelines have to cover all boats not just one or two!
There is a further discusion of galvanic corrosion here.
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http://gilwellbear.wordpress.com/2013/08/11/galvanic-currents-and-zincs/
Galvanic Currents and “Zincs”
“Galvanic Corrosion” is a very complicated topic. Galvanic corrosion is a normal, predictable and unwanted electro-chemical phenomenon. The subject of Galvanic Corrosion spans the sciences of electricity, chemistry, physics and an entire body of engineering study. There are at least four ABYC Standards that relate to it:
- A28, “Galvanic Isolators,” July, 2008,
- E2, “Cathodic Protection,” July, 2013,
- E11, “AC and DC Electrical Systems on Boats,” July, 2012, and
- TE4, “Lightening Protection.” July, 2006.
This post is written as a high-level introduction to the key terms and concepts of Galvanic Corrosion. It is written for boaters and others who have little or no prior electrical background. In struggling with the technical concepts and unfamiliar terminology used to describe them, one may find that skilled people slip almost casually from one contextual use of terms to another. For beginners and bystanders, that can be confusing and frustrating. My hope is this post will wrap some perspective and understanding around the topic.
In any discussion of “Galvanic Corrosion,” there are two inescapable and frequently-encountered terms one must understand. The noun-forms are “anode” and “cathode.” The adjective-forms are “anodic” and “cathodic.” These terms are always used in a particular context. The context will either be a description of:
- a specific atomic characteristic of an individual metal; i.e., its “Galvanic Potential” on a “Galvanic Series of Metals,” or a “Nobility Scale,” or
- the relative relationship of one metal to another on a “Galvanic Series of Metals,” or a “Nobility Scale,” or
- the electrical polarity of a active energizing device (usually a battery) or an externally energized attached device.
The concepts these terms represent are fundamental to understanding galvanic corrosion.
Relative to any “Galvanic Series,” or “Nobility Scale,” “cathodic” metals are highly “noble,” or “passive metals.” They are electrically negative. They are greatly resistant to galvanic corrosion. Examples include titanium, gold and graphite. “Anodic” metals are “less noble,” or “active” metals. They are electrically positive. They are moderately to highly subject to galvanic corrosion. Examples with which all boaters are familiar include magnesium, aluminum and zinc, all used as “sacrificial anodes” on boats.
As an example of the three cases, above, consider the three metals, 316 Stainless Steel (passive), bronze and zinc. 316SS (passive; i.e., in free-circulating sea water) is strongly cathodic, with a galvanic potential around -0.05. Bronze is mid-range on the Galvanic Series with a galvanic potential of -0.31. Zinc is strongly anodic, with a galvanic potential of about -1.05. These numbers come from the table later in the post. What I want to highlight here is that so far in this paragraph, the context has been the metal-specific galvanic electrical characteristic, as in context case #1, above. However, I can also say that bronze is anodic when compared to 316 SS, and cathodic when compared to zinc. Here, we are not talking about the metal-specific characteristic of bronze, but rather it’s relative galvanic potential compared to another metal, as in context case #2 above. The point is, in one context bronze may be referenced as a cathodic metal and in a second context be referenced as anodic metal. So, listeners, listen carefully for context.
Metals incur galvanic corrosion only when they are in contact with other metals. Therefore, galvanic corrosion should always be thought of in the context of a pair of metals. The common terminology is of a “joined pair,” or a “couple,” of metals.
For “Galvanic Corrosion” to occur, three conditions are necessary:
- Metals must be “well separated” on the “Galvanic Series:”
The larger the galvanic potential difference between the metals involved, the greater the probability of galvanic corrosion, and the faster that corrosion will progress. A small difference is unlikely to become an issue.
- The metals must be electrically connected together:
The metals can be pressed together, riveted, bolted, welded, clamped, or even piled-upon each other.
- Both metals must be immersed in an “electrolyte:”
An electrolyte is an electrically conductive medium. The electrolytic medium acts to complete the electrical circuit. If the conductivity of the medium is high, the metal-to-metal corrosion of the less noble metal will be dispersed over a larger area. If the conductivity of the electrolytic medium is low, the corrosion will be localized to the part of the less noble metal nearest to the mechanical connection between the metals. Sea water is an excellent electrolyte, brackish water, less, fresh water, not so much.
When all of these conditions are met, a difference in “galvanic potential” (a voltage) exists between the different metals in the electrolyte solution. That voltage is the driving force for electrons to flow from one metal to the other metal through the electrolyte. This current results in deterioration of one of the metals. Inside a battery, when one metal is fully depleted, the battery is thought of as “dead.” Between metals in any mechanical system, it’s thought of as “destructive galvanic corrosion.” When the boat floating in the water is, itself, the battery, it’s both.
A unique “galvanic series” is associated with each particular electrolyte solution. Therefore, across the study of metallurgy and corrosion science, variances in galvanic series will be found depending upon the composition of the specific electrolytic solution. The sea water galvanic series is a very complete compendium, and also just happens to apply to us as boaters.
The following table shows galvanic potentials of many common metals in free-flowing sea water at ambient temperature:
| Galvanic Series In Flowing Sea Water | |
| Material | Steady State Electrode Potential, Volts (Saturated Calumel Half-Cell) |
| Graphite | +0.25 |
| Platinum | +0.15 |
| Zirconium | -0.04 |
| Type 316 Stainless Steel (Passive) | -0.05 |
| Type 304 Stainless Steel (Passive) | -0.08 |
| Monel 400 | -0.08 |
| Hastelloy C | -0.08 |
| Titanium | -0.1 |
| Silver | -0.13 |
| Type 410 Stainless Steel (Passive) | -0.15 |
| Type 316 Stainless Steel (Active) | -0.18 |
| Nickel | -0.2 |
| Type 430 Stainless Steel (Passive) | -0.22 |
| Copper Alloy 715 (70-30 Cupro-Nickel) | -0.25 |
| Copper Alloy 706 (90-10 Cupro-Nickel) | -0.28 |
| Copper Alloy 443 (Admiralty Brass) | -0.29 |
| G Bronze | -0.31 |
| Copper Alloy 687 (Aluminum Brass) | -0.32 |
| Copper | -0.36 |
| Alloy 464 (Naval Rolled Brass) | -0.4 |
| Type 410 Stainless Steel (Active) | -0.52 |
| Type 304 Stainless Steel (Active) | -0.53 |
| Type 430 Stainless Steel (Active) | -0.57 |
| Carbon Steel | -0.61 |
| Cast Iron | -0.61 |
| Aluminum 3003-H | -0.79 |
| Zinc | -1.03 |
| Data from ASM Handbook, Vol. 13, p. 675. | |
Your boat, when in the water, is a natural battery (a “galvanic cell”). That natural battery produces a very small DC voltage between its under-water “cathodic” and “anodic” metals. The water in which the boat is floating is the necessary “electrolyte” in this natural battery (galvanic cell), and the dissimilar metals of the propeller, drive shaft, reduction gear/transmission, rudder, thruster components, outdrives, trim tabs, thru-hulls, radio ground plane, speed and sounder sensor bodies, etc., etc., etc., are the relatively anodic (+) and relatively cathodic (-) terminals of the battery.
Electrons carry a negative electrical charge. Galvanic electric currents consist of a “flow of electrons” out of, and back into, the galvanic cell created by your boat. The electrons begin their journey at the under-water cathodic (-) metals of the boat, flow through the water and into the seabed, find their way through the earth to the ground rod of the shore power electrical system, flow through the shore power earth/ground infrastructure to the AC safety ground of your dock, flow back onto the boat through the boat’s shore power safety ground conductor, flow into and through the boat’s bonding system, and finally arrive back at the under-water anodic (+) metals of the boat. In the process, these small DC currents erode and deteriorate the material of the least “noble” metals they encounter. Hopefully, that will be sacrificial anodes (zincs) and not the more noble metals of props, outdrives, transmissions, rudders, thrusters, etc.
The galvanic potential (voltage) that causes the above flow of electrons is determined by the specific cathodic and anodic metals involved and a variety of other factors related to the composition of the electrolyte. The flow of electrons from a cathodic metal leaves behind a slight positive charge. To balance that charge, anodic metal ions are shed into the electrolyte. That shedding is the deterioration we see with sacrificial anodes (zincs). This process can be thought of as similar to electroplating.
If you aren’t familiar with this language and these advanced electrical and materials concepts, you are in the clear majority of people and boaters! Frankly, only true, insanely devoted electrical geeks venture into these “techno-weeds!” Most electrical service professionals – including the great majority of “marine-certified” electrical service professionals, do not really “get into this stuff.” When faced with an issue, most “professionals” call in “experts” to handle remediation. This is why there can be, and is, a lot of misunderstanding and confusion around this subject.
There are very subtle factors that affect the rate at which anode wasting occurs. These factors vary greatly from place to place. Boaters will fit into all of the affected subcategories, so there is simply no “one size fits all” formula. Examples:
- Galvanic currents increase with water circulation over the hull. The protection requirement can be several times that required in still water. Zincs do not have the capability to automatically respond to changing needs as water velocity increases, as active protection devices (“impressed current devices”) do. So a boat in the Beaufort River in Beaufort, SC, or the Ashley or Cooper Rivers in Charleston, SC, may need more protection than the same boat would need in Marblehead, MA, or Miami, FL, or Marsh Harbour, BS.
- The ratio of cathode/anode surface area. The larger the relative anode area, the lower the galvanic current density on the anode, the lesser the attack. The amount of galvanic corrosion may be considered as proportional to the Cathode/Anode area ratio.
- Boat use. More frequently operated boats (cruisers) require more cathodic protection than vessels infrequently used (floating condos, dock mavens). Relates to item 7, following.
- The conductivity of the water. As conductivity increases, the rate of galvanic activity increases. Related to item 4, following.
- Water salinity. Proportionally more protection is required on a given boat in salt water than in fresh water.
- pH of the water. As pH decreases (acid rain fresh water lakes), the cathodic corrosion rate increases.
- Condition of bottom paint. Deteriorating bottom paint increases exposed cathodic surface area, which increases anodic protection requirements.
Furthermore, when connected to shore power, your boat is part of a electrical network of boats that are electrically interconnected by the shore power safety ground system. The underwater metals on those boats can dramatically alter the cathodic potential (the amount of protection) of your boat. This is particularly true if your neighbor has aluminum (outdrives, trim tabs) and you do not.
A very common rapid zinc wasting condition occurs if you have a neighboring boat that is poorly maintained. If you have good, well maintained zincs on your boat, but your dock neighbor does not, you will be glad to know that the noble metals of the neighboring boat are protected. Your neighbor’s boat is being protected by your zincs, through your generosity, via the shore power network of shared safety ground connections. Since your zincs are the sacrificial metals in this system, they are likely to deteriorate at a faster-than-normal rate. You may or may not consider this generosity to be a good thing. This is a particularly common situation at marinas where a high number of absentee owners reside.
Occasionally we hear that we need to be careful not to “over-zinc” a boat. It is possible to “over-zinc,” but the term is frequently misused in context. In the context of that statement, “zinc” does not refer to the metallic substance; it uses the term “zinc” as a synonym for “anode;” i.e., a mechanical object. So more properly, one should say, “it’s possible to ‘over-anode’ a boat.”
Anodes used on boats are made of Magnesium, Aluminum and Zinc metals. Magnesium is best for boats kept long term in fresh water. Zinc is best for boats kept long term in brackish and salt water. Aluminum is often regarded as acceptable for use in all types of water. Using the wrong anode material in the wrong environment can reverse the galvanic potential between some dissimilar metals or non-metallic, electrically conductive materials under some conditions. Magnesium anodes should not be used long term in salt water. Aluminum anodes can cause harmful over-protection which may result in cathodic corrosion of aluminum parts (outdrive, trim tabs) and possible hydrogen blistering of paint, also known as cathodic disbondment. Some oxides of a few metals, including aluminum, tin, lead, and zinc, are “amphoteric,” meaning they are capable of reacting chemically in both acid (low pH) and basic (high pH) environments. These metals are more susceptible to corrosion in alkaline high pH electrolytes (fresh water) than other metals.
Conclusions: my PERSONAL OPINIONS:
- In general, most boats are better off having Bonding systems than not having bonding systems. if an owner chooses not to have a bonding system, that should be a deliberate, intentional decision made with great forethought. It should be backed up by thorough, professional cathodic measurement testing and with due consideration to lightening as a related technical matter.
- In general, absent an Isolation Transformer, all owners of boats that are fit with shore power service should install a Galvanic Isolator. Galvanic Isolators block the flow of galvanic currents. They greatly extend the life of the boat’s anodes, but more importantly, extend the protection of the most noble (and expensive) underwater metals on the boat.
- In general, the best protection an owner can afford their boat investment is to diligently maintain their anodes (“zincs”).
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Chances are your boat has a ground fault and don't know it... read on...
http://gilwellbear.wordpress.com/category/boat-technical-topics/electrical-topics/boat-ac-topics/ground-fault-example/
An Example of a Ground Fault Incident
Chances are your boat has a ground fault and don't know it... read on...
http://gilwellbear.wordpress.com/category/boat-technical-topics/electrical-topics/boat-ac-topics/ground-fault-example/
An Example of a Ground Fault Incident
When an electric current – either AC or DC – flows in a conductor, that flow of current (electrons) results in the formation of a magnetic field around the conductor. The strength of the magnetic field is proportional to the amount of electricity flowing in the conductor. That magnetic field is what makes motors turn. The magnetic field in the conductor can be detected by placing what amounts to a transformer around the conductor. The transformer is in the form of an iron core “donut” with a sensing winding that feeds a voltmeter. This device is known as a “current transformer.” The current transformer is the same device that underlies the operation of Ground Fault Circuit Interrupters (GFCI), Equipment Leakage Circuit Interrupters (ELCI), ”donuts” in shore power pedestals that measure electrical usage on attached boats, and many, many other forms of electric volt and ammeters.
I have a Sears Model 82369 hand-held clamp-on meter. I like that particular meter because it has the capability to measure both AC and DC amps. The typical Lowes/Home Depot/ACE Hardware clamp-on meter versions are intended for residential use, and usually do not have the capability to measure DC amps. The Sears unit costs about $70, and competes with professional meters costing 3 – 5 times that amount. Even if you never used it to track down AC leakage currents, I find it extremely useful as a DC circuit diagnostic tool aboard the boat.
Clamp-on meters are most usually used on both AC and DC systems to clamp around asingle conductor to measure the magnetic field around the conductor, and thus the current flowing in that one conductor. But when clamped over all of the wires in any one triplex or multiplex AC cable (Romex utility outlet feed, extension cord, shore power cord, etc), the magnetic field generated by the current returning to the source (white wire) cancels out the magnetic field of the current flowing out to the load (black wire). Thus, with everything working normally/correctly, there will be no magnetic field, and the meter will read “zero” amps. Any non-zero meter reading indicates an unbalanced magnetic field, and therefore, the presence of some amount of “leakage” current; i.e., current going out in the hot wire that is not coming back to the source via the path that it should take. On a boat, any current reading in AC shore power cords means that AC current is going into the water.
A summer, 2012, ABYC awareness webinar, hosted by Mr. Kevin Ritz, quoted a technician as saying that, in his experience, as many as 10% of boats in a marina would have problems resulting in AC power leaking into the water. To test and verify that statement, I took my Sears meter and surveyed the docks at my home yacht club. After I zero’d my meter, I found most boats measured at less than about 0.06 – 0.08 amps, so 60 – 80 milliamps. I can’t comment on the accuracy of my inexpensive Sears meter at those low current levels, but since I saw a large sample size of different boats that fit into that range or lower, I concluded it’s OK. I will investigate that assumption further. Of about 80+ boats on our docks, I found four that had leakage currents of 0.25 amps AC or more. I found one with a leakage current of 2.5 amps, and the owner of that boat also told me his diver had reported that he’d “gotten a tingle” while cleaning the bottom and changing zincs. The diver was not hurt, thank heavens! Our yacht club is located in a basin of brackish water on the Chesapeake Bay. But in fresh water, that could easily have been a lethal situation.
This particular boat is a 1970s vintage that has had a lot of modernizing work done to it over time. As would be expected, the work was performed by many different technicians. The modernization upgrades included adding a net new heat pump and a net-new AC shore power inlet circuit to power it. When clamped-on the boat’s shore power, we saw that when the heat pump came on, the leakage current was 2.5 amps, but when the heat pump cycled off, the leakage current went to “zero.” So, armed with my clamp-on meter, I clamped-on the cable supplying the boat’s cooling water circulator pump, but found no leakage. Then I checked the entire heat pump at the power feed to the unit: again, no leakage. That told me the leakage was occurring at an earlier point in the circuit, and not within the heat pump equipment itself. Next, we checked back at the boat’s inlet disconnect breaker, located immediately aboard the boat: At that point in the circuit, we measured 2.5 amps of leakage current. Finally, we checked at the branch circuit disconnect breaker on the heat pump AC panel; i.e., at the breaker that feeds power to the heat pump.
And there we saw the fault that was energizing the boat’s AC safety ground buss. The hot line to the heat pump is served by a 20A circuit breaker, and the neutral and the safety ground are on physically adjacent, but separate, buss bars on the back of the panel, just as they are supposed to be. The original crimp of the terminal on the neutral wire was not made-up tight enough, and over time, the neutral wire had vibrated out of the crimp terminal. Normally, that would just cause power to the heat pump to be lost, and the symptom would have been that it didn’t run. But as amazing as these things can be, by coincidence, the loose neutral had come to rest lying on the adjacent safety ground buss bar. Thus, the heat pump and circulator pump ran normally. Therefore, until the diver reported “getting a tingle” while working in the water under the boat, no one aboard was aware there was any sort of problem. No circuit breaker blew. There was no noticeable loss of cooling/heating performance. Simply, no symptoms.; except that the diver got zapped. This ground fault is one of the three concurrent conditions required to cause power to leak into the water.
I repaired the bad crimp. That corrected the fault that had energized the safety ground buss, and stopped the leakage of AC power into the water. However, somewhere on that boat, there is also a high resistance that is compromising the functional integrity of the the safety ground connection to shore. At this writing, that is still under investigation. It must also be corrected.
My inexpensive Sears clamp-on ammeter is not a laboratory precision tool, but it proved to be an effective screening tool that can be used by lay boat owners and maintenance personnel to identify potentially serious situations. The take-away message is, my Sears hand-held clamp-on meter definitely identified, and confirmed, that there was an AC leakage current problem aboard that boat.
If this boat had been fit with an ELCI (Equipment Leakage Circuit Interrupter), or if the dock had been fit with a 2011 NEC Article 555 compliant GFCI disconnect device protecting it, this problem could not have existed past it’s inception, and an obvious potential shock safety problem would have been foreclosed, with appropriate warning to the boat owner and the marina.
In the above scenario, it was the heat pump circuit that caused the fault that placed AC power on the boat’s safety ground buss. It is important to realize that any electrical attachment or electrical circuit on the boat could fail in a similar manner. Therefore, to do a truly effective screening of your own vessel, it is necessary to not only start and run the heat pump, but every and all AC appliances and equipment, including battery charger(s), water heater, galley and house utility circuits, refrigerator, ice maker, water maker, davit lifts, etc., etc. ALL APPLIACES AND ATTACHMENTS!
Our yacht club plans to have the maintenance crew carry a clamp-on meter with them when they do monthly electric meter readings. They will check every boat connection. We realize this will be a spot check only; i.e., a non-invasive measurement of conditions as of the moment of the check. This does not ensure that every possible failure condition will be identified. Over the course of time, however, the hope – and probability – is that any problems will be identified and repaired on a timely basis. Yes, this procedure works on 120VAC and 240VAC shore power cord cables. We will do this spot check until our shore side infrastructure is eventually upgraded to 2011 NEC Article 555. And for those who doubt the value of the work they do, it seems to me, at least, that what the ABYC is advocating with regard to ELCI devices is “right on the money!”
One last note: marine electrical “experts” do not regard the above screening procedure as “fully” effective. One concern is that the clamp-on meter is placed over all three (or all four) wires in the shore power cord assembly. Used that way, it does not isolate fault currents that might be incorrectly flowing in the safety ground conductor. A second concern is the possibility that a fault may be overlooked. It is possible that a faulty circuit could be inactive at the time of testing. A third is the the concern for lack of sensitivity and/or precision of inexpensive clamp-on ammeters. I agree these concerns are valid. Measurement of only the current carrying conductors (and not also the safety ground) could easily be overcome with the use of a test adapter. Use of such an adapter would necessarily involve unplugging the boat’s shore power cord, and in the absence of the boat’s owner, would be undesirable for a number of reasons.
While I completely agree that this sampling procedure is not diagnostic, it has the advantage of low cost and minimal or no prior electrical skills. Even with its obvious limitations, the disciplined use of a clamp-on ammeter as a simple screening procedure can identify the escape of electricity into the water. I commend it for use by all boaters at all skill levels. If all you do is observe a suspicious condition that warrants calling in a marine-certified professional electrician, you may have saved a life. That life could well be one of your own children or grandchildren, a dear family friend or a beloved pet. So, although not perfect, and not as good as an ELCI device, pretty darned good, all the same!
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http://gilwellbear.wordpress.com/2013/01/12/electric-shock-drowning/
Electric Shock Drowning and Electrical Safety Codes
http://gilwellbear.wordpress.com/2013/01/12/electric-shock-drowning/
Electric Shock Drowning and Electrical Safety Codes
Water, like all electrical conductors, possesses the electrical property of resistance. Fresh water has a relatively high electrical resistance. Salt water has a very low electrical resistance. The open ocean is about 3.5% salt; i.e., for every 1,000 pounds of water, 35 pounds are dissolved salt, or 35 parts per thousand. “Brackish” water is a mixture of salt and fresh water in which the salt content varies from place to place, based on the relative amounts of salt and fresh water present. Brackish conditions exist in marine estuaries, where fresh water rivers flow into salt water tidal basins. Many US coastal waters are brackish. Classics among these are the lower Hudson River and New York Harbor, the Chesapeake and Delaware Bays, the Albemarle Sound and the Tar/Pamlico and Neuse River systems that feed the Pamlico Sound. All of the great sounds of the Carolinas and Georgia are brackish. Ft. Myers Beach, Pine Island Sound, Charlotte Harbor and Tampa Bay in Florida are all brackish in varying degrees. The salt content of these estuarine waters is less than that of ocean water, but more than that of fresh river water. The farther upstream one measures salt content, the less salt is found. Therefore, the electrical resistance of brackish water ranges from high-to-low, where the highest resistance occurs upstream, inland, and approaches that of fresh water and the lowest resistance occurs nearest the ocean, and approaches that of sea water. By contrast to the above, the Great Lakes and Inland River systems (Mississippi, Missouri, Ohio, Cumberland, Tennessee, etc) of the interior US are fresh water systems.
Human blood and body fluids contain about 0.9% sodium chloride, or about 9 parts per thousand. Therefore, the electrical resistance of the human body is in between the electrical resistance of salt and fresh water. The human body is not as good a conductor of electricity as salt water, but it is a much better conductor of electricity than fresh water.
Electric Shock drownings happen to people or animals that find themselves immersed in an electric field that has been established in the water. There are electric “fish barriers” in some places, like the Illinois River at Chicago, the principal reason for which is to contain the movement of invasive species of fish. These barriers intentionally introduce electric currents into the water. But usually, electricity leaking into the water is an unintended situation caused by a wide variety of faults in shore-side electrical infrastructure.
Electric “shock” occurs when an electric current flows through the body. Low to moderate electric currents can cause muscle paralysis. Muscles will contract at as little as 15 milli-amps (mA) of current, making swimming impossible. Once paralysis occurs, drowning can result. If the electric current is high enough, death from electrocution results. The current required to cause cardiac failure is amazingly low; only 60 – 80 mA. Because in general, electricity will tend to follow the path of lowest electrical resistance, the potential for tragedy is greatly increased in fresh water environments. The risk to a person immersed in an electric field in fresh water is high because the electric current will find its “path of least resistance” by flowing through the body rather than through the water surrounding the body. The risk of serious electric shock is relatively less in brackish water and relatively less again in salt water because the “path of least resistance” is through the surrounding water rather than through the body. However, the risk of shock – and electrocution – is never zero!
Boats attached to shore power are a major source of unintentional leakage of electrical energy into the water. The details of this topic are enormously complex, involving current dispersal patterns, voltages gradients in the water, tidal ebb and flood movement, dissolved mineral ion concentrations, water temperatures and a plethora of other factors, but all of the theoretical factors taken together are mainly of interest only to researchers. For boat owners and marina operators, points of actual, practical interest boil down to eliminating the conditions that cause electricity to enter the water in the first place. The assumption has to be that there is no “safe” level of electrical leakage into the water. Fortunately there are just three conditions that we really need to understand. All three are necessary, and all three must all be present concurrently – at the same time – in order for electricity to leak/flow into the water.
The three concurrent conditions that result in AC power leaking into the water are:
1. the origination point – the “derived source” – of AC electricity on the boat must be on-shore; i.e., fed from the shore-based electrical infrastructure (as opposed to an on-board generator, inverter (solar system) or isolation transformer; and
2. a ground fault condition on the boat must result in an unintended voltage being placed on the safety ground aboard the boat; and,
3. the electrical integrity of the safety ground must itself be compromised by an electrical fault condition (internal high resistance due to corroded, loose or broken connection(s), worn/frayed insulation, wiring error or omission, electrical failure within a protected device) which impairs its ability to, or altogether prevents it from, carrying a fault current safely back to the shore-side earth ground.
If all three of these conditions exist concurrently, electric current supplied to the boat will flow through the ground bonding system of the boat, to and through the major zincs and underwater metal components connected to the boat’s bonding system, into the water and back through the water to the shore side earth ground.
1. the origination point – the “derived source” – of AC electricity on the boat must be on-shore; i.e., fed from the shore-based electrical infrastructure (as opposed to an on-board generator, inverter (solar system) or isolation transformer; and
2. a ground fault condition on the boat must result in an unintended voltage being placed on the safety ground aboard the boat; and,
3. the electrical integrity of the safety ground must itself be compromised by an electrical fault condition (internal high resistance due to corroded, loose or broken connection(s), worn/frayed insulation, wiring error or omission, electrical failure within a protected device) which impairs its ability to, or altogether prevents it from, carrying a fault current safely back to the shore-side earth ground.
If all three of these conditions exist concurrently, electric current supplied to the boat will flow through the ground bonding system of the boat, to and through the major zincs and underwater metal components connected to the boat’s bonding system, into the water and back through the water to the shore side earth ground.
Anyone who dives on a boat – professionally or personally – must be aware of the possibility of this set of circumstances. Marinas, yacht clubs and condominium docks must have policies forbidding swimming in their boat basins. Homeowners with “backyard” boat docks must be aware of this phenomena. Homeowners with waterfront properties are at-risk even if they, themselves, do not have boats. These conditions on neighboring boats are equally a threat to the safety of swimmers. Not going into the water is the major preventive measure in electric shock drowning!
In the United States, the National Fire Protection Association (NFPA) develops, publishes and maintains the National Electric Code (NEC). The Canadian Standards Association (CSA) maintains the Canadian Electric Code. The two country’s codes are not always identical, but they are generally compatible. In the US, a major code revision of the NEC was published in 2011. Individual state legislatures adopt the code in order for it to have the force-of-law within the state’s boundaries. Only 21 states have adopted the 2011 NEC as of this writing (4Q2012). Thus, there is state-by-state variation in compliance standards. Individuals must always check with local code authorities for local requirements. This is particularly true for persons holding properties in multiple states. Sections of the NEC code that might be of specific interest to boaters include:
553 – Floating Buildings, and
555 – Marinas and Boatyards. The scope statement for Section 555 covers: “fixed or floating piers, wharves, docks and other areas in marinas, boatyards, boat basins, boathouses, yacht clubs, boat condominiums, docking facilities associated with residential condominiums, and any multiple docking facility, or similar occupancies, and facilities that are used, or intended for use, for the purpose of repair, berthing, launching, storage, or fueling of small craft and the moorage of floating buildings.”
Sections of the NFPA Code that might be of interest to boaters include:
303 – Fire Protection Standard for Marinas and Boatyards. Code enforcement for marinas and boat yards is often handled by municipal code enforcement personnel who are employed by local or state governments. In some jurisdictions, code enforcement is handled by private, independent contractors, certified by the Board of Fire Underwriters, and working on behalf of insurance underwrites who provide fire and liability insurance to the marina facility owner/operator.
553 – Floating Buildings, and
555 – Marinas and Boatyards. The scope statement for Section 555 covers: “fixed or floating piers, wharves, docks and other areas in marinas, boatyards, boat basins, boathouses, yacht clubs, boat condominiums, docking facilities associated with residential condominiums, and any multiple docking facility, or similar occupancies, and facilities that are used, or intended for use, for the purpose of repair, berthing, launching, storage, or fueling of small craft and the moorage of floating buildings.”
Sections of the NFPA Code that might be of interest to boaters include:
303 – Fire Protection Standard for Marinas and Boatyards. Code enforcement for marinas and boat yards is often handled by municipal code enforcement personnel who are employed by local or state governments. In some jurisdictions, code enforcement is handled by private, independent contractors, certified by the Board of Fire Underwriters, and working on behalf of insurance underwrites who provide fire and liability insurance to the marina facility owner/operator.
These shore-side marina codes will directly affect boaters more-and-more as time goes on. Boats with on-board, non-compliant wiring problems will increasingly often be “caught” and “identified” at marina visits. This will certainly result in the inconvenience of not having shore power for the boat at that marina. Depending on the attitude of the particular marina where this happens, you could be asked to depart. If you have a properly installed and working Equipment Leakage Circuit Interrupter (ELCI) device installed, and the ELCI device does not report problems aboard, the shore power infrastructure will also be happy. (More on ELCIs below.)
The American Boat and Yacht Council (ABYC) adopted an updated E-11 Electrical Standard in July, 2012. This standard is fully compatible with it’s NEC and NFPA counterparts, butapplies specifically to AC and DC electrical installations aboard boats. It applies to all pleasure craft registered or documented in the United States. Enforcement of ABYC E-11 is not handled through municipal code enforcement authorities, but rather through certified yacht surveyors (AMS, SAMS), and the influence survey reports carry with the insurance underwriters who write liability and hull insurance on pleasure craft. This is most analogous to residential code compliance inspections done by independent fire inspectors.
The 2012 ABYC E-11 electrical standard includes a requirement for manufactures to install a device called an Equipment Leakage Circuit Interrupter (ELCI) on all new boats built after December 31, 2012. This device is technologically very similar to GFCI devices installed in residential AC systems and on boats. GFCI devices are intended to protect people directly. ELCI devices protect people indirectly, by monitoring and automatically disconnecting faulty equipment. The theory here is very simple! All of the AC electric current flowing onto the boat in the hot supply wires (“black” for 120VAC shore power, or “black” and “red” for 240VAC shore power) should flow back off the boat, returning into the shore power supply. The returning current flow can be in the neutral (“white”) wire and/or any of the “current carrying conductors” feeding a 240V circuit, and will be in the neutral (“white”) return conductor for 120V circuits. The ELCI senses the hot and neutral lines using a Current Transformer. It detects any difference in current flowing onto and back off the boat within those “current carrying conductors.” Any difference in flow, however large or small, represents current flowing into the water. ELCI devices are designed to be less sensitive than the GFCI devices to minimize “nuisance trip” or “false trip” problems leading to customer dissatisfaction. The 2012 disconnect criteria for ELCI devices is: an AC current of 30 milliamps (mA) or more that lasts for a duration of at least 100 milli-seconds (mS). If the trip criteria is reached, the ELCI device will shut off all shore power feeding the boat. Such a condition is, after all, a potentially lethal safety issue, so correction of the fault condition(s) causing the device to trip will be necessary to get power restored on the vessel.
Reference:
A two-part series of webinars on Electric Shock Drownings was sponsored by the ABYC in the Summer of 2012. Part 1 deals with the phenomena, itself, and the related boat-side issues. Part 2 deals with the shore-side infrastructure. Part 1 is easier to understand. Part 2 is technical and oriented to code compliance for marina owner/operators. The two videos were bootlegged, and are available on http://www.youtube.com. They are best watched in order.
Part 1 is here: http://www.youtube.com/watch?v=O7-s_mdEPb0&feature=youtu.be;
Part 2 is here: http://www.youtube.com/watch?feature=player_detailpage&v=nlBIbgBtCoE.
Part 2 is here: http://www.youtube.com/watch?feature=player_detailpage&v=nlBIbgBtCoE.
Note that the second video was recorded live from a computer session. There are two places where the audio is interrupted by phone calls received by the person doing the recording. The charts remain visible, and the interruptions are distracting, but do not seriously diminish understanding.
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http://gilwellbear.wordpress.com/2013/01/12/residential-ac-electricity/
AC Electricity: A Commonly Misunderstood Key Concept
http://gilwellbear.wordpress.com/2013/01/12/residential-ac-electricity/
AC Electricity: A Commonly Misunderstood Key Concept
In North America, 60-cycle, three phase generating stations (abbreviated “3-phase,” often “3-Ø” on circuit diagrams) and a 3-phase power distribution grid are the absolute standard. Three phase power is commonly used in industrial and commercial applications; it’s unusual, but possible, to have three phase power in single family residential dwellings. Three phase power is actually quite common in apartment, condo and town house multi-family dwelling buildings, which are seen by the electric power grid as commercial buildings. Three phase power is also quite common in marinas and boatyard facilities. This is the subject of another post on this site. Regardless of how power is supplied to the building, single phase circuits power the overwhelming majority of residential applications.
Typical single phase transformer in residential/light commercial applications
Single phase residential AC electricity comes into a building from a transformer. The primary winding (input) of the transformer connects to one leg of a 3-phase primary distribution line, usually located on a pole (or underground) at the street. The secondary winding (output) of the transformer connects to the building. The “secondary” is a single coil with an electrical connection at it’s physical and electrical mid-point; it’s physical and electrical “center.” In North America, that “center tap” is referred to as the “neutral” and the two respective ends of the winding are each referred to as “hot” lines. The neutral is tied to earth ground in the building, and that provides a fixed, known electrical reference point for the system in the building. In written articles and on electrical diagrams, the neutral is abbreviated “N,” and the hot lines are abbreviated “L1″ and “L2.” This connection topology, or configuration, is a “single-phase, 3-wire, mid-point neutral” system. The voltage between L1 and L2 is nominally 240VAC. The voltage between the neutral, N, and either one of the hot lines, L1 or L2, is nominally 120 VAC.
This above configuration is often often incorrectly referred to as having “two phases.” You do *not* get two-phase output from single phase input. The concept here is widely misunderstood, even by some electricians. The cause of the confusion is the manner in which measurements are commonly made. In a grounded neutral system, the measurements are virtually always taken using the grounded neutral as the measurement reference. Performed in that manner, the measurement reference point would be the center tap, or in the middle of the transformer’s secondary winding; i.e., not at one of the winding’s origin or terminus points, L1 or L2. So, the result is, one half of the winding will appear backwards when compared to the other half.
If an oscilloscope is connected to initially measure the voltage waveform with its negative probe at L1 and its positive probe at the center tap (CT), and then a second measurement is taken by moving both probes so the negative probe is relocated to the CT and the positive probe relocated to L2, the two voltage waveforms would appear correctly, in-phase with each other. If, on the other hand, an oscilloscope negative probe is connected at the CT, and measurements are then taken by moving only the positive probe, first to L1 and then to L2, the respective voltage waveforms would appear 180° out-of-phase WITH RESPECT TO THE CENTER TAP; i.e., one of the waveforms would appear “backwards” in comparison to the other. This false indication reflects the error in measurement methodology, and creates the appearance of the waveforms being out-of-phase. This is a measurement anomaly only. Again, you do *not* get two-phase output from single phase input.
Voltage waveforms in a single phase transformer in residential/light commercial applications
The lay public and some residential electricians routinely refer to the two halves of a 240V circuit as “Phases.” It’s a “terminology shortcut” like so many we use in everyday conversation. In actual practice, there’s nothing wrong with that as long as the underlying concepts are clearly understood. I personally prefer to call the two circuit halves “legs;” i.e., leg 1 circuits and leg 2 circuits (for L1 and L2). The important concept, though, is that a 240VAC residential circuit is not a two-phased circuit.
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http://gilwellbear.wordpress.com/2013/03/19/elci-a-primer/
http://gilwellbear.wordpress.com/2013/03/19/elci-a-primer/
ELCI – A “Primer”
Normally in a 120V AC circuit, AC current flows from its source to its intended load on an energized, or “hot,” current-carrying conductor and then returns to the source on the neutral current-carrying conductor. In a 240V AC circuit, current can return on the second “hot” current carrying conductor or on the neutral, or both, depending upon the combined nature of the loads attached to that circuit. A safety ground is not necessary to enable these simple AC electric circuits to work, but is required by all fire and electrical codes, and is alwaysadded, as a means to keep living beings safe from shock and electrocution. The neutral conductor is held at ground potential by attachment to the safety ground. This connection – known as the “bonding conductor” – is located at the “derived source” of the AC electric service; i.e., the “main service disconnect panel.” The safety ground conductor is intended to protect against faults; it is not intended to carry any of the current returning to its source from a properly connected and properly functioning load.
A “ground fault” is an unintentional connection between the “hot” current-carrying conductor and any possible conductive return path that leads back to the source of ACother than the normal neutral return path. On a boat, “fault” circumstances (described in the article on Electric Shock Drownings posted on this blog) can cause AC return currents to flow through the water to a shore-based infrastructure. This can be lethal to people, pets and wildlife in the water.
A Residual Current Device (RCD) is a type of device that disconnects the load from its source of power when a “fault” current is detected. RCD devices generally provide two protective electrical functions: first, they provide the over-current disconnect function with which we are all familiar in conventional fuses and circuit breakers; second, they detect leakage currents and disconnect the load from the source if leakage currents rise above a pre-set magnitude. There are also leakage current detection devices that do not include over-current protection. As the term “Equipment Leakage Circuit Interrupter” (“ELCI”) has emerged in the US marine marketplace, it is common among boaters and many marine industry sources to refer to both kinds of devices by the common term, “ELCI.” They in fact have different applications.
One form of RCD with which all of us are already familiar is the ubiquitous household Ground Fault Circuit Interrupter (GFCI) used on the utility outlets installed in our homes and work places. GFCI devices are designed to protect people from shock hazards, and specifically, the most vulnerable and sensitive people in society: small children and the elderly. To protect even the most sensitive among us, GFCIs have a very sensitive disconnect trip point: 5 milli-amps (mA) lasting for a short duration of 7 milli-seconds (mS). Since all electrical devices will naturally experience some very low levels of leakage, and surges do occur on the electrical supply, and the total leakage currents in a circuit are cumulative, this low trip level will only protect a small number of attached devices without becoming subject to “nuisance trips.” ELCI devices meant for use on boats are spec’d to be significantly less sensitive than GFCI devices. Remember, they are not there for the same purpose. GFCI protects people, ELCI protects equipment. Marine ELCI devices are spec’d to allow leakage currents of up to 30 mA that last for as long as 100 mS. Again, ELCI is a technology intended to protect equipment; it protects people only indirectly. These disconnect set-point values are established as a compromise between the levels of AC current that may be hazardous to humans and animals, and the avoidance of “nuisance” trips that discourage adoption and use of the technology.
I personally believe the simple act of installing ELCI on a boat will result in exposing many non-symptomatic legacy electrical wiring problems that currently exist in hiding, lurking, waiting silently to become apparent and dangerous. I think there are a lot of them. Boat owners should all expect to find some, and consider themselves lucky – or extraordinarily well prepared – if they do not. This is especially true for older boats. These issues live and hide in both the on-board AC electrical system and in the boat’s DC system and DC bonding network, the latter being a subject we almost never talk about, and is largely considered to be in the category of a “black art!”
For example, here’s a simple and common non-compliance occurrence for those without isolation transformers. The ABYC E-11 electrical standard requires that the shore power neutral and safety ground must NOT be connected together aboard a boat that is directly attached to a shore power AC “derived source.” This is exactly the same as the NEC’s residential code requirement for a sub-panel that is subordinate to a main electrical service panel. However, for a boat fit with an on-board generator or an inverter, the neutral and safety ground must be connected together at the frame of the device when they are operating as AC power sources. In every case, the rule is that the neutral and safety ground are to be “bonded” – connected together – at their respective “derived source” and only at their “derived source.” Aboard a boat, the above code requirements mean that both the hot line(s) and the neutral must be switched “out” when the boat is connected to a shore power “derived source” and switched “in” when the “derived source” is the onboard genset or inverter. I know of many boats that only switch the hot conductor, so there’s a clear code and safety violation right there. (Refer to footnote 1, below in this article, for configurations involving isolation transformers.)
Another common non-compliance example occurs frequently on older boats. Many older boats will have neutrals and safety grounds, mixed together, wired to the same common buss bar. Many boats will have these problems – and others like them – from years of work having been done by unqualified people, modestly familiar with residential work, able to “get it to work,” but not qualified to correctly perform marine installations. Or perhaps, from attempts to save money by using residential electrical equipment or materials bought at big box home centers or hardware stores that is not intended for use in marine applications.
If the neutral and the safety ground are interconnected on the boat in a directly connected shore power configuration, a parallel return path is created in the safety ground return line with the infrastructure bond located at its correct place – at the “derived source” – in the shore-side infrastructure. In that case, some amount of current WILL return to the source, not in the neutral where it’s supposed to be, but on that parallel safety ground path (and, also through the water). That’s both a code violation and a fire and safety concern. ELCI will detect that fault condition and trip the boat offline.
Yes, these examples will be – as part of installation troubleshooting – an inconvenience. The boat won’t get power back again until all of the previously hidden issues are located and corrected. But in the long run, that inconvenience truly is “good for everyone.”
The reason it’s “good for you,” however painful you perceive the inconvenience of locating and correcting these hitherto non-symptomatic faults to be, is this: NEC Article 555 and NFPA Section 303 are driving marina and boatyard owners/operators to install ground fault detection circuit disconnect breakers (analogous to ELCI, except in the shore power infrastructure) on their 30A and 50A shore power services. That equipment has a higher yet trip set-point (100 mA, 100 mS) than ELCI.
Imagine this scenario. You arrive just at dark at a marina fit with shore power ground fault sensing equipment. You have a hidden, previously unknown and non-symptomatic wiring fault aboard your boat. When you connect to the marina shore power pedestal, expecting to shortly be enjoying dinner and an adult beverage, the marina infrastructure safety equipment disconnects the AC power to your boat. AND DEPENDING ON HOW THE MARINA DOCKS ARE WIRED, MAYBE TO OTHER BOATS AS WELL. That would not make your new dock neighbors happy! At a minimum, this scenario would result in you not having shore power at your boat for the duration of your visit. But worse, if you blow the dock service, you may well be asked to leave the marina. Yikes. Leave? Don’t we all know of marinas that’d be glad to throw us out to reduce their liability risk and the great dissatisfaction this scenario would bring to other customers?
Residual current devices are, first, a technology that saves lives. They are not new, and are extensively used in industry and residential applications in many parts of the world. I RECOMMEND THE INSTALLATION OF ELCI, FOR EVERY ELIGIBLE BOAT, AS SOON AS POSSIBLE. Marine ELCI device trip specs should accommodate all the cumulative permissible electrical leakage present in on-board electrical equipment. Getting an ELCI installed properly and working properly will expose any asymptomatic legacy problems aboard your boat. Correcting those issues will not only make your boat safer, it will foreclose cruising issues like that described above.
Blue Sea Systems PN 3117, enclosure contains 2, 30A ELCIs.
Looking at what’s available for the boater in the pleasure craft market today (1Q2013), Blue Sea Systems is the only marine manufacturer currently offering true RCD solutions for pleasure craft owner/operators. They offer single 120V (30A) and 240V (50A) units, and they offer a unit that accommodates 2, 120V (30A) circuits on the same boat in a single physical surface-mount enclosure. These units provide both over-current disconnect protection and ground fault leakage detection. They do require some available physical space for the installation. Because they provide over-current protection, they can replace existing over-current main disconnect breakers.
North Shore Safety PGFM Control Module
The Hubbell solution (non-solution, really) is more complicated. Hubbell does not make or brand an ELCI device. They manufacture plastic and SS shore power inlet housings with which all pleasure craft boaters are probably familiar. North Shore Safety Systems makes a Control Module unit that fits into the Hubbell inlet housing. It consists of a current transformer and the “test” and “reset” buttons that operate the ELCI breaker. Airpax-Sensata Technologies makes the disconnect RCD breaker that is controlled by the North Shore control module current transformer (leakage current sensor). Here’s a <SNIP> from the Airpax-Sansata brochure:
“The LineGard™ PGFM product family provides ELCI (equipment leakage) ground fault sensing and is designed and manufactured by North Shore Safety, a leader in innovative safety products. The PGFM series operates in tandem with a Airpax ™ LEL series, UL 489 listed circuit breaker, with shunt trip and auxiliary switch manufactured by Sensata Technologies. The combined assembly of the PGFM and LEL series meets the requirements of ABYC E-11 for ground fault protection and main shore power circuit protection. The PGFM constantly monitors the current balance of the conductors (wires / cables) supplying power to the load. When a ground fault of 27mA nominal (30 mA max) occurs, the PGFM uses the LEL’s shunt trip coil to signal the breaker to trip.”
North Shore Safety and Sensata Technologies have formed a joint-venture company, Techsol, through which they plan to market this complete ELCI solution via a distributor/dealer network. Techsol is not yet “up-and-running” in this venture. So today, it would be difficult-to-impossible for a pleasure craft owner/operator to obtain the components of this solution. However, this arrangement does appear to have space advantages over the RCD version from Blue Sea Systems, because the physical breaker and its enclosure can presumable be located remotely from the current transformer, in an available physical location in the electrical closet of the boat, where physical space may be more available. A boat with 2, 30A shore power inlets would need two pairs of these components, each to serve one of the two shore power inlets.
Finally, it appears that some offshore (Canada, EU, Australia, South Africa, New Zealand) RCD devices may also meet the UL certifications required by ABYC E-11 for ELCI. One such product is a 40A, 120/240V, 50/60 Hz unit made by the French company, Legrand. Looking around the Internet, I also found other EU manufacturers in the RCD market. The web sites I found are generally technical, and often not suitable for boat owners without an electrical background. In any case, I think it’s fair so conclude that the US marine market is not yet ready to serve the US pleasure craft owner/operator in this technology. I am actively researching alternatives, and pursuing further information. Watch this space.
A final note on ELCI. I approached the ABYC electrical committee for clarification of their language on implementation dates for ELCI. The response I received was that the published 12/31/2012 implementation deadline for ELCI applies to new boat manufacturers. Thus, any boat manufactured starting in 2013 must have builder-installed OEM ELCI protection aboard. Boat owners doing “extensive” electrical upgrade/remodeling/retrofit after 12/31/2012 would also be expected to install ELCI as part of that “extensive” rework. Of course, your definition of “extensive” could be different from your insurance carrier’s definition…
For all of the rest of us, retrofit is not yet “required.” However, a compliance date for “retrofitting the fleet” will emerge, and will probably be in the 2014~2016 timeframe. That said, don’t delay! If the Blue Sea Systems technology meets your requirements, proceed with that. ELCI IS AN EXCELLENT TECHNOLOGY, AND I RECOMMEND IT TO ALL BOATERS AS AN ELECTRICAL SAFETY ITEM! ESPECIALLY, I RECOMMEND IT AS SOON AS POSSIBLE FOR THOSE WHO BOAT PRIMARILY IN FRESH WATER, LIKE THE GREAT LAKES AND THE INLAND RIVER SYSTEM.
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Note 1: The nature of isolation transformers changes on-board wiring details. The ABYC E-11 electrical standard requires ELCI be installed on the current carrying conductors of the primary side of the isolation transformer unless the isolation transformer is within 10 feet (3 meters) of the shore power inlet. Furthermore, because the transformer secondary is an on-board AC “derived source,” the secondary neutral of the transformer is permanently attached to the “Main AC Grounding Buss” of the boat, as is the generator neutral. In this specific case, a generator transfer switch need only transfer the hot lines between the on-board loads and the transformer’s secondary or the genset. Refer to ABYC, E-11, 2012, Diagram E-5, page 36, for details. Note also, the referenced E-11 standard contains only one diagram showing a generator in an isolation transformer configuration, and that diagram depicts a 240V on-board configuration. It does, however, illustrate the intent of both on-board ELCI installation and proper neutral-to-safety ground bonding with an isolation transformer.
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