Excessive amperage leak?

[sdowney717]

I just thought of another advantage to a GFCI protected circuit.
If the circuit develops a ground fault, current is flowing out on the ground which can destroy your equipment and wiring.
It is like a short circuit with high resistance.

I had a ground fault on a sealed Carling water tight switch in a plastic outdoor electrical junction box that turns on a raw water wash down pool pump. I suppose that cheap foam gasket on the cover failed. So of course the GFCI immediately sensed the bad current flow cutting the power. I also have a small relay in that box for a remote on switch for the pump controlled at the helm, which had gotten wet and which was the basic ground fault problem.

I am certain if current had just been allowed to flow for months, that relay would have been destroyed, maybe the switch also, maybe some of the wiring in the box, so the GFCI saved me those parts. I have seen the effects of stray current, destroys electrical stuff.

All I had to do was dry it all out. This time I moved the relay off the floor of the box so it can't sit in any water.

Being all plastic so not really a shock hazard, you might never know there was a problem. And not enough current flow to create heat to cause a fire or trip a regular breaker.

 

[sdowney717]

Follow up regarding the boat in question in original post. The owner did some visual investigation and says the neutral wires on both the original electrical panel and the second (added) panel are both interconnected at the single shore-off-generator switch. So he says he's going to add a second rotary switch. (As an aside, I believe there are single (long cylindrical) switches available that would accommodate two separate circuits on one control knob).

In any case I am still not clear about something...and it's relevent to the way we check other boats that use two 30 amp cords. Assuming the interconnected neutrals at the rotary switch...let's say that he only plugged in one 30 amp cord. What would we be reading with the Fluke? And let's say he then plugs in two 30 amp cords (same interconnect at the rotary switch....what would we be reading on each 30 amp cord?

Now the same questions for a boat without the interconnected neutral wires?

I ask these questions because there are many old boats with added panels....and I suspect more than a few with interconnected grounds like this guy.

A final question...are we absolutely "safe" in terms of the stray current question if we put the fluke on the fat cord of a 50 to two 30 Y splitter? Are some splitters "better" than others in this regard?

This obviously goes to issues with a very rudimentary test methodology...but it is what it is and we're trying to be as safe as possible. Further there are a huge number of cruising boats on the Lakes including looper boats that might have been "safe" in salt water...but much less "safe" in the Great Lakes. Modern sensors on the dockside system are just not in the cards in many locations.

If only one shore cord plugged in, and your measuring just one shore cord and that shore cord is sharing a neutral with the other shore cord, the fluke would not detect any problem at all, as all the current is flowing back on the neutral of the one shore cord, the other shared neutral is not flowing any current since it is not plugged in to the dock. It is just disconnected.

In order to check these things, the electric system needs everything hooked up and running. An appliance might not show a ground fault if is off and cold.

Really a twin 30 amp AC system on a boat is like two isolated separate AC systems, no wires should ever interconnect to the other shore cord wiring, except for the green safety ground wire which normally carries no current.

 

[BSGK]

The real danger is fresh water which is not very conductive. Current will preferentially go through your body back to the dock. Saltwater is usually more conductive than a human, so there is less of a risk.

How can it go through your body when there is no circuit there? If you are immersed in water you are at the same potential as the water and unless you complete the circuit there is little risk.

 

[KDMann]

Clamp meter test...

Rufus: If you were clamping the entire shore cord, that is only the preliminary test. To truly determine if a particular boat is leaking current into the water column you have to use a break out adapter that allows the test to be performed by clamping L and N (120V shore power) or L1, N, & L2 (240V shore power)....

I'm here to learn.


That said, my understanding is that clamping the entire cord is definitive as a means to identify any immediate electro-shock drowning risk. A number of marinas I've been in use this method for both transients and new arrivals.


A number of divers I've talked to are now carrying one of these, less that $150 on Amazon...


REED ST-9809 AC Leakage Current Tester


This makes sense to me because (for example), if you clamp the entire cable and read zero milliamps, you know that every milliamp that is going 'out' on L1(L2) is coming 'back ashore' via either N or G. Therefore...you know that there are zero milliamps exiting the boat to ground through the water.

Now...if some of those milliamps are coming back via the grounding conductor instead of on N, that's a potential problem, but does not present a drowning risk. Rather, this indicates faulty on-board equipment with neutral-to-ground leakage. However, since this leakage is coming back through the shore-power green wire (and not through the water), swimmers would be safe.


Do I have this right?


Please correct me if I'm wrong.

 

[diver dave]

An electric field gradient can well exist in water.

Years ago, cave divers were jolted 100 ft deep in very clean spring water, due to a lightning hit on the surface.

 

[gsholz]

Even if freshwater was a pure insulator (it is not), you could still get zapped depending on how you orient your body with respect to the electric field in the water. If you are oriented parallel to the field lines (same potential) nothing will happen, if you swim perpendicular to the field lines, a voltage potential will build up which can stop your heart and/or paralyze your muscles. Same thing happens when lightning strikes on land. You do not want to lay down on the ground. Make yourself as small as possible with both feet close together.

For more information look up Electric Shock Drowning.

 

[diver dave]

Here is one for you. Electrical workers in a switchyard directly under a 345kVolt line that is 30 feet above. He stands on a well grounded platform. The air has over a 10 kV per foot electric field gradient. So, standing upright, one is exposed to around 60kV of field strength. No shock is felt-why?

 

[gsholz]

For you to actually feel a shock some current has to flow. That is the air needs to be ionized. How close can you get to the 345kV line before bad things happen? I'd want to stay a few feet away.

 

[diver dave]

Yes. So a good insulator is the place to be in a high electric field. Or, a good conductor. You dont want to be in a semiconductor.
I’m poking at the first sentence in post 65.

 

[texasnielsen]

For the OP... I am trying to learn and understand leakage myself.... ?

https://www.marinadockage.com/technical-bulletin-understanding-ac-leakage-current/

 

[sdowney717]

For the OP... I am trying to learn and understand leakage myself.... ��

https://www.marinadockage.com/technical-bulletin-understanding-ac-leakage-current/

Yes, using a clamp meter on all 3 wires in the cable will not show up all ground faults. Its why I dont think its a good test.

BUT using a GFCI on the shore cable will detect the ground fault that is dangerous to your life. Its just much better way to test for leaks. Unless you break the ground wire out of the test, the fluke would be worthless.

AND an ELCI breaker will miss a lot of significantly dangerous ground faults as the threshold is much higher at 30 ma vs 6 ma.

In the marina environment, there are two different scenarios of leakage current. One scenario is illustrated in Figure 6. This example shows the 100 mA of leakage current flowing back to the shore power receptacle on the green (i.e. ground) wire within the shore power cord. Therefore, the leakage current is contained within the shore power cord. The ground wire should never carry current in normal operation of the electrical system. As shown in this example, if a clamp-on meter is used to clamp on the entire shore power cord, the meter would display zero current because the magnetic field is balanced. In most cases, this scenario of leakage current is a neutral-to-ground connection inside the vessel.

 

[CharlieJ]

KDMann #64:

That said, my understanding is that clamping the entire cord is definitive as a means to identify any immediate electro-shock drowning risk. A number of marinas I've been in use this method for both transients and new arrivals.

This is not a "definitive" method-it is the first step. Here are a couple of points:
1. This method will identify the gross leakage current at that instant in time. To increase the validity of this test, every single piece of AC electrical equipment aboard the subject vessel must be operating while testing the shore cord.
2. Unfortunately this method will also identify leakage current that is being produced by another vessel on the same electrical circuit that is returning to the source via the subject vessel's connection from safety ground (green wire) to the subject vessel's ground buss and hence to the water column.

This makes sense to me because (for example), if you clamp the entire cable and read zero milliamps, you know that every milliamp that is going 'out' on L1(L2) is coming 'back ashore' via either N or G. Therefore...you know that there are zero milliamps exiting the boat to ground through the water.

True, but I generally find between 2 and 10mAAC on 85% of the shore cords that I clamp using a Yokogawa 30032A clamp meter.

Now...if some of those milliamps are coming back via the grounding conductor instead of on N, that's a potential problem, but does not present a drowning risk. Rather, this indicates faulty on-board equipment with neutral-to-ground leakage. However, since this leakage is coming back through the shore-power green wire (and not through the water), swimmers would be safe.

Unfortunately, any leakage will return by all paths back to the source. Clearly, the majority of the leakage will return via the safety ground wire if, and this is a very big if, the safety ground circuit is actually a redundant, low impedance conductor back to the source. If the shore power safety ground is degraded in any way, more of the leakage current will return via the water path. If the leakage current creates a steep enough voltage gradient in the water, it may become lethal for a swimmer that is crossing the gradient lines perpendicular to those lines.

As a practical matter, even though an annual test of the shore power integrity is required by the NEC, few marinas are performing this test and the safety ground conductor may not be "low impedance" and is therefore ineffectual.

sdowney717 #71:

BUT using a GFCI on the shore cable will detect the ground fault that is dangerous to your life. Its just much better way to test for leaks.

As a practical matter, if the subject boat plugs shore power into a GFCI protected receptacle and has > 6mAAC leakage (most boats do), the GFCI will trip and with no power to the boat troubleshooting for N>G or L>G faults cannot proceed. So, a GFCI will protect, but it is not a testing device.

Its just much better way to test for leaks. Unless you break the ground wire out of the test, the fluke would be worthless.

The Fluke (Yokogawa, Megger, AmpProbe) is not "worthless" when clamping the entire shore power cord. It is a preliminary test. If the reading is close to zero then there is no field being developed in the water at that instant in time. The definitive test is clamping the ungrounded and grounded conductors to emulate the ELCI/GFCI while every piece of AC equipment is operated on the subject vessel.

AND an ELCI breaker will miss a lot of significantly dangerous ground faults as the threshold is much higher at 30 ma vs 6 ma.

The misunderstanding is that a 30mAAC leak will not develop enough of a voltage gradient to harm a human. That is why it was selected. The voltage gradient has to be >2V/ft in order to be lethal. 2VAC/ft equates to about 100mAAC leakage in fresh water and about 500mAAC in sea water. Note that at these levels, the nominal human will feel the electric field.

I am not advocating allowing leakage to these levels. I am simply providing the science behind the prescribed limits.

As always, "The devil is in the details. But so is salvation."

 

[sdowney717]

gfci can be used as a testing device by turning off all your distribution breakers in the panel. Then turning on each, one at a time. If you have a ground faulting circuit, when you turn on that breaker, the gfci will trip off.
If the GFCI trips with all panel breakers off, then you know the problem is between that panel and the gfci.

the E in ELCI means equipment protection. It will allow enough current flow to be dangerous to a person. Othewise whats the point of the GFCI set to 6 ma. All the codes would then allow for ELCi in circuits for personal protection, they set the thresh hold much lower for a good reason.

The difference between ELCI and GFCI is only in the allowable current thresh hold before it trips off the power. They both work the same way.

If most boats exceed the 6ma ground fault currents, then it needs to be fixed. Because its a good idea, means your leaking AC current already and it might just got a lot worse. Do you ever know of electrical things that get better with time? And some dock share a single ELCI breakered circuit, so your lower ground fault defect and another slips ground fault defect leaking current adds up to over 30 ma, which will trip an ELCI too, shutting off power to more than your boat. There are devices having 100 ma thresh holds in use powering a whole dock string of power plugs. No single boat would trip off power, but if everyone's leaking some power, it adds up.

My boat does not exceed the 6 ma threshhold, and it was not hard to do that. I also have some multi decade old appliances. Such as the oven, couple wall heaters, heat pump. If everything is well wired, dry and in good condition, you wont trip a GFCI. If some device is tripping a GFCI, maybe you cant fix it, by design its just crud.

I dont understand why anyone would fight against using them on boats. They do save lives and save equipment, such as slowly corroding away due to a ground FAULTS leaking out currents.

Faults means its FAULTY.
GFCI means Ground fault circuit interrupter.

 

[psneeld]

From a friend in the know......



"I mentioned the Fluke 369 (that I use to test our installations) as opposed to all those mentioned in the thread that are not suitable for detecting and measuring leakage current.

"When testing the grouped live conductors of a circuit, the magnetic fields produced by the load currents cancel each other out. Any imbalance current comes from leakage from the conductors to ground or elsewhere. To measure this current, a leakage clamp meter should be able to read less than 0.1 mA."

https://www.fluke.com/en-us/learn/blog/clamps/leakage-current-measurement-basics. "

 

[CharlieJ]

sdowney 717:

gfci can be used as a testing device by turning off all your distribution breakers in the panel. Then turning on each, one at a time. If you have a ground faulting circuit, when you turn on that breaker, the gfci will trip off.

Unless there is a N>G bond onboard, or an isolation transformer without soft start, or the shore power cord itself is faulty, or the inverter/charger N>G relay faults, etc., etc. Under these very typical conditions, the GFCI/ELCI/RCD will trip as soon as the shore power breaker is closed. It is for this reason that the revision to the NEC currently under review recommends that every marina have one shore power pedestal without an RCD that can be used for troubleshooting.

...and some dock share a single ELCI breakered circuit, so your lower ground fault defect and another slips ground fault defect leaking current adds up to over 30 ma, which will trip an ELCI too.

Thanks for pointing this out. Leakage on a circuit is additive and depending on which schema the marina has used trying to comply with the NEC from 2011 onward (there have been several iterations, not all of them well thought out), there could be a single 30mA/100mS RCD protecting an entire dock of 10 slips. As an example: Nine boats are contributing 2 to 4mA leakage apiece for a total of 27mA and the transient boat comes in with his 4ma of leakage and trips the whole dock. And yet his onboard ELCI (30mA/100mS) does not trip because he is relatively clean. Pitchforks and torches ensue!!

 

[sdowney717]

sdowney 717:

Unless there is a N>G bond onboard, or an isolation transformer without soft start, or the shore power cord itself is faulty, or the inverter/charger N>G relay faults, etc., etc. Under these very typical conditions, the GFCI/ELCI/RCD will trip as soon as the shore power breaker is closed. It is for this reason that the revision to the NEC currently under review recommends that every marina have one shore power pedestal without an RCD that can be used for troubleshooting.


Thanks for pointing this out. Leakage on a circuit is additive and depending on which schema the marina has used trying to comply with the NEC from 2011 onward (there have been several iterations, not all of them well thought out), there could be a single 30mA/100mS RCD protecting an entire dock of 10 slips. As an example: Nine boats are contributing 2 to 4mA leakage apiece for a total of 27mA and the transient boat comes in with his 4ma of leakage and trips the whole dock. And yet his onboard ELCI (30mA/100mS) does not trip because he is relatively clean. Pitchforks and torches ensue!!

The GFCI will trip off first before the ELCI trips off. If you have an isolation transformer, then just check for ground faults after it. If the cord is bad it will also trip without it even plugged into the boat.
I have a GFCI protected extension cord to test the whole boat with. All my GFCI protection begins at the distribution panel on the boat.

Our dock has no ELCI protection yet, and I am in VA, and have not heard about any plans to change it. I have been to 5 marinas in 10 years here and none of the docks had any GFCI or ELCI protection. Makes me think its voluntary.
But the yard power on the hard for when your working on the boat was all GFCI breaker protected, go figure.

 

[CharlieJ]

The GFCI will trip off first before the ELCI trips off.

Of course. RCDs only protect downstream.

If you have an isolation transformer, then just check for ground faults after it.

And how do you do that if you cannot get power aboard?? Hence the allowance by the NEC for a non RCD protected pedestal for troubleshooting.

If the cord is bad it will also trip without it even plugged into the boat.

If a phase to ground hard fault exists. Not so if there is salt water tracking internal to the plug or a break down in conductor insulation.

Makes me think its voluntary.

Absolutely not voluntary. The National Electrical Code recognized electric shock drowning and made started making substantive changes to the applicable sections with the 2011 revision. It is up to each state to adopt the version of the NEC that they desire to be used and it is up to the Authority Having Jurisdiction (AHJ) in each governmental entity (village, town, city, etc.) to apply the NEC for any permitted work performed.

 

[sdowney717]

Of course. RCDs only protect downstream.


And how do you do that if you cannot get power aboard?? Hence the allowance by the NEC for a non RCD protected pedestal for troubleshooting.


If a phase to ground hard fault exists. Not so if there is salt water tracking internal to the plug or a break down in conductor insulation.


Absolutely not voluntary. The National Electrical Code recognized electric shock drowning and made started making substantive changes to the applicable sections with the 2011 revision. It is up to each state to adopt the version of the NEC that they desire to be used and it is up to the Authority Having Jurisdiction (AHJ) in each governmental entity (village, town, city, etc.) to apply the NEC for any permitted work performed.

If you ground fault is small, it wont be tripping an ELCI, so you will have power aboard to test with a gfci.

Sure if a cord has such a short between phase to neutral that is not a ground fault, but likely it will become one, its may get hot and melt the insulation. I had a pinched shore cord, it crushed the insulation and eventually during a heavy storm got in the water and destroyed about 6 foot of the cord, one of the wires was completely eaten away inside its insulation. Since dock had no ELCI it kept sending AC currents into the water for about a week while I was away. If the cord is salt encrusted on the inside or wet, its insulations been breached.

About installing ELCI breakers, since none of the local marinas that I know of have done anything, its not being enforced then by code compliance. Maybe they let them get away with it until they need to do new work. So voluntary, if they are not forcing the change yet.