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-   -   Shore GFCI trips when plugging in boat (http://www.sailnet.com/forums/electrical-systems/99907-shore-gfci-trips-when-plugging-boat.html)

rmeador 05-27-2013 01:21 PM

Shore GFCI trips when plugging in boat
 
My boat is on the hard right now for a bottom job. The yard provides power in the form of a standard household 15A outlet with GFCI. Whenever I plug my boat into it, either the GFCI trips or my main AC breaker trips. At first I thought it was too much current so I shut everything down except the charger and turned the charger to 2A. No dice. If I turn off literally every circuit then the main breaker and GFCI remain on, but that's not very useful. I never have trouble with marina shore power. Thoughts?

n8kraft 05-27-2013 11:34 PM

Two separate problems
 
You have two separate problems, and maybe a common fault. Input power GFCI outlet tripping offline is caused by different current on the hot and neutral wires going to the boat. To rule out a problem with the outlet plug in a regular household 3 prong tool instead of your boat and see if it works.
Since your boat main circuit breaker sometimes trips that indicates an overcurrent condition somewhere in your boat. There may be a short somewhere between hot and ground and neutral that causes the boat breaker and gfci to trip.

ebs001 05-28-2013 02:46 AM

Re: Shore GFCI trips when plugging in boat
 
Quote:

Originally Posted by rmeador (Post 1035985)
My boat is on the hard right now for a bottom job. The yard provides power in the form of a standard household 15A outlet with GFCI. Whenever I plug my boat into it, either the GFCI trips or my main AC breaker trips. At first I thought it was too much current so I shut everything down except the charger and turned the charger to 2A. No dice. If I turn off literally every circuit then the main breaker and GFCI remain on, but that's not very useful. I never have trouble with marina shore power. Thoughts?

When you turned everything off except the charger you said "no dice". You then turned off the charger and all was fine (I make this assumption since the charger was the only thing that was on when you said you literally turned off everything). Then your charger has a ground fault.

To verify this start with everything off, then turn on one circuit at a time turning off the first before you try the second and see when or if the GFCI trips.

You said that the main tripped? You can check that out as well by using a similar method. This time turn on the circuits one at a time as above only don't turn them off before proceeding. Note if you have an electric hot water tank it must have water in it or you will fry your HW element. Do you have an electric HW tank and if so does it have water?

rmeador 05-30-2013 11:37 AM

Re: Shore GFCI trips when plugging in boat
 
This is now a moot point, since my boat is back in the water, but I'd still like to know what was going on. The outlet worked fine for other people using it, and I also tried multiple outlets, so I don't think that is the problem. My hot water heater is AC and did have water in it, but it was turned off -- everything was off except the charger. Now, the charger is a charger/inverter, but I had the inverter function turned off. The manual does mention that it connects neutral and ground on the output side when running in inverter mode. There is no unexpected electrolysis on my boat (the zincs look fine), so I feel like a ground fault is unlikely. Perhaps it's just some brief moment of the inverter connecting neutral and ground when first powered on? There is absolutely no way there was an overcurrent condition, unless it was capacitor inrush upon initially powering the charger/inverter. I had the charger configured to 2A output and all other circuits, AC and DC, were off.

When I went to move the boat back home, the engine wouldn't start. I discovered a very loose connection from the battery bank to the engine ground point. It was apparently good enough to run all the electronics, but couldn't pull enough current to turn over the engine. Is there any possibility this was the culprit? I don't see how, seeing as it was the DC system.

Thanks for your ideas so far!

miatapaul 05-30-2013 04:19 PM

Re: Shore GFCI trips when plugging in boat
 
Actually I don't think it is a "moot point" unless you can determine it was in fact the land plug that was at fault. Electrical is the number one cause of boat fires, and if I had to guess chargers are one of the top causes if not the top cause. Gilfstar's are nice boats, but quite old now. If the electric has not been redone top to bottom by now then it is time to start thinking about doing it. Your not too far from Maine sail, perhaps he could do the rewire for you, as he seems to do an incredible job.

ebs001 05-31-2013 08:36 AM

Re: Shore GFCI trips when plugging in boat
 
When dealing with a GFCI you are talking milliamps. Somewhere around 5 milliamps leaking to ground will cause the GFCI to trip. If no one else had a problem with the GFCI receptacle then it has to be your connected load which is at fault. As I stated above it seems that your charger is the problem. Even though your inverter function is turn off the grounded neutral may not be disconnected and that is sufficient to trip the GFCI. That should be checked out and changed. When connected to shore power without GFCI protection the ground fault will not show up as a problem. It is however a violation of the electrical code since the neutral may only be grounded once. Since the supply neutral from the shore power is already grounded by grounding in the inverter you have grounded the neutral second time. This is not a problem when you are not on shore power and are operating on inverter alone. The second grounding of the neutral has the potential of tripping your boats main breaker. Although rare, it can happen because your neutral is caring the unbalanced load which can be in excess of the breaker capacity.

rmeador 05-31-2013 11:57 AM

Re: Shore GFCI trips when plugging in boat
 
Much of my boat's electrical system is original (or at least old), but it appears to be in good shape. The boat was surveyed only 2.5 years ago, and I've also done a decent amount electrical work to improve it (I'm an electrical engineer). There was a permanently installed bridge between neutral and ground in the electrical panel, but I removed that at the time I installed the inverter for exactly the reason you mentioned. I verified with a meter at that time that there were no other connections between those lines. If there is something going wrong in the charger/inverter, it must be only when it is turned on, and likely very brief. The inverter supposedly only connects neutral and ground when it is actually inverting, it disconnects them when it is passing through shore power, per the electrical code. I'm at a loss to figure out how to diagnose this, since there is no bridge when it is powered down, and in either shore or inverter powered configuration, there's supposed to be a bridge (it's just a matter of where, which a meter can't tell me).

The yard owner reported that these GFCIs are extremely sensitive and many people have trouble with them. That doesn't mean they're broken, just difficult. Also, none of the GFCIs within my boat ever trip... I'm not sure if they would if the fault is upstream of them though.

eherlihy 05-31-2013 12:09 PM

Re: Shore GFCI trips when plugging in boat
 
The GFCIs downstream of the fault would not trip.

You may be able to troubleshoot this with a DVM that captures the maximum reading. An O-scope would be even better, but probably not at your disposal. Look for any AC voltage reading between AC ground and neutral at the inverter/charger when it is off, then test again when you turn it on. Run this test again looking for DC voltage.

rmeador 05-31-2013 12:27 PM

Re: Shore GFCI trips when plugging in boat
 
I do have an oscilloscope (and a logic analyzer, not that it's useful for this -- I'm an electrical engineer!). Are you suggesting that the absence of a voltage between ground and neutral will indicate a ground fault? I can't quite figure out what you're getting at. There is always a voltage present between those two lines any time a circuit is under load due to the resistance in the wires. Any other boats on my dock drawing power will result in me seeing that voltage even if I am not drawing anything. I suppose if those lines are shorted inside my boat, I might not see a voltage. Or do you mean when inverting only (no shore power)?

ebs001 05-31-2013 01:03 PM

Re: Shore GFCI trips when plugging in boat
 
rmeador, you are somehow getting leakage to ground and from your previous description it appears to be only when you have the charger on. GFCIs are very sensitive, albeit some more than others but all within a 5 milleamp range. With a multi meter while disconnected from shore power and with only the charger turned on, you should see some continuity between the neutral and the ground. Is the inverter manually disconnected from the ships power or is it automatically disconnected when shore power is connected?


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