GFI Shore Power Circuit Issues

[egaito]

I really missed you guys this weekend......

Took a trip over to a friends dock. They have a lot way up by the headwaters of one of the rivers that feed our lake, where they've placed a dock with shore power.

I ended up playing too long with a new toy (that's another story) and we went up at night, my favorite time to boat anyway.

So we pull up around 10:30pm, tie up, pop in the cables and throw the breaker, which immediately pops! After playing with this for awhile, I simply couldn't get the breaker to stay engaged with any type of load placed on them with two exeptions.

First was my battery charger. It was pumping out 15 or so amps of charge power, but the breaker held. The other circuit I could activate was my soloon lights. Anything else, even when activated individually would trip the breaker.

Since the boat never blows dock breakers at the marina, and is GFCI, I figure there must be something about how the boat is wired that's making the GFCI gods angry.

Another clue toward this conclusion is that the owner and her son both use the dock, sometimes together, with their '43 Chris and '39 Sea Ray. They can't pull their full load at the same time, but are able to run refridgeration, air, TV's, battery chargers....basically everything but their stoves at once.

So what could be wrong with my wiring?

I offered to change out the breaker. It's core rule to put them on residential docks, though not required in marinas here.

 

[Nonchalant1]

Do you have an isolation transformer and they don't?

Doug

 

[egaito]

Do you have an isolation transformer and they don't?

Doug

I don't have one...not sure about the Chris, but pretty sure the Sea Ray (80% confidence) does not either.

 

[Genesis]

You're leaking current to ground if the dock has a GFCI and is tripping. That's bad news - find out what's up with your wiring.

If you do not have an isolation transformer but DO have reverse polarity indicators, they can be responsible for this.

 

[qwave]

gfi breakers can become sensitive over time. only miliamps difference between neutral and power will trip the breaker. If you only have problems on that particular dock check the panel on shore. corrosion, water, loose connections etc. will give you nuisance tripping.

 

[pmurphy]

You're leaking current to ground if the dock has a GFCI and is tripping. That's bad news - find out what's up with your wiring.

If you do not have an isolation transformer but DO have reverse polarity indicators, they can be responsible for this.

How does one go about checking for current leaking to ground or a problem with the reverse polarity indicators (I don't have an isolation transformer). I've just wired up new shore power with a GFCI breaker and can't get the power to stay on. I've recently stayed at a variety of marinas without any problems, so I'm a little suspect it might be some sort of problem with my shore power install job, rather than an issue on the boat. Problem is, I've run out of things to check on my shore power install, so I guess I have to focus on the boat.
Any thoughts would be greatly appreciated.
Pat

 

[TedZ]

I love this forum.

Never dawned on me that a reverse polarity circuit could trip a ground fault breaker but i'll bet that nothing is wrong on the dock or the boat. For one thing it is not the dock or it would trip whether or not a boat was plugged in. Obviously, when you plug your boat in there is a problem, but not at all marinas. Is it a problem at the newer ones?

A reverse polarity indicator is a low voltage lamp wired between neutral and ground (earth...the conductor stuck or buried in mother earth). The conductivity through the bulb is very low but not zero. Believe it or not the unit of conductance is a mho...ohm backwards. Mhos are a very small unit of measure. Modern, as opposed to tired GFI's are sensitive to conductance but that spec is usually not published. If you want to test it, get a meter that measures conductance (most Flukes) and see what it measures with the boat not plugged in. A small conductance is not bad if you have reverse polarity indicators. If you want to go through the trouble, unscrew the bulb and see if it still trips and measure the conductance again. Should be zero. If it is not, you should find it and some wiring issue would likely be the cause. Turn off breakers until the conductance goes away.

Genesis is the one who, i believe, has got this problem figured out. I'm just explaining his find.

Ted

 

[pmurphy]

Ted-
Thanks for your input. In my case, it must not be the reverse polarity indicator, given what you said. My circumstance is rather odd. I can plug in my shore power cord with all breakers shut off. The "shore power" indicator light on the panel glows indicating such. My reverse polarity light is not lit, and don't I push the button to test it either. Once I turn on any breaker, the GFI trips.
Now comes the odd part. If I hook up a 20 amp extension cord to my 30 amp service receptacle on the boat (using adapters), I can turn on a variety of breakers without tripping the GFI built into the 20amp outlet (to 20amp GFI is different GFI from my 50amp service GFI breaker).
I don't know where to begin to trouble shoot this. I'm guessing I might have a current leak to ground and that the 50amp GFI is just more sensitive than the 20amp GFI. If that is the case, I need to know how to track down the problem and fix it.
Pat

 

[TedZ]

If you have a push the botton reverse polarity indicator it is not that.

When you plug in the 20 amp whip you are only using one leg of your boat's circuits. With the 50 amp both legs, i'm guessing you have two 30 amp plugs on a 50 amp wye. The breakers that don't cause a ground fault i'm assuming are on the ok side but you have to check that. Lots of guessing here but it sounds like the problem can be isolated to one leg.

If that is the case, look for motors etc. on that leg that have slight shorts to ground. They likely are causing the problem, which is really a process of elimination task by turning off breakers and even unwiring various devices. No fun, but what are your choices?

Ted

 

[Trojan]

You have a small leak. Adding the extension cord adds resistance to the circuit. So it won't show up. It has got to be a real small leak. Like a spider Web. I don't think your boat has 240 volt service.


BILL

 

[TedZ]

Well you need to determine that. My 43DC has two 30 amp plugs. If you plug them both in, depending on how the thirty amps were wired, you get two different 120 VAC legs and if wired in the same tower, 90% of the time they are a split 240 VAC. If you plug into 50 amp with a 50 amp to two thirty amp wye, you get 240 volts across the two circuits 99% of the time although it may not be used. But whether it is two 120's or whatever, it sounded like one leg was causing the problem. It would be nice to identify that leg and see what is wired ahead of the breakers. Isolators (not isolation transformers) for example.

Ted

 

[Trojan]

You will (should) never have 240 volts at your plug. Your system was designed for 120 volts on the same leg. Not split. Your plugs are wired for hot, neutral and ground. They SHOULD be on the same phase for safety, but they don't have to be. You can not plug into a 3 prong 50 amp plug wired for 240 volts. The 3 prong plug on your boat is not wired to work on a 240 3 prong plug. You can run 2 different legs on the 3 prong singles. You can not run 2, 3 prong plugs into a 50 amp splitter if the shore power plug is a 50 amp 240 volt receiver without letting smoke out. There was a thread on this here before. The old shore systems had 3 prong 120 volt and 240 volt in the same receiver. The new shore systems use a 4 prong plug so this won't happen. I always check the 3 prong 50 amp receiver at a strange marina before I plug in. I let the smoke out once, never again.




BILL

 

[TedZ]

I'm not following you.

Single 50 Amp 240 VAC recptacles (female plugs) are commonly split to two 30 amp 120 VAC receptacles with a wye adapter made by Hubbell, Maranco etc. If you are getting smoke from these there is something wrong. All these do is put 120 VAC on each 30 amp plug just as if you had plugged two 30 amp cords in.

If you have two 30 amp plugs in a single marina tower they are 99% of the time wired from a split 240 VAC feed. So if you put a meter lead in the hot in each 30 amp plug you will read 240 VAC. In what scenerio would anyone care?

Ted

 

[Trojan]

Ted ,That is not completely true. It all depends on how the dock plug is wired and hubble makes 2 different 30 amp twin to 50 amp 3 prong. My Y is a Marinco 50 amp 120 volt 3 prong plug. I have 50 amps with both plugs on 1 leg. It will pop a breaker if you plug it into a 50 amp 240 3 prong. I have done that, It puts the neutral hot. Not good. If you use 2 plugs then you could have 240 on your boat. One on each leg. If you use the other Y you could also could have 120 on each leg you are correct. My Y plug is new this year. Now that You got me re thinking. I find that the 30 amp 120 male plug will fit the 30 amp 240 female. But not the other way around. I think I will change that for next year. Its not likely but you could get across the two not thinking. I chose the single leg because that was the highest voltage in the marina. I don't need to worry now I changed marinas. They have good voltage and I'm on 2 feeds.

BILL

 

[TedZ]

Hi,

First let me say i realize you are very knowledgeable and have given this a lot of thought. Obviously, i could be wrong. No one has seen everything under the sun. But...

I have included the Hubbell adapter .pdf. I don't see any adapter that would take 240 VAC and split it to two 30 amp plugs and maintain 240 VAC. For the life of me i can't see why such a device would be used, but if you say it exists, good enough for me. Hope we have alerted folks to a potential problem if one has such an adapter.

Best.

Ted

 

[TedZ]

Sorry, upload doesn't seem to be working or it is pilot error!

Adapters are on the Hubbell web site very clearly marked.

Ted

 

[Trojan]

Ted that is what I thought. Until I plug it in. I turned the power selector on and wham. It maid one heck of a spark out the front of the main panel in the salon. Pegged the 110 volt meter, took out the TV. stereo, and VCR. I was lucky there was not more damage. I was dumb founded, felt real dumb as what took place. I don't have a Hubble maybe that is my problem. I have a Marinco No. 152AY. The Y I should have is 153AY. I'm going to cut the 50 amp 120 volt plug off the cable and replace it with a 50 amp 240 volt plug. So it can't happen again. I'm still learning. That's why I'm here. I can take a beating when I'm wrong and sometimes I am. There are a lot of people here smarter than me. I don't mean to step on any toes.



BILL