Help with strange GFI issue

[O C Diver]

My guess is that the issue is in the stove and that the marina has a lower value trip from power leaking to ground. I would expect the stove to work ok when you return to your home slip.

As to what is causing the trip in the burner or burner control, I think it's going to be a proximity problem between the coil and stove frame that leaks just enough millivolts at the highest setting. Clearly the stove was built before the lower millivolt standard was in place.

As a curiosity, do you have a galvanic isolator between the shore power inlet and the main breaker panel?

Ted

 

[sunchaser]

My guess is that the issue is in the stove and that the marina has a lower value trip from power leaking to ground. I would expect the stove to work ok when you return to your home slip.

As to what is causing the trip in the burner or burner control, I think it's going to be a proximity problem between the coil and stove frame that leaks just enough millivolts at the highest setting. Clearly the stove was built before the lower millivolt standard was in place.

As a curiosity, do you have a galvanic isolator between the shore power inlet and the main breaker panel?

Ted

Good points, remembering to check current flow at incoming.

But, it is a very old stove. Possibly the burner coil and or rheostat are BO as the stove innards heat up. Before you re-wire the whole boat assess the problem child.

 

[rslifkin]

I honestly don't know if this boat has a galvanic isolator on the shore inlets. I've been meaning to check that. There's a good chance it doesn't, as it probably wasn't a factory installed item and the 120v electrical is pretty untouched other than inlets and outlets having been replaced.

As far as the 4 wire power source at home, yes, the neutrals from the boat would get combined in the splitter before they hit the pedestal. Once I see how it behaves at home, it's time to confirm the neutrals are properly isolated for the 2 inlets, then crack the stove open and start poking around.

 

[STB]

For the curious, attached is a time-trip curve for a 30amp double pole breaker not unlike thise I've seen at many marinas. Notice how long it can take to trip at modest overloads. All thermal vs magnetic breakers are like this (many breakers are a combination to trip fast above a threshhold).

 

[ScottC]

I had a look at this chart. It's enough to make me NOT curious ;-)

 

[STB]

This is one for a random cooper bussman breaker. It is a bit more user friendly.

 

[SteveK]

Have you left the cable feeding the AC unplugged while turning on the stove?

 

[rslifkin]

Have you left the cable feeding the AC unplugged while turning on the stove?

I have not tried that. Also didn't try turning the ACs off.

 

[bayview]

Two 30A cords? Switch them and see what happens.

 

[psneeld]

This was passed along to me....


You might want to pass this along.


It is common for magnesium oxide insulated resistance heater elements to have high(er) leakage current when hot. The big clue here is it takes a few minutes before there is a GFI trip, that is consistent with decreased insulation resistance at high temperature.


Get a megger and check the element when cold and it will probably read near infinite resistance to ground.



Rick

 

[rslifkin]

This was passed along to me....


You might want to pass this along.


It is common for magnesium oxide insulated resistance heater elements to have high(er) leakage current when hot. The big clue here is it takes a few minutes before there is a GFI trip, that is consistent with decreased insulation resistance at high temperature.


Get a megger and check the element when cold and it will probably read near infinite resistance to ground.



Rick

Now that's a good thought! If I can't find anything else wrong with the stove, it might be time to replace one of the burners and see if that helps.

 

[SteveK]

Now that's a good thought! If I can't find anything else wrong with the stove, it might be time to replace one of the burners and see if that helps.

yes it is a good one, but I thought you tried each burner one by one, so they would all need replacing.
My earlier post about unplugging the AC line was to see if heat affecting a neutral added resistance and the load found an easier route on the second cord, thus creating an imbalance on the one tripping.
This thought came from the push to go to smart plugs.

 

[ScottC]

If you end up having to replace burners, Do give an induction stove consideration!

 

[sbman]

You can measure leakage current with a good quality digital multimeter and then turn on various items to see where you are at. It beats guessing by a lot. It does require inserting the meter into the path of the ground though which isn't something a lot of people are prepared to do.

Clamp on leakage meters are expensive but make it very simple to see how much if any leakage current you have.

 

[rolomart3]

This has the symptoms of the classical case of a overcurrent protection circuit breaker going "soft" at the marina pedestals or just the wrong size circuit breaker used by the marina.

 

[Steve DAntonio]

Be careful, I have had cases of ELCI leakage trips wherein the culprit is, for instance a water, heater, it has something like 23 mA of leakage current, not enough to trip the ELCI, but close. Then the HVAC kicks on and it trips, so a tech will conclude it's the HVAC and replace it, and of course the problem persists.

It would be best to measure the leakage current with each AC device before drawing any conclusions. There's a possibility the ELCI is faulty, but that's not common. Blue Sea supplies ELCI test kits at no charge to ABYC Certified Electricians.

From a terminology perspective, if the dock pedestal is equipped with a leakage detection and trip device it's usually called a GFP, and it usually is set to 30mA (although I have encountered some that are 5mA, which is impractical). If the ground fault protection is on the boat, it's called an ELCI, and it too is usually designed to trip at 30 mA (that's the ABYC Standard threshold).

GFIs or GFCIs are point of use protection, i.e. an outlet, and they are set to trip at 5-7mA.

More on the subject here https://stevedmarineconsulting.com/electric-shock-drowning-and-elcis-explained/

(In Taiwan)

 

[rslifkin]

I haven't had a chance to retest at home yet, but I'll definitely test with no other devices running to be sure. I figured killing the a/c and doing that could wait for a day that wasn't 90 degrees and humid.

 

[rolomart3]

Of course a number of contributing factors, such as, ambient conditions, ground current leakage and over current may lead to a poor diagnostic. It is still more likely that the problem is caused by an overcurrent protection deficiency than a ground fault one. I say this because of the regularity with which the interrupt was reported to occur, recognizing that ground current leakage magnitudes are more variable and more dependent on ambient conditions than overcurrent magnitudes. If not an overcurrent issue, I would investigate next ground leakege currents which is very easy to do with a multimeter and a 300 ohms resistor.

 

[Comodave]

I have 6mAmp GFIs on my home dock. When I bought the boat as soon as I plugged it in they would trip. Found quite a few issues on the boat and after replacing the main electrical panel and rewiring a bunch if stuff the 6mAmp breakers do not trip. I like the 6 mAmp since I know if I can get the boat to work on them when I go to some marina with 30 mAmp breakers I will not have an issue.

 

[Martin J]

Had a similar issue twice over the years. Solved by opening panel and tightening all shore power connections. Connections can come loose over time, the last time this happened last year had one 110ac line slightly loose on my 220v/ 50amp. Tightened and problem solved. Just not enough good connection to power stove etc as well as other things. I went right through the boat after finding the discolored slight loose / poor connection behind dist panel.

 

[rslifkin]

I finally had some time to mess with this in my home slip. Put some water in a pot and heated it on the stove (on high). Tested with all 3 burners (1 at a time). 2 of them never tripped the shore side GFI even after heating for a good bit longer than it took to trip the breaker when the original problem occurred. The 3rd caused a trip after about 2 minutes. So that makes me think the issue is the burners themselves, as someone else mentioned. I'll have to price out new elements. If they're cheap, I'll just replace and see what happens. Interestingly, 1 of the burners that didn't trip today did cause a trip when I first had the problem.

 

[rslifkin]

Total cost for 3 new burners is just under $60, so I ordered new ones. Might as well do it now, as it looks like these burners (6", 1100w, 120v) are discontinued, so at some point I won't be able to get new ones and might have to replace the stove if I need one.