Heat element & shore gfci

[cmt511]

Hello

Shore gfci questions here. Like many others I now have an issue when plugged into shore power gfci at home (I've used this same outlet for 5+ yrs and tried another circuit to confirm this outlet was good) I've gone through the process of elimination with the breakers. The Gen breaker is defiantly the issue. Trips the shore gfci every time. No other breaker trips it. I did accidentally turn the water heater breaker on with no water in the tank and the electric switch on. Wondering if the element is now bad and causing this even with the breaker and switch off? Is there still current trying to run through the element and shorting? Not sure if they are related in anyway. The water heater and gen share a dbl pole breaker. The fridge works fine. Everything works when plugged into non gfci. Any help would be appreciated! Thanks

[vermilye]

There is a video in one off there posts in the link Bud posted that has a good explanation of how GFCIs work. Around 3:30 - 3:40 minutes into the video they explain the ground/neutral fault detection circuitry.

GFCI Video

[road-runner]

enblethen wrote:
This is from Mike Holt forum

And as is so typical, the first response is yet another incorrect one, by a moderator/staff member no less. Trying to convince people that GFCIs do zero-current neutral-ground detection is an uphill climb.

The 2006 edition of UL943 includes a test for neutral-ground detection, so the requirement goes back at least that far. See section 6.7.1.2 http://www.3c-test.com/de/?m=Type&a=download&id=189

This article explains how one implementation works. The short version is that a neutral-ground fault results in the sense amplifier oscillating. https://www.powerelectronictips.com/teardown-leviton-ground-fault-circuit-interrupter/

[enblethen]

This is from Mike Holt forum

[road-runner]

duplicate deleted

[road-runner]

DrewE wrote:

Grounded neutral detection has been part of the UL specification for GFCIs since at least the 1993 edition of the spec, possibly longer. It is not a new thing at all.

What's really frustrating is it's still difficult to find a "How GFCIs work" article on the Internet that includes the grounded neutral detection. If you're trying to debate somebody who doesn't think it's true, they can find at least 10 incorrect articles that omit the neutral detection for every one you find that's correct.

[Matt_Colie]

CMT511,

Thank You for the update and confirmation.
Often when diagnoses are suggested, the op just evaporates and we never know if we were understood and if there was success.

Matt

[Bobbo]

dougrainer wrote:
This is from FLUKE corporation, Electronics tester maker. Doug

A GFCI uses a current transformer to detect the difference between the line current supplied to the load and the neutral current returning from the load. Ideally, this difference should be zero because both currents cancel. If there is a current differential, it becomes the input to a comparator within the GFCI, which changes states when the differential is around 6 mA. When the comparator changes states, it triggers a silicon-controlled rectifier, which disconnects the power from the output of the GFCI.

While that is true, it is not the only test that a GFCI does and that is not the only condition that will trip one. They did not give an exhaustive description of GFCI usage.

You are usually correct, but you need to study up a little more on this particular subject.

As a test, plug a generator bonding plug into a modern GFCI outlet and it will trip. There can be no current differential between the hot and neutral pins because nothing at all is connected to the hot pin.

[wa8yxm]

Water heater should be on a breaker all it's own
GEN(eral) can include Fridge (Does in my rig) You can simply unplug it outside it's a plug in appliance.

GEN(eral) can also describe teh GFCI chain in the RV which includes the patio outlet which can become waterlogged and make the GFCI a "Trip-o-matic" but that should be the RV's GFCI not the house one.

[DrewE]

vermilye wrote:
Part of the confusion of what capability is built into a GFCI is because the original design of a GFCI only detected the difference between the hot & neutral, but newer ones have a circuit added that detects ground/neutral faults. I don't remember the year this addition was made; I have a request at Mike Holt's forum that may provide an answer. If I get an answer, I'll post the information here.

Grounded neutral detection has been part of the UL specification for GFCIs since at least the 1993 edition of the spec, possibly longer. It is not a new thing at all.

[vermilye]

Part of the confusion of what capability is built into a GFCI is because the original design of a GFCI only detected the difference between the hot & neutral, but newer ones have a circuit added that detects ground/neutral faults. I don't remember the year this addition was made; I have a request at Mike Holt's forum that may provide an answer. If I get an answer, I'll post the information here.

[dougrainer]

This is from FLUKE corporation, Electronics tester maker. Doug

A GFCI uses a current transformer to detect the difference between the line current supplied to the load and the neutral current returning from the load. Ideally, this difference should be zero because both currents cancel. If there is a current differential, it becomes the input to a comparator within the GFCI, which changes states when the differential is around 6 mA. When the comparator changes states, it triggers a silicon-controlled rectifier, which disconnects the power from the output of the GFCI.

[wnjj]

dougrainer wrote:

Bobbo wrote:
Yep. That is THE classic cause of a ground fault. Turning on the electric element in the water heater without water in the tank almost instantly ruins the heating element. The heating element then makes contact with ground. That NEUTRAL/GROUND contact trips the GFCI every time. Your solution is to replace the heating element in the water heater. The breaker being on or off doesn't matter. The short is between NEUTRAL and GROUND, and neither one is disconnected by a breaker.

Sorry, When a Water Heater Element "Blows", there is NO CONTAC to a ground source. The Blown part looks like a small weld slag on the element. What DOES cause a GFCI to trip is the IMBALANCE of current between the Neutral and HOT. So, When the Current tries to flow thru the Heat element, the blown element causes an imbalance, of current and the GFCI sees this as a Short to Ground. I have found very few 120 Water Heaters connected to a GFCI, but it makes sense to have it connected to a GFCI. Doug

You misunderstand how a GFCI works and electricity for that matter. Current does not "try to flow" in an open circuit. The breaker was off so there is no try.

Also, a GFCI not only detects a current imbalance between hot and neutral, it also attempts to inject a small current into the neutral wire. If there is a loop formed due to a short between neutral and ground downstream (completing the loop where the neutral and ground are shorted upstream in the main panel), current will flow around that loop and get detected on the neutral but not on the hot. This is how a GFCI can trip with the hot wire completely open at the breaker. Clearly in this case there was a neutral to ground short at the element itself.

[enblethen]

Thanks for the update!

[cmt511]

Called the dealer and they were kind enough to open and sell me the element. After a little grinding to get the socket to fit, swapped the elements and all is good! Old element has a good size hole with wire hanging out. Thanks everyone for the help!

TIL. Even if the breaker and switch for the water heater are off, the element can still short and cause the shore gfci to trip.