Open Ground question

[DBECHEN]

Hi all, I have been having a problem with plugging into the shore power at our storage facility. They have all circuits run through GFCI outlets on the pole. When we plug in and we are not running anything the GFCI trips on the pole. We talked to our storage facility manager and they had an electrician come out and he said the issue was our RV having an open ground. We have a Progressive Industries surge protector that was installed by the first owner. When we plug into the 30 amp plug at our house and in campgrounds there is no problem. Any ideas what may be causing this? Thanks in advance.

[CA_Traveler]

OK if motors etc cause a GFCI to trip then they would be an impossible nightmare on 30A and 50A RV plugs.

Yikes - Yes my bathroom and kitchen counter top plugs are GFCI protected.

Sorry I just spaced out when thinking about one of my GFCI circuits. It has 8 garage and outside plugs with 270' of 14 gauge wire on a 15A CB. Not knowing this my saw wouldn't cut hot butter on the last plug. All wired to NEC and county code as I found out.

[road-runner]

The neutral-ground detection in GFCI outlets has moved on from signal injection. At least some of the ICs now being used employ a second transformer around the hot and neutral wires. A downstream neutral-ground fault creates a coupling between the two transformers, creating a feedback path that allows an op-amp inside the IC to oscillate. When the oscillation amplitude crosses a defined threshold, the IC tells the solenoid to trip the latching contacts. The technique measures resistance, and the trip threshold is nominal 2 ohms, of which 0.6 ohms is officially allocated to the normal wiring resistance, and 1.4 ohms to the fault. UL 943 requires it to work correctly with a circuit load ranging from zero to the rated load of the GFCI.

[ktmrfs]

CA Traveler wrote:

myredracer wrote:

ScottG wrote:

Oddly, GFCI is not required by NEC for a "Trailer" 30A supply or even a RV 50A outlet.

I've often wondered about that too. Cost is around $40 retail. When it comes to residences, they now call for GFCIs and AFCIs on just about anything they can think of. The NEC code writers don't seem to pay the attention to the RV world it deserves.

My guess is that there are to many appliances like A/Cs etc that cause GFCI's to fault.

Can someone shed more light on this?

My 11 year old house has one GFCI circuit and 3 AFCI circuits. None of the dedicated 20A plugs in the house or garage have either as well as none of the 120/240V circuits.

I'm suprised your bathroom outlets aren't on a GFI, likewise for Kitchen.

Not sure about 11 years ago, but
NEC code in the past and maybe currently, allow fridge and freezer circuits to be non GFI even if they are in a location requiring GFI circuits. E.g. kitchen. the solution is to use a regular breaker with the first outlet going to the fridge/freezer and then install an outlet GFI on the next outlet in the circuit.

and yes, motor driven devices are known to trip a GFI due to inductance to ground. that's why the exception for fridge and freezer.

although I believe current NEC requires all outside outlets, bathroom outlets, and kitchen outlets be protected by GFI. It may even now extend to garage and laundry rooms. Bathroom and outside outlets were required by NEC to have GFI protection at least as far back as 1978 when we built our house. Kitchen GFI requirements were added after that.

But local codes vary as well and don' always follow NEC.

AFCI's are currently requred in all bedroom outlet circuits IIRC.

given the low cost of outlet GFI's and the benefit, in our house I have upgraded all our outlet circuits to GFI's. easy to do.

One warning, a GFI will NOT prevent all possible electrocution hazards. For example if I have on rubber soled shoes on dry surface and get across the hot and neutral with both arms, good chance the GFI won't trip. In this case there likely would not be enough leakage current to a ground to cause an imbalance.

[enblethen]

A RV power source is considered a feeder circuit and not a branch circuit.
Within the RV past the 120 volt electrical panel is the branch circuit. Certain branch circuit must be protected by a GFC breaker or a GFCI receptacle.

[CA_Traveler]

myredracer wrote:

ScottG wrote:

Oddly, GFCI is not required by NEC for a "Trailer" 30A supply or even a RV 50A outlet.

I've often wondered about that too. Cost is around $40 retail. When it comes to residences, they now call for GFCIs and AFCIs on just about anything they can think of. The NEC code writers don't seem to pay the attention to the RV world it deserves.

My guess is that there are to many appliances like A/Cs etc that cause GFCI's to fault.

Can someone shed more light on this?

My 11 year old house has one GFCI circuit and 3 AFCI circuits. None of the dedicated 20A plugs in the house or garage have either as well as none of the 120/240V circuits.

[ktmrfs]

DrewE wrote:

ktmrfs wrote:

enblethen wrote:
Turning off breakers or on will not show a GFCI issue as breakers do not open ground or neutral leads. You must physically open that portion of the system. Problem could be any where in the 120 volt AC system.
Refer, water heater equipped with 120 volt AC element or converter would be places to start.

wrong, wrong wrong. opening a breaker will tell you if a given circuit has a ground fault, if the hot lead is open, which it is when the breaker is tripped, then there is no current flowing and no way to trip the GFI for a current imbalance in that circuit. close the breaker and if it trips the GFI then there is a ground fault in that circuit. So, it's a way to find which circuit has an imbalance.

If the GFI trips with an open breaker downstream, then the GFI is telling you there is a ground neutral bond in the ciruit.

so in the case of the OP, breakers are a good way to isolate the problem within a circuit.

GFCIs have grounded neutral detection in addition to the current imbalance detection and will trip on either fault. That is, they detect when the neutral and ground are connected and trip even if there is no load applied. (They do this by injecting a small common-mode signal on both the hot and neutral lines. If the neutral is grounded, some of this signal on it is diverted to ground and an imbalance exists to detect.)

agreed. that's why I pointed out If the GFI trips with an open breaker downstream, then the GFI is telling you there is a ground neutral bond in the ciruit. circuit doesn't need to be hot downstream to trip on a ground/neutral bond. it will trip an upstream GFI either way. any downstream circuit must be hot for a GFI to trip on a current imbalance.

In most cases there is NOT a downstream breaker on GFI circuits, or most circuits for that matter, so it can be hard to distinquish between a ground/neutral bond vs a current imbalance.

So an RV protected by an upstream GFI poses both challenges (fault could be on one of many circuits) and advantages, (easy to determine if it is a ground/neutral bond or current imbalance).

[DrewE]

ktmrfs wrote:

enblethen wrote:
Turning off breakers or on will not show a GFCI issue as breakers do not open ground or neutral leads. You must physically open that portion of the system. Problem could be any where in the 120 volt AC system.
Refer, water heater equipped with 120 volt AC element or converter would be places to start.

wrong, wrong wrong. opening a breaker will tell you if a given circuit has a ground fault, if the hot lead is open, which it is when the breaker is tripped, then there is no current flowing and no way to trip the GFI for a current imbalance in that circuit. close the breaker and if it trips the GFI then there is a ground fault in that circuit. So, it's a way to find which circuit has an imbalance.

If the GFI trips with an open breaker downstream, then the GFI is telling you there is a ground neutral bond in the ciruit.

so in the case of the OP, breakers are a good way to isolate the problem within a circuit.

GFCIs have grounded neutral detection in addition to the current imbalance detection and will trip on either fault. That is, they detect when the neutral and ground are connected and trip even if there is no load applied. (They do this by injecting a small common-mode signal on both the hot and neutral lines. If the neutral is grounded, some of this signal on it is diverted to ground and an imbalance exists to detect.)

[enblethen]

The neutral and ground is common through the 120 volt electrical system. It is not isolated to a particular circuit. They are all tied together, neutrals on a neutral buss, grounds on a ground buss. From the rig they remain separate back to the electrical service panel where they are tied together by the main bonding jumper.

[wnjj]

enblethen wrote:
The "leakage" between ground and neutral will be present at any time.

Not necessarily. Consider a simple heating element normally connected between hot and neutral, insulated inside a metal box that is bonded to ground. Now let’s say the element broke free from the neutral and fell against the case. Now there is no connection between ground and neutral and there will only be a current mismatch between hot and neutral if the breaker is on.

[ktmrfs]

enblethen wrote:
The "leakage" between ground and neutral will be present at any time.

there will still be a leakage path, but there is only current flowing when the circuit is completed. open the hot side and the upstream GFI cannot see any any current flow.

ground and neutral will not have current flow between them since there is no way to complete a path UNLESS there is a connection to another hot ciruit. which is a no no and unlikely or if there is induced current from another circuit. but both of these are highly unlikely.

[ktmrfs]

enblethen wrote:
Turning off breakers or on will not show a GFCI issue as breakers do not open ground or neutral leads. You must physically open that portion of the system. Problem could be any where in the 120 volt AC system.
Refer, water heater equipped with 120 volt AC element or converter would be places to start.

wrong, wrong wrong. opening a breaker will tell you if a given circuit has a ground fault, if the hot lead is open, which it is when the breaker is tripped, then there is no current flowing and no way to trip the GFI for a current imbalance in that circuit. close the breaker and if it trips the GFI then there is a ground fault in that circuit. So, it's a way to find which circuit has an imbalance.

If the GFI trips with an open breaker downstream, then the GFI is telling you there is a ground neutral bond in the ciruit.

so in the case of the OP, breakers are a good way to isolate the problem within a circuit.

[Harvard]

enblethen wrote:
The "leakage" between ground and neutral will be present at any time.

Yes but the magnitude of the neutral to ground leakage will be much less then the hot to ground leakage because the neutral to ground voltage is "near" zero.

[enblethen]

The "leakage" between ground and neutral will be present at any time.

[myredracer]

wnjj wrote:

enblethen wrote:
Turning off breakers or on will not show a GFCI issue as breakers do not open ground or neutral leads. You must physically open that portion of the system. Problem could be any where in the 120 volt AC system.
Refer, water heater equipped with 120 volt AC element or converter would be places to start.

Generally true but there could be a device that only leaks current to ground when powered up and flipping breakers is simple to try as a first shot.

Your point is precisely why some have suggested unplugging the fridge to eliminate the heating element.

Which is why I said start by turning breakers off. If that doesn't come with anything, then time to dig deeper...

[wnjj]

enblethen wrote:
Turning off breakers or on will not show a GFCI issue as breakers do not open ground or neutral leads. You must physically open that portion of the system. Problem could be any where in the 120 volt AC system.
Refer, water heater equipped with 120 volt AC element or converter would be places to start.

Generally true but there could be a device that only leaks current to ground when powered up and flipping breakers is simple to try as a first shot.

Your point is precisely why some have suggested unplugging the fridge to eliminate the heating element.