GFI electrical question

[dogvetia]

I acquired a 2018 cruiser aire 28fd in October. Using it here in AZ this winter, I noticed that while using 50 amp generator power the bathroom gfi outlet which controls a couple more in kitchen area works great. When I switch to 50 amp shore power supplied thru a surge protector, this gfi outlet trips and cannot be reset. Taking the surge protector out of the system makes no difference. I installed a new 20 amp GFI outlet with same results. Since the power comes into the 5th wheel thru the same system I am stumped. Any thoughts or advice?

[theoldwizard1]

BB_TX wrote:
Get a tester like shown below and plug into a working non GFCI outlet. Then connect RV to shore power and check for correct power. Then plug RV into your generator and again check for correct power. I am thinking you will find an open ground when connected to generator.

Tester

Good suggestion, but this type of tester is not sensitive to find a GFCI problem.

[jkwilson]

My bet is you aren’t getting both legs of power when on shore power. Either the cord is bad, shore power is bad, cord is loose in the plug on the trailer or a very common failure of a bad transfer switch. Fairly easy to verify at your panel.

[JRscooby]

BB_TX wrote:
Get a tester like shown below and plug into a working non GFCI outlet. Then connect RV to shore power and check for correct power. Then plug RV into your generator and again check for correct power. I am thinking you will find an open ground when connected to generator.

As a CG host in a state park all I was allowed to do when a camper complained about power issues was plug that type tester into the post, using what adapters needed (50-30, 30-15, you know, things that can burn snot down if miss used) If the lights came on as expected, "Sorry, the issue is in your camper." Now, unless the camper was acting like Richard Noggin, I would ask if they had any outlets not controlled by GFI, and offer to let them plug my tester in. It would tell them the issue.
The breakers in your panel trip when currant flow exceeds limit. But because some things put a much larger load on for short time they will handle large load for short time. If breaker let the starting load run for long that little wire would burn up, maybe burn the house down Breaker don't know if that extra load is starting the garbage disposal, or if the maid is touching a bare wire and the faucet. In the time it takes to start the motor, the maid might be dead.
GFI, compares hot and neutral. Normal operation there is no reason for there to be a difference, so instantly stops flow.
Breakers and fuses are to protect things, GFI is to protect people.

[BB_TX]

Get a tester like shown below and plug into a working non GFCI outlet. Then connect RV to shore power and check for correct power. Then plug RV into your generator and again check for correct power. I am thinking you will find an open ground when connected to generator.

Tester

[dogvetia]

This has been an enlightening dissertation on how a gif circuit works and I appreciate all the replies but I still don't see why 50 amps coming from a post or generators and coming thru the same plug in the side of the rv should affect the bathroom gfi outlet has two total different actions. Both sources travel thru the same wiring paths so why does the gif outlet interpret them differently?

[BB_TX]

JRscooby wrote:

BB_TX wrote:

theoldwizard1 wrote:

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

This is correct. However, there must be some ground path back to the power source for the GFCI to be able to have a discrepancy between the current in the hot pin vs the current in the neutral pin. The GFCI works on the principle that that there is some current "leaking" out of the circuit. For there to be any current flowing outside the circuit in question, there must be some path for that current to flow back to the source. Electricity requires a closed path to flow. If that path does not exist, then current can not "leak" out of the circuit. In old ungrounded homes, that ground could be plumbing at the various sources of water.

That "leak" the GFI is detecting is what is running up your arm on it's way to ground. For decades, normal house wiring was only 2 conductors to outlet or lamp. There was no path to the water pipe for most uses.

Electric current requires a closed circuit, meaning a path back to the power source. Basic fundamental of electricity. In the case of utility power it means a path from hot back to earth ground or to neutral. It can’t just leak out to anywhere it wants. “Running up your arm” will only happen if you are grounded in some manner to the source or touching neutral. Standing on the ground would do it. Touching a metal plumbing pipe or fixture would do it. You can hold a live 120 vac wire if you are completely isolated from any other path to the power source.
https://www.dummies.com/article/technology/electronics/general-electronics/closed-open-and-short-cir...

[ScottG]

JRscooby wrote:

BB_TX wrote:

theoldwizard1 wrote:

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

This is correct. However, there must be some ground path back to the power source for the GFCI to be able to have a discrepancy between the current in the hot pin vs the current in the neutral pin. The GFCI works on the principle that that there is some current "leaking" out of the circuit. For there to be any current flowing outside the circuit in question, there must be some path for that current to flow back to the source. Electricity requires a closed path to flow. If that path does not exist, then current can not "leak" out of the circuit. In old ungrounded homes, that ground could be plumbing at the various sources of water.

That "leak" the GFI is detecting is what is running up your arm on it's way to ground. For decades, normal house wiring was only 2 conductors to outlet or lamp. There was no path to the water pipe for most uses.

A GFCI does not have to have a path to ground to work. It detects current flowing outside of the normal hot-neutral circuit as already described and assumes the leakage is through something else bad but it doesn't actually have to determine where it's going.

A warning on replacing GFCI's! A few years ago they changed the connection points so the old "Line In" and the "Out" were reversed on new GFCI's. If you don't look closely at what you're doing and hook the new one up exactly the same as the old parts, you can put the new one (or a whole kitchen full..) in backwards and it will be dead (but not damaged). Don't ask me how I learned this lesson..

[JRscooby]

BB_TX wrote:

theoldwizard1 wrote:

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

This is correct. However, there must be some ground path back to the power source for the GFCI to be able to have a discrepancy between the current in the hot pin vs the current in the neutral pin. The GFCI works on the principle that that there is some current "leaking" out of the circuit. For there to be any current flowing outside the circuit in question, there must be some path for that current to flow back to the source. Electricity requires a closed path to flow. If that path does not exist, then current can not "leak" out of the circuit. In old ungrounded homes, that ground could be plumbing at the various sources of water.

That "leak" the GFI is detecting is what is running up your arm on it's way to ground. For decades, normal house wiring was only 2 conductors to outlet or lamp. There was no path to the water pipe for most uses.

[BB_TX]

theoldwizard1 wrote:

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

This is correct. However, there must be some ground path back to the power source for the GFCI to be able to have a discrepancy between the current in the hot pin vs the current in the neutral pin. The GFCI works on the principle that that there is some current "leaking" out of the circuit. For there to be any current flowing outside the circuit in question, there must be some path for that current to flow back to the source. Electricity requires a closed path to flow. If that path does not exist, then current can not "leak" out of the circuit. In old ungrounded homes, that ground could be plumbing at the various sources of water.

[theoldwizard1]

Allworth wrote:
GFI needs a hard ground.

Not true !

GFI works by measuring the current flowing in and the current flowing out. It trips if they are not equal.

GFI can be used in old houses with no grounds (requires that the outlet be labeled as not grounded).

[enblethen]

My mind keeps coming back to inverter, if equipped. Feed through function.
Do you have an inverter? If yes, turn it off, then restart.
Does receptacle work on battery power through the inverter?
Try turning off all circuit breakers in the rig. Apply slight pressure toward off. Turn on main breaker, then branch breakers one at a time.
Does your rig have a detachable cord? Check connections in cord body.

[sayoung]

I was having a GFCI tripping quiet often & replaced and kept tripping. I checked the wires in panel & found the neutral on the gnd bus and the gnd wire on neutral. Swapped wires to correct bus ( these should be set up as subfeed panels ) & no more nuisance trips. Why it had not done this for 8 years since new don't have a clue. Just something to check.

[BB_TX]

Do you have more than one GFCI outlet in the RV? And if so, does it also trip?

A GFCI outlet functions by comparing the amount of current flowing in the hot pin to the amount of current flowing in the neutral pin. They should be exactly the same. A difference of around 4 milliamps will trip the GFCI outlet. That difference means some of the current flowing into one pin is not reaching the other pin, i.e. some is “leaking” out somewhere. To be leaking out means it has to be reaching the power source (generator or shore power) via a ground path bypassing the outlet. And since ground and neutral are bonded at the source, that leakage gets back to the source neutral.

This makes me wonder if your generator ground is grounded to your trailer. Or your generator neutral is not bonded to generator ground. GFCI tripping when connected to shore power indicates you have a ground fault in one of your circuits or something plugged into one of those circuits. Not tripping on generator seems to indicate no ground path back to generator neutral.

[jkwilson]

Allworth wrote:
GFI needs a hard ground.

Generator power is a floating ground. You are grounded to the generator, not the power grid.

A GFCI requires no ground at all of any form. It is perfectly fine, and a good idea, to install GFCIs in place of old two prong outlets.