GFCI Problems

There are several types of GFCI problems that will be discussed and a technical article from Heart is also presented below.

You pull into a campground on a sunny, hot and humid afternoon. You hurry to plug into the campground receptacle so that the a/c can start cooling things off. Then, shortly after you plug in, the campground GFCI blows and you have no shore power. Now what?

There may be one of several things that is causing the GFCI to trip:

1. The campground power post may be wired wrong. ALWAYS plug in your outlet tester to ensure that the campground outlet is wired correctly. This COULD prevent costly damage the electrical equipment in your RV, a possible fire, or a possible electrocution!
2. Assuming the campground power post is wired correctly, the GFCI in the campground power post could be extremely fast-acting. So fast that the Heart transfer relay's switching causes a short-duration imbalance that causes the campground GFCI to blow. Try another campsite and see if the problem persists. Note - most 50 amp outlets do not have a GFCI, so you could try using a 50-to-30 amp dogbone to eliminate this problem.
3. You could have a problem with the wiring in your D. You will need to isolate the problem to a particular circuit. Turn off all the ac breakers and then turn them on one at a time until the GFCI blows. You can then further troubleshoot the faulty circuit to determine if the problem is an appliance or a wiring problem.

You may also have a problem with one of the GFCI's in your D tripping. This is almost always due to a faulty appliance or a wire that has come loose in the D. If it is the latter, it is VERY important that you get this fixed before using your that circuit on your D. Very rarely is the problem a faulty GFCI.

Here is the technical article from Heart Interface:
SUBJECT: USING GFCI's WITH INVERTER / CHARGERS

INTRODUCTION
GFCI's (Ground Fault Circuit Interrupters) can be used successfully on both the AC input and AC output sides of Inverter / Chargers. There are however some things to be aware of.

DEFINITION
GFCI's, also known in Europe as RCCB's (Residual Current Circuit Breakers), are designed to open an AC circuit if a significant amount of ground current is detected indicating that there is current leakage present that could present a shock hazard for people. This is known as a ground fault condition. Receptacle type GFCI's do not protect against short circuits or overloads, this is still the job of circuit breakers or fuses. Panel mounted GFCIs however include both ground fault detection/protection for a circuit and overcurrent protection. Receptacle type GFCI's will protect a whole string of outlets against ground faults if they are wired into the circuit as the first receptacle in the circuit. GFCIs are usually used for outdoor outlets and for outlets near water or plumbing such as in kitchens and bathrooms where a person is more likely to be grounded and at more risk if there is a shock hazard.

AC INPUT SIDE OF THE INVERTER / CHARGER
Some RV parks and marinas have shore cord connections that are supplied through GFCI breakers. When the coach or boat is plugged in, the whole coach/boat electrical system would be protected against ground faults. If the GFCI trips when the system is connected, it indicates that there is too much AC leakage to ground. The most common cause of this problem when it is associated with the inverter/charger, has to do with the way the inverter/charger is installed, not with the unit itself.

When installing an inverter/charger, it is important that the AC output side of the inverter feeds its own hot and neutral buses. These buses need to be isolated from the input MAIN hot and neutral buses. All the loads that are fed by the inverter need to connect to these isolated hot and neutral busses. Using one common ground bus however is acceptable. In many cases where GFCIs trip, the installer had connected the inverter AC output neutral to the main neutral bus. Since the inverter grounds its output neutral when it is OFF or inverting, If the output neutral is connected to the main neutral, the main neutral also gets grounded. A GFCI will detect this condition and trip out before the inverter has a chance to disconnect ground from its output neutral when it transfers shore power through.

AC OUTPUT SIDE OF THE INVERTER / CHARGER
Using a GFCI on the AC output side of the inverter is a common practice. The brand that Heart has tested and uses in some models of inverters is the Pass & Seymour/Legrand. Other brands of GFCIs will usually work fine. The main things to be aware of are testing of the GFCI and what can cause nuisance tripping of the GFCI.

A GFCI has a test button on it that simulates a ground fault condition to test that the GFCI functions properly. A reset button is also present. A GFCI should be tested only when the inverter is inverting or transferring shore or generator power through to the GFCI outlet. It should not be tested when the inverter is in idle mode. If the test button is pressed while the inverter is in idle mode the GFCI will appear to fail the test and the circuitry inside the GFCI could be damaged by the sense pulses that the inverter generates during idle mode.

Nuisance tripping would be defined as the GFCI holding OK on shore power but tripping when inverter power is present. This can sometimes be caused by marginal leakage between neutral and ground within the GFCI protected circuit. This marginal leakage is not enough to cause a shock hazard but may be enough to trip a GFCI when inverter power is present. This marginal leakage is often caused by surge suppression circuitry in some types of electronic equipment that may be connected to the circuit. This surge suppression circuitry sometimes includes capacitors between hot and ground and between neutral and ground. On sine wave shore power, these capacitors will not couple enough energy to ground to trip a GFCI. But with inverter power, the capacitors couple more energy due to the harmonics contained in the waveform and this can be enough to trip a GFCI.