ECN Forum Forums Code Related Discussion NEC & other Code issues GFI / washing machines

Can you point me to an item that does produce this inductance tripping?

I see some fairly large pool pump motors running fine on GFCIs.

I don't find GFCIs tripping nearly as much as some claim.

The NEC handbook claims the nuisance tripping associated with refrigerators on GFCIs had to due with leakage current in the electric defrost circuits. They also claim this has been addressed by the manufactures.

Bob

I'm just explaining the theory of nuisance tripping due to inductance, not claiming that it is common. In fact I rarely see it associated with standard household appliances. I work in an industrial enviornment and I do see it occassionally. In fact just the other day I ran into it. One of the labs had supplied an X-Y stepper motor positioning table which also contained flourescent lighting via a GFI. With this load the GFI did not stand a chance, tripped constantly and there was NO leakage to ground. This was classic inductive load nuissance tripping. Nuissance tripping due to actual leakage current to ground is a separate issue and I agree that most houshold appliances, motors, tools etc. have overcome this problem

Yes I have had problems with fluorescents fixtures (about 20) around an indoor pool protected by a GFCI breaker.

We split the circuit in half and used two GFCI breakers, problem solved.

In my case it was the stepper motors and drives that contributed to the tripping more than the flourescent lights (although they didn't help )
Because the intent was to provide leakage current protection for the equipment and not personell, we were able to substitute a Class B GFCI device. Used an ELCI (Equipment
Leakage Circuit Interrupters) - Problem solved.

I seem to remember our NEMA rep stating that washing machines are now manufactured to specifically not trip GFCIs. I have an older washer (10years) on a GFCI of the same age, and it has never tripped while running.

PS. It was my wife's idea to put a GFCI for the washer. I told her that it was not required by code, but you know how that goes............

Rick Miell

I'm starting to think maybe I'm farther off than you are Bob. When Electric Ian mentioned inductance I started thinking Kirchoff's current law and it just doesn't seem to wash.

I'm at a loss. Why isn't there some kind of authoritative study or report on the whole issue by now? Or is there?

Mr Kirchoff says current will be the same if there is no other path. Inductance will make current lag voltage but the current in and out will be equal at any given instant ... minus leakage.

Things that trip GFCIs leak current.

And I can't see leakage being caused through induction, which is what I'm inclined to suspect, because the coil doing the inducting should have equal current on it's leads.

I agree with Bob 100%. Bob and I have argued the same point at several sites and have always always agreed.

Regarding washing machines: The will be required in the 2005 to be protected if they are within 6' of any sink. Bob mentioned the 2002 text, but the 2005 is different in 2 major ways:
1) 2005 applies to all sinks, not just wet-bar.
2) 2005 applies to all receptacles within 6' of the sink, not just those receptacles serving the countertop.

Also, the 2002 (and 2005) requires protection for all 125V 15 and 20A recpetacles in a commercial kitchen. There are certainly inductive loads in a kitchen, but I haven't heard of any nuisance tripping since the requirement.

Regarding current leakage: In my opinion, those who posted above saying that devices tripping GFCI's have leakage current are exactly right. Read the ROP/ROC to the 2002, and pay close attention to Mike Johnston (CMP 5)'s substantiation to get 210.8(B)(3) into the code. You want a body count?...read what he has to say. The reason there are no exceptions in the commercial kitchen rule is that one of the dead bodies in Mr. Johnston's case study happened because of a refrigerator with leakage current on the case...enough to kill a man. This man was mopping the floor of a commercial kitchen when he slipped on the water. In an effort to keep his balance, he grabbed the metallic handle of the fridge, and it was the last thing he ever did. He left a family behind.

So, if people what to talk to me about nuissance tripping, I say get a new appliance before it injures someone, or worse...

Just my two cents

The only time I ever personally encountered 'nuisance' tripping was on a commercial food processor in a co-op where I would cook. This was a small beast that used a 1/2 hp induction motor in its base (rather than the more common brush universal motors). It would trip the GFCI receptacle every 3 or 4 starts....then one day just after I'd pureed some soup and cleaned the machine up, it simply turned itself on and smoke started coming out of the base. It turns out that the waterproof boot on the main switch had cracked, and enough liquid had gotten in to short past the switch. To this day I don't know if it was in fact nuisance tripping, or leakage around the switch.

Regarding inductive loads and current balance: If you think of an ideal inductor isolated in free space, there is no way that more current could flow out on one leg than return on the other leg. But in this case the inductor is _not_ isolated in free space, and is not ideal. In particular there is capacitive coupling to ground all around the circuit. I would expect _some_ imbalance current caused by this capacitive coupling, since the two terminals of the GFCI are now part of several pretty complex circuits.

However I suspect a different issue. A GFCI is supposed to trip on current imbalance. However what a GFCI really does is measure the current induced in the secondary of a current transformer with all of the conductors being tested fed through the aperture. If the conductors don't equally couple to the transformer (leakage flux through the air rather than through the core), then even with perfect current balance, there will be some residual current measured detected by the transformer. I suspect that the inrush current to many inductive, or the starting current for many motors could create a total balanced current that is high enough to cause an false imbalance reading.

-Jon