GFCI Question

Is the circuit a multiwire circuit?

A refrigerator should be on a separate circuit of its own with no GFCI.

GFCIs used to be notorious for tripping on motor startups, though they've gotten much better in more recent years.

Almost certainly.

Bill Ranck Blacksburg, Va.

| Have put in a GFCI wall outlet type of GFCI breaker in kitchen. | The typical type by Leviton. | | Wired it as a "feed-thru" configuration, in that it also controls downstream | wall outlets. | | The refrigerator is on one of these downstream outlets. | | The GFCI trips every day or so. | Hard to tell if it's when the fridge turns on or off, though. | Again, not all of the time. | | Question: | | Are these gadgets "notoriously fickle" and sensitive in their usage history

Some are.

| Think the fridge might be the problem, or... ?

Unlikely within the same room, but very long wire can lead to sufficient capacitive coupling to ground that the charging current itself would trip the GFCI. But that would be a rather continuous problem.

It doesn't take much current imbalance to trip the GFCI. A mere 6 milliamps leakage to ground, or a current draw that looks like it would be, would trip it.

If there is an intermittent short between neutral and ground, you would not notice such a thing in normal operation, but the GFCI would pick that up and open the circuit.

Possibly, there could be enough coupling between the start capacitor in the compressor, and the ground frame around that capacitor, that would lead to an imbalance in current, drawing just slightly more from the hot wire and returning the coupled portion on the frame ground instead of the neutral.

If you put in a separate dedicated circuit that cannot be normally reached in the kitchen (e.g. directly behind the refrigerator) I believe you may be able to avoid the GFCI requirement for that circuit. Some people have argued that putting a refrigerator on a separate circuit exposes the risk that if that circuit trips, you won't readily notice it because nothing else is on it for you to notice as not working, leading to food spoilage. OTOH, it would protect the refrigerator from other circuits being tripped by other things. If you worry about the risk of food spoilage, you could put an alarm on that circuit. A good smoke and carbon monoxide detector would generally have a power outage alarm that could beep for as long as its battery holds out. Having it plugged into the refrigerator circuit might not qualify it for the requirements of having them, but you can always add supplemental ones. Just be sure the alarm is accessible and not right next to the stove/oven.

If the refrigerator does not trip the GFCI, is it still against code to have GFCI controlled refrigerator outlet?

In new construction the refrigerator has to be on its own circuit, that's rarely the case with older houses though.

I don't think it's a code violation to have it on a GFCI, it certainly could be a problem if it's tripping all the time though. I wonder if it has an RFI filter leaking a tiny amount of current to ground.

It could be the defrosting coils. I would have to wonder if they have enough isolation to prevent GFCI tripping when they get wet.

My trips in a hydroponic application have usually been when pumps turn off.

Bill

On Wed, 14 May 2008 23:44:48 GMT peter wrote: |>

|> A refrigerator should be on a separate circuit of its own |> with no GFCI. | | If the refrigerator does not trip the GFCI, is it still against code to have | GFCI controlled refrigerator outlet?

I don't recall seeing any code section prohibiting GFCI or AFCI for almost anything you want to use them for. Certain things _require_ it, and require the GFCI at the "people protection" level, which is nominally 5ma, but must be no more than 6ma and no less than 2ma (from my recall). There may also be a requirement (if not, there should be) that if a GFCI is used, it must be wired to be in effect (e.g. don't wire it backwards to defeat the GFCI protection if the refrigerator keeps tripping it).

On Wed, 14 May 2008 23:51:12 GMT James Sweet wrote: | | peter wrote: |>> A refrigerator should be on a separate circuit of its own |>> with no GFCI. |> |> If the refrigerator does not trip the GFCI, is it still against code to have |> GFCI controlled refrigerator outlet? |> |> | | | In new construction the refrigerator has to be on its own circuit, | that's rarely the case with older houses though. | | I don't think it's a code violation to have it on a GFCI, it certainly | could be a problem if it's tripping all the time though. I wonder if it | has an RFI filter leaking a tiny amount of current to ground.

That reminds me. I've actually found that strong RF can actually cause a GFCI to trip. And worse, if the RF is sustained, apparently some models will keep on trying to trip, perhaps with the end result of letting out the magic smoke from the tripping solenoid (or worse, a lot more smoke).

The induced RF would be in common mode.

That "computes" since the opening of the circuit would cause a "voltage" kick from the induction of the windings. That higher than normal voltage is more likely to find a leakage path to ground than normal line voltage.

Sometimes they don't. We had problems with a older fridge but it's replacement never tripped the GFCI. This was an older house.

If everything is working right and you don't have water in the wrong place, I have gotten away with even dishwashers and clothes washers on a GFCI circuit. I don't recommend it necessarily but the GFCI trip might well be an early warning that something isn't quite right inside the load. When you install GFCIs in an older place, you sometimes take the decision to "protect" circuits that should be single load but aren't.

On Thu, 15 May 2008 04:07:52 -0400 John Gilmer wrote: | | |> My trips in a hydroponic application have usually been when pumps turn |> off. | | That "computes" since the opening of the circuit would cause a "voltage" | kick from the induction of the windings. That higher than normal voltage | is more likely to find a leakage path to ground than normal line voltage.

But would that kick be transferring part of its current flow back to the GFCI? If the hot wire opens (by the relay cutting off the compressor), then the kickback current would be on the neutral, but not the hot. Is that at least part of the explanation?

It is not "against the code". If the outlet is a countertop one, it is required to be GFCI protected. And in commercial kitchens all plug-in refrigerators and freezers are required to be GFCI protected.

To the OP - if you are going to post the same question in multiple newsgroups use crossposting.

This is so true. I trip the GFCI in my bathroom every time I transmit on my long wire antenna with a tuner, I have to use the vertical at the back of my yard if I run more than a few watts.. Eric

No, it's not against code to have a refrigerator on a GFCI, it's just not required on "fixed appliance" circuits. In other words, if the 'fridge is on a separate circuit of its own you don't need a GFCI and probably don't want one, though there is no harm in it. I think this exception to the general rule about GFCIs in kitchen circuits was put into the code when early GFCIs tended to pop due to motors starting/stopping. I have not seen that with newer GFCIs in many years.

As others have pointed out, this may be an indication of problems in the 'fridge causing the GFCI to pop.

Bill Ranck Blacksburg, Va.

On Thu, 15 May 2008 11:35:43 -0400 Eric wrote: | snipped-for-privacy@ipal.net wrote: |> On Wed, 14 May 2008 23:51:12 GMT James Sweet wrote: |> | |> | peter wrote: |> |>> A refrigerator should be on a separate circuit of its own |> |>> with no GFCI. |> |> |> |> If the refrigerator does not trip the GFCI, is it still against code to have |> |> GFCI controlled refrigerator outlet? |> |> |> |> |> | |> | |> | In new construction the refrigerator has to be on its own circuit, |> | that's rarely the case with older houses though. |> | |> | I don't think it's a code violation to have it on a GFCI, it certainly |> | could be a problem if it's tripping all the time though. I wonder if it |> | has an RFI filter leaking a tiny amount of current to ground. |> |> That reminds me. I've actually found that strong RF can actually cause a |> GFCI to trip. And worse, if the RF is sustained, apparently some models |> will keep on trying to trip, perhaps with the end result of letting out the |> magic smoke from the tripping solenoid (or worse, a lot more smoke). |> |> The induced RF would be in common mode. |> | This is so true. I trip the GFCI in my bathroom every time I transmit | on my long wire antenna with a tuner, I have to use the vertical at the | back of my yard if I run more than a few watts..

The hazard I found is that at least some units (the ones I had in an apartment I used to live in) would be constantly activating the trip solenoid for as long as the RF was present. So, apparently, that GFCI design did not remove AC power from the control circuitry when the contact opened. I suspect the solenoid in them is a cheap one not intended (and not tested by UL) for long continuous operation. Under such a condition, it could lose its magic smoke.

| No, it's not against code to have a refrigerator on a GFCI, it's | just not required on "fixed appliance" circuits. In other words, | if the 'fridge is on a separate circuit of its own you don't need | a GFCI and probably don't want one, though there is no harm in it. | I think this exception to the general rule about GFCIs in kitchen | circuits was put into the code when early GFCIs tended to pop due | to motors starting/stopping. I have not seen that with newer GFCIs | in many years.

How would a change in GFCI design affect this? IWSTM that it would be more about how the refrigerator was designed, assuming the GFCI was correct in the first place. But maybe the early GFCIs were 2ma and the new ones are

| As others have pointed out, this may be an indication of problems | in the 'fridge causing the GFCI to pop.

I would think so.

I argued to myself in the same way. That does not mean that I fully understand what is happening.

I have not had any trips (a few months now) since I put a 0.25µF 600VDC paper capacitor across the power terminals (hot to neutral) of the (air) pump I am using. That certainly an easy thing to try.

Bill

The GFCI does not know the difference between hot and neutral. It trips based on the imbalance of current on those two wires. A pulse on either the hot or the neutral that is not accompanied by an equal pulse on the other wire creates an imbalance that will be detected by the current transformer. If the imbalance caused by the pulse is long enough and of sufficient magnitude, the GFCI will trip.

Ed