GFCI for Washing machine

[GoldDigger]

Most of the intent of GFCI protection is dealing with cord and plug connected where it is more likely that the EGC path would be compromised as compared to hard wired equipment.

Or, of course, for two wire cord and plug connected equipment like lamps, coffee pots, toasters, and double-insulated tools where there is no EGC path in the first place.

 

[kwired]

Or, of course, for two wire cord and plug connected equipment like lamps, coffee pots, toasters, and double-insulated tools where there is no EGC path in the first place.

Not so much for those items, though there is additional protection. Those items do not have metal frames that are likely to become energized, or if there is exposed metal it is isolated from being a very high risk of becoming energized so an EGC in the supply cord of those items would essentially do nothing anyway.

 

[hurk27]

Not so much for those items, though there is additional protection. Those items do not have metal frames that are likely to become energized, or if there is exposed metal it is isolated from being a very high risk of becoming energized so an EGC in the supply cord of those items would essentially do nothing anyway.

Lamps and double insulated tools I agree with you on, but toasters and coffee pots was the very reason GFCI's were added to 210.8 for kitchen counter tops, as these were a big source of shocks in a kitchens, as well as electric frying pans, and toaster ovens.

These older appliances were still very common to be in use even today I see one every once in a while and I still see them at yard sales.

Toasters were the main item brought up in many IAEI meetings as they seem to pose the most danger of the element touching the metal side of the case after the wife tries to get that piece of toast that broke off out with a table knife, when I was younger I don't know how many times I got shocked from our toaster when I touched something else like the stove or sink, my dad would just pull the plug and turn it around and plug it back in as it wasn't even polarized, I think I remember it was a Sunbeam toaster, older coffee pots had a chance of the element going to grounds as well as the deep fryers or other heating appliances, we had a toaster oven we would get shocks from also.

Most modern appliances don't have this problem as the heating elements are more insulated from the metal case if any metal is in the case, or has a 3-wire cord and plug.

If you have a kitchen appliance with over a 2' cord, its older then 1969 when they limited all kitchen appliances to 2' cords

 

[S'mise]

Funny you should ask, and the answer is no.

Believe it or not, putting a MOV across the contacts on the timer that controls the solenoid drains the surge off much slower and doesn't cause the imbalance that the surge causes, I have played with a few caps that results in the same effect or better.

To understand the reason why inductive kick back causes cheap GFCI's to trip goes back to the time when GFCI's were first coming out, even as late as the mid 1980's many manufactures didn't put much filtering to filter this spike out as well as the small time delay that today the chip in a GFCI looks at the imbalance before taking action, this time delay was the most effective way to stop most inductive trips as the speed of the spike was very short duration and had a fast rise time and decay, this put a high frequency ring into the load side of the GFCI that since it would be out of sync with the 60hz it would cause a current to develop in the sensing coil (current transformer) of the detection circuit that would cause the electronics to trip the GFCI, this high frequency pulse caused by the inductive kick back is what trips the cheaper (China made) or older GFCI's but this pulse last a very short period in time, and the National Semiconductor LM1851 chip found in most newer and better made GFCI's including breakers has the gated delay set to the max that UL specs allow which I think is 25ms which is about a half of a cycle at 60hz but is effective for most type of inductive kick backs.

It is hard to design a LC circuit to filter out this high frequency pulse because the LC circuit would have to be design where it doesnt place the dump current on the load side of the GFCI, it's not the high voltage spike that one might think is the problem and is why the MOV has little effect on the problem, it is the high frequency of the spike that is the problem, and is the same reason why many of the newer florescent lights that use 25hz to help light the lamp can cause problem if the GFCI manufacture doesn't include any filtering for these higher frequency loads.

A near by lightning strike which is also a high frequency event can also trip GFCI's even if it doesn't damage the GFCI, I have come home a couple of times after a storm has gone through to find that most of my GFCI's are tripped, but the reset and test just fine only to find out later that lightning had struck a tree a couple doors down.

Attached is a good paper on GFCI's the goes into a little about the problem with HF, but if you click on the links to the LM 1851 chip you can read a little about the gated delay in the specs.

Interesting paper. But, even if the dump current is put on the load side of the gfci, the current should still be even on line/neutral and therefore not trip the gfci. Right? I think its more of an RF type interference that trips the circuit. It just seems to me that designing a snubber ought not be that hard to figure out, either across the inductive load or the gfci itself.

 

[gulkhan123]

First thing is you most likely have a fault condition in the washer and the GFCI is just doing what it is supposed to do. Unfortunately it is hard to convince appliance repair guys something is wrong if the thing actually runs and does what it is supposed to do, so you may have to find the problem yourself. Haven't had to do so with a washer but have with refrigerators and freezers a few times. Defrost timers and elements like to sneak up on you but are not on all the time so the problem is not that obvious. Look for something in the washer that is not necessarily on all the time but is on later in a wash cycle.

Second thing is all the exceptions from GFCI there were a few years back are all gone. No more dedicated non GFCI protected receptacles in places that otherwise required GFCI like there used to be. Even if you are only on 2008 NEC I think they are all gone.

Comment: The explanation language given above is hard to understand for a general man, can't be in a simple language.
Sorry for my comment.

 

[kwired]

Comment: The explanation language given above is hard to understand for a general man, can't be in a simple language.
Sorry for my comment.

That language should not be that difficult for an electrical professional. This site is for electrical professionals not the general public.