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

I remember it being fairly difficult to convince guys that had their grandads crome plated drill or saw on the job site that the ground fault device was not bad. You know the suicide specials with the ground pin cut off the plug. They would trip the ground fault every time. I just don't think they all believed me when I told them the ground fault working correctly and saving their life. Maybe some of these guys just needed 10 or 15 ma of current to help push their brain impulses across some large synapses. I have heard that it is possible to kill brain cells, just don't remember how, or how I got home a few times either. Well I gotta go do the wash. Seems I can think clearer leaning against the washer, no GFI you know.

Ryan,

I'm a huge fan of GFCI protection. If it were up to me there'd be more GFI's, not less.

But they do nuisance trip. Whether the nuisance is actually a hazard, at least in my mind, isn't clear.

Winnie,

You said two things that make sense to me. I'm going to add a bit to one thought.

Capacitive coupling. If you had coupling at some point on a voltage divider (the resistance in the windings of a coil create a voltage divider) you would have unequal currents at the source.

The idea of flux imbalance at rather large currents. I actually keep a GFI circuit on my desk. It's a pretty nifty set up. The area where the current is sensed is neat and symetrical and it looks like, by virtue of the design, that stray flux wouldn't be a huge issue. But it could have an effect.

Here's s pretty good technical discussion on so called nuisance tripping:
http://www.marcspages.co.uk/pq/3342.htm

Ian,

I like it and I book marked it. It's in rather plain English and also fairly detailed at the same time.

It tends to confirm Winnie's capacitive coupling.

Maybe it's just me, but I can usually see the electrical dynamics of a problem a lot easier than I can this one.

No it's not just you Physis,. There are a lot of variables at work here. But I agree that this is a good "plain english" description of the capactive coupling variable. I also think that winnies explanation of percieved imbalance due to flux leakage caused by high inrush current characteristic of inductive loads also has merit.

I'm sure it's partly because your dealing with such a tiny piece of the forces in the circuit.

Here's the perfect example of nuisance GFI trips.
Okay, True, its not truly nuisance trips, as it's doing its job, tripping when like 5ma+ of current goes through ground, but it's a result of something functioning properly that its tripping. And it sure is a nuisance..

Computer power supplies. Every single one has a RFI Filter on the incoming power PRIOR to the switch. A computer can trip a gfi every time it gets plugged in. Before it even gets switched on.

Now, I have a particular problem with this. I do power distribution for large LAN events (big computer parties). Whenever we have to bring in a generator, more often then not, the power distro system I get with the generator is all GFI (which makes sense, as a portable power distro system like that is normally used outdoors)(the Hubbel Spider Boxes are a common favorite)

However, In my application, obviously generator power isn't 100% clean, and obviously a little more dirty then standard home power. So the RFI filters on all the computer power supplies, do their job, and send the dirt back on ground....

I'm sure you can see where this is going... Generator Power + GFI protected power distro system + RFI Filters on EVERY SINGLE APPLIANCE plugged into said power distro system.... It can get ugly.

Now, my question is, what Can be done to avoid this? Personally, I've considered using 3-2 prong adapters and tying the ground to neutral.. however, Im sure we all know the hazard that would create if the polarity got reversed Anywhere along the line... So it's not really an option. One idiot plugs their computer power cord in backwards because they cut the ground prong off at home, and their computer becomes a big direct connection to the hot side of a 120v plug... Even with polarization, someone would find a way.... Stupidity always does.

So.. In the end, Yes, the Real answer, is get a distro system that isn't all GFI protected... but does anyone out there know of a portable large-scale generator power distro system that isnt GFI protected? I'm talking generator sizes of 150KW+

"does anyone out there know of a portable large-scale generator power distro system that isnt GFI protected? I'm talking generator sizes of 150KW+"

Many theatrical distribution systems are available both with, and without GFI's, probhably more suited to what you're doing any way. But these are supervised systems, if you don't know what you're doing you can fry some stuff up good. (pull out nuetral under load.) Not a good idea for all access type events, where poeple just walk up and plug in. And first sign of inclimate wheather means it gets shut down. Almost makes sound like a GFI is a good idea huh?

yeha, these are open-access, 300+ person type events... the largest of which is just a little over 3000 people... but thats normally done by GE, and I just represent the house side of the project for that. they handle the main distro with their own equipment.

so the search continues...