> … it proposes to require the same exact ground-fault circuit-interrupter protection that makes you push that little button on your bathroom outlet every time the curling iron won’t heat up.
Specifically if your GFCI in the bathroom (or anywhere) keeps tripping it’s because something is wrong with your wiring or something plugged into the outlet.
It took some restraint to not use all caps in part of that sentence.
Unfortunately this is not quite true. For two-prong plugs, yes, it is 100% accurate. However larger devices with grounded plugs, especially heavier machinery, will typically contain a line filter with Y capacitors running line to ground. This shows up as a tiny leakage current, which some GFCIs will detect (because it really is leaking) even though this is a nuisance trip (because it is completely safe and normal operation). That's part of where the 30mA trip specification for certain types of non-normal-residential-circuit comes from.
Something like this?
“Though you rarely will see your bathroom GFCI trip (unless you’re dropping the hair dryer into the bath water), some kinds of larger, more complicated machinery can cause nuisance trips.”
Line filters are everywhere. They're generally required to pass conducted emissions requirements. They aren't going away soon, and our fault protection devices need to work with them, not blindly ignore how we've been meeting EMC requirements for decades.
edit: 120V is not immune. I once worked on a project involving powering equipment in a Faraday case at 120V. The mandatory filter (to prevent the wire from conducting emissions out of the cage) instantly tripped GFCI.
The right solution IMO would have been one of:
a) A better filter that doesn’t pass 50-60Hz. This is doable in theory, but I’ve never seen one.
b) A transformer or other isolated supply outside the cage, with a GFCI inside the cage (to protect the people who may enter to touch the equipment).
c) A transformer outside, not necessarily right next to the cage, supplying the inside with two opposite-phase lines at 60Vrms each. No net leakage! This would require that everything inside accept such a supply, which rules out anything that wants a real neutral.
d) I bet someone could design a transformer with a shield between the windings that would integrate with the Faraday cage. Power would couple in inductively through the shield. Common-mode RFI would have a very hard time escaping, and different mode RFI could be filtered and probably matters quite a bit less anyway.
Of course, the actual solution chosen by the site’s electrical people was rather less classy.
Of course, real transformers are not ideal. This:
> I bet someone could design a transformer with a shield between the windings that would integrate with the Faraday cage. Power would couple in inductively through the shield. Common-mode RFI would have a very hard time escaping, and different mode RFI could be filtered and probably matters quite a bit less anyway.
exists and it is called an "electrostatic shield" inside a transformer. Magnetics people do not like to make these, but they are a standard enough request that they'll do it for you and the only complaints you'll get will be from the people on your side who see the invoice. Electrostatic shields are also not perfect but they help tremendously. The shield connection usually comes out of the potted assembly on another wire so you can hook it up as required.
Protip: if you are ever trying to replace or redesign equipment that uses an electrostatically shielded transformer, do ask why they went to that effort. Don't just try to use a normal transformer and then wonder why you can't get it working right... despite man-months of effort....
Yes and no. You declare one of the secondary wires to be neutral and the other to be the “line”, and you connect “ground” to “neutral” in exactly one place. And the GFI monitors the sum of the line and neutral current, but not the ground. And you connect your equipment chassis to ground via the wire that, in the US, is green and is called, in the NEC, the “equipment grounding conductor”. And the GFCI will protect you if you are touching a grounded object with one part of your body and accidentally contact something that’s is at “line” voltage.
If you are using a transformer to provide power to part of a building subject to the NEC, you may be required to do approximately this. And your bathroom receptacles are hopefully GFCI protected and are also fed from a transformer near your house…
> electrostatic shield
You can get a transformer with approximately this, in small sizes, sold for “medical” use, off the shelf at reasonable prices. I have one that I bought from Digikey because it had the right specs, even though I don’t need the shield.
But I haven’t seen one that has fittings intended to integrate it into a Faraday cage. Maybe someone makes it. Admittedly, I have not worked with that many Faraday cages in my life, and I didn’t get to examine the detailed construction of the giant anechoic Faraday cage in which we tested the smaller Faraday cage I was using.
The NEC might or might not have something silly to say about that, but when you have a giant custom-built Faraday cage, I think most people will be understanding that you might choose to call it "equipment" (and thus, for example, claim that 61010 applies) rather than "building wiring" (so not NFPA 70).
You can also earth things in some really weird ways. My favorite was to connect the secondary to earth through a 12V bidirectional TVS diode. Apparently this stops a lot of nuisance issues while still allowing serious currents to flow. Unfortunately, you want a bigass TVS to do this, and those are rather capacitive. So you still end up with RF issues. (No, you cannot use this to make an arc fault detector. Or at least, I couldn't do it.)
Electrostatically shielded transformers are not really stock items. You will usually have to get them custom-built and they will usually end up as expensive, higher-performing C-type cores. Shoutout to Triad Magnetics for being very nice to work with as a custom magnetics vendor on that horrid project even though the project was cursed and we ended up going with someone else (which we should have known a lot earlier and not strung you guys along, but engineering and management had different aims there...), right up until it got cancelled.
Or the outlet itself. Some outlets end up false tripping, and need to be replaced. Probably happens with GFCI breakers, if that's where the GFCI is. Of course, normal breakers sometimes false trip and need replacement, too.
We have had whole-house GFCIs (or RDCs as we call them here) in the NZ electrical standards for 20 years, they seem to be pretty reliable, I've never seen them trip for without a reason.
I have seen them trip on devices that were barely faulty. Devices which worked fine on a regular outlet, but would trip a RCD.
But I've never seen an EV charger trip an RCD!
It's actually kinda easy - the way GFCIs work is pretty neat.
You pass the live and neutral through the same magnetic field sensor. So long as none of the current is escaping to earth, you get an equal current in each direction and the total magnetic field is zero.
The problem is you can get a 5mA leak to ground because of, say, condensation inside a socket. And ripping out your house's wiring in search of that is a lot of expense to deal with a relatively minor danger.
Personally I've noticed buzzing or interference with some lighting on gfci circuits.