It trips whenever hot wire gets exposed and touched by anything other than return wire. So basicaly it protects against any failure of insulation of the hot wire. At the latest when you come in contact with it in any manner.
> Curious why you’d need/want whole home gfi
Because the danger they protect against is not confined to bathrooms and the outdoors!
An RCD (GFCI) trips quickly when there is an imbalance between outgoing and returning current exceeding a certain threshold, indicating that some current is likely leaking to earth. A little more than 30mA AC through the body sustained for a couple of seconds can kill someone, but is not enough to trip a regular circuit breaker!
Wetness increases conductivity and therefore the risk of a dangerous electric shock, but a faulty appliance or damaged cable elsewhere exposing you to mains voltage can be life-threatening too!
So, why shouldn't we protect the entire house?
> I'm assuming [...] if there’s a short on any circuit power to the entire house is cut
Small nitpick: a GFCI/RCD doesn't trip because of a line-to-neutral short circuit, it only trips if some current "escapes" to somewhere else. Though it is true that nowadays we often install RCBOs which combine residual-current, overload, and short-circuit protection.
But your concern about nuisance trips is somewhat justified. If there is really only one RCD serving the entire house, which is very common for older installations, a ground fault will cause a larger outage.
Newer installations, however, typically use multiple RCBOs to reduce the blast radius. And really old installations, where small current leaks are more common, might not have an RCD anyway.
Also, in my experience, it's just not a problem in practice. I can count the number of nuisance RCD trips I've had in my life on one hand. And genuine faults are similarly rare. Other kinds of power outages are far more common.
> GFI outlets provide a very localized layer of safety [...] can be extraordinarily sensitive
I fully agree that this is an advantage.
A standard 30mA RCD or RCBO, as would be installed in Europe, should disconnect within 40ms at 150mA, but might take longer at lower currents. That could still be quite a substantial electrical shock. (I'm not qualified to say exactly how dangerous it still is, but I can attest to the fact that it can still hurt pretty bad even if the RCD trips.) A 5mA GFCI, as is typical in the US, provides a much larger safety margin. I guess nuisance trips would be a much bigger problem if the detection threshold for RCDs was lowered to 5mA.
So maybe we can agree that the perfect solution would be to have GFCI outlets everywhere? Because as it stands, you either have crude protection everywhere, or good protection limited to a few outlets.
One last note: Whether you have GFCI outlets or RCDs in your electrical panel, make sure to test them regularly via the test button! A faulty protection is no protection, and it's better to be safe than sorry.
Edit: One more thing worth keeping in mind is that, all else being equal, 230V drives almost twice the current as 120V, making the shock more dangerous and residual-current protection even more important.
Meh, gfci outlets aren’t that expensive so if you’re a super vigilant home owner you could easily put one on every circuit in your house. But modern code calls for them in the laundry room, garage, bathrooms and kitchen, so for all practical purposes you almost do have them on every circuit.
For the whole house or circuit, that’s exactly what breakers are for.
For the risk of shock from an electrified appliance, that’s what the ground is for and is a very reliable solution provided that it’s actually done correctly. Unfortunately a lot of builders and electricians cut corners and either don’t ground or don’t do it properly.
To me seems like people are hating on a pretty great system. Put differently, if all you had was a whole house GFCI and someone invented an outlet GFCI that enabled localized fault detection at very low levels it would seem like an advancement. Funny to hear people want to go backwards.
Ground does not protect against every shock hazard! Devices can fail in many ways where live parts are exposed without contacting the grounded casing. Also, imagine a little child poking a metal stick into the outlet. Now you'd better hope that outlet has GFCI. Modern code does not call for it in a child's bedroom, does it?
Edit: To be fair, modern receptacles should be tamper-resistant, but then imagine a child reaching into a lightbulb socket, or cutting through a wire, or the insulation on a wire becoming damaged, etc. pp.
> for all practical purposes you almost do have [GFCI] on every circuit
But there are still gaps! I got shocked by an old clothes iron once (and I'm glad it tripped the RCD at the panel). Bedrooms and living rooms can have electrical faults too!
Another advantage of RCD at the panel is that it protects all downstream parts of the panel and all circuit wiring too! A lot of fatalities come from people working on live wiring. (In fact, many electrocution deaths are electrical contractors.) Now sure, they almost certainly weren't following correct safety procedures, but still, a lot of them could have been saved by an RCD. Some people probably die changing their light bulbs. That's preventable by installing an RCD at the panel, so that the entire circuit is protected, not just everything plugged into a GFCI outlet.
> To me seems like people are hating on a pretty great system. [...] localized fault detection [...] would seem like an advancement
I agree that localized fault detection, all else being equal, is an advancement. But if it comes at the cost of no GFCI protection at all on other circuits, I'm not sure it's worth the tradeoff.
Hundreds of people in the US die every year from low voltage electrical shocks. This number used to be a lot higher before GFCI was common, but it likely could be lower still if GFCI was required everywhere.
Obviously it would be best to have broad coverage and localized tripping, but if I had to pick one, I'd choose broad coverage. Calling it "going backwards" misses the concern of how much is protected, rather than just how localized the impact is when there is a fault.