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Is this a bad idea? Or a very useful?
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cybermaus:
So below is a "Portable Emergency Stop"

Basically where I live, central house installation GFCI are mandated since the 80ies.
Meaning they are the first thing in the breaker board, even before the breakers themselves, protecting the whole house.

So this simply triggers a ground fault. (with some diodes and caps, rather than merely a resistor, for technical reasons, but let's focus on the concept)

What would be the use case:
- When doing DIY, if things go wrong, someone else can press the emergency stop, without getting close to the out of control device.
(also applies to people doing lichtenberg wood burning and other MOT related stuff. Someone else can turn it off remotely, but not as far remote as having to run to the breakerbox)

My use case
- I have a brand new (to me) 1950 Lathe, and it did not come with an emergency stop
- Then I realized my drillpress, also did not have one. Nor my benchgrinder (Also none of my handtools, but those simply need to be released to stop.)
- Maybe I am simply getting old. Seeing danger where I used to see opportunity and excitement.

Possible drawbacks:
- There usually are 2 or 3 GFCI circuits, make sure it's connected to the correct one.
- You'll also be sitting in the dark (some countries smartly mandate separate lighting circuits, but not here in NL, lights and power are typically the same circuit)

Fraser:
I have test gear that is used to deliberately trigger the earth leakage protection on an installation as part of its commissioning tests. I suppose your device emulates such a test equipment so in terms of its safety, it may well be safe to use BUT……..

When it comes to safety systems, it is best to keep them as simple and effective as possible. The KISS principle applies. A ‘Kill’ switch should act on the appliance that it serves and should not be reliant on other systems that may, or may not, be functioning correctly at the time of need. I would not approve the use of your device in a workplace but what you do in your own home to your personal equipment is your own business, and risk. Whilst the device will likely serve your desired function, it fails the KISS test and so I recommend that you fit the correct ‘kill’ switches to all equipment/power distribution that would normally require such.

Fraser
ebastler:
Depending on how your mains wiring is arranged, the forced ground fault might also turn off the lights, your VOIP phone router etc. Not what you want in a "panic" situation.
Infraviolet:
Too easy that the thing you want to stop might be on a separate circuit, or one without a GFCI/RCD (I'm fairly sure in the UK a majority of plug sockets are on circuits without ground fault protection, I think it might only be for circuits to bathrooms, kitchens and a few other specialised places for built-in electrical devices). This idea looks like a false sense of security coupled with cutting off all manner of thngs you don't want to stop at the same time. An e-stop extension lead for the specific thing that might need stopping makes much more sense.
m k:
Our system has safety relays, usually 24V operated and independent open/close loop operated.
There the operation goes so that emergency stop opens the loop and missing 24V releases the power contactor somewhere.
So the wall is still live and somewhere in the machine the power is still present.
Machine can also be an area, so that other areas are not affected.
So the primary operation is first stop and then save.
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