Is this a bad idea? Or a very useful? - Page 1
Forum section: electronics / general

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 01, 2023, 07:19:53 am
content: 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)

author: Fraser
author_rank: Super Contributor
timestamp: June 01, 2023, 07:50:11 am
content: 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

author: ebastler
author_rank: Super Contributor
timestamp: June 01, 2023, 09:08:23 am
content: 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.

author: Infraviolet
author_rank: Super Contributor
timestamp: June 01, 2023, 05:24:45 pm
content: 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.

author: m k
author_rank: Super Contributor
timestamp: June 01, 2023, 06:15:50 pm
content: 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.

author: bookaboo
author_rank: Frequent Contributor
timestamp: June 02, 2023, 04:46:58 am
content: It would have been much easier to build a relay/contactor Stop/Reset box to kill the power to the equipment. Any number of events could lead to your design not working.

author: hans
author_rank: Super Contributor
timestamp: June 02, 2023, 07:29:51 am
content: Anecdotal comment: even if you have a GFCI, the manufacturer and safety experts recommended to test that device monthly to make sure it still works normally. But who does that each month? I haven't touched (pun intended) mine in years. I assume it works.assume. But never would I make it a normal operation procedure where I rely on that protection.I think it's a risk assessment if you want to make that assumption. Because even that monthly test is not a guarantee it will work. I think the much more sensible option is to equip dangerous machinery with a real emergency stop, for example a relay box that switches the outlets to those machines.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 02, 2023, 08:05:08 am
content: ok, the consensus is clear, you all can stop now.I guess subconsciously I was doubtful myself, which is why I even posted. Sometimes we are blindsided by own own idea's@hans. Interestingly, I do test every so often. The reason probably because both in my own house when I first bought it, as well as a sisters house when she bought it, the GFCI were indeed not working.Usually whenever I need to shut off power because I am messing with an outlet somewhere, that is a good moment to try the GFCI rather then directly going for the fuse. Especially because my router and servers are on a separate GFCI anyway.