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After working on high voltage circuits as a lineman for a couple years, and currently writing software for industrial machinery and regularly working in industr

After working on high voltage circuits as a lineman for a couple years, and currently writing software for industrial machinery and regularly working in industrial machining cabinets, I think that applying the same level of precaution used for mining to doing minor work on a 100V circuit is being a bit overzealous. To be fair, you're never going to get hurt by being superfluously safe, but at the same time I don't expect my dog is going to flip the circuit breaker on me, so I'm probably not going to resort to LO-TO when doing some minor electrical work when home alone.

taneq 7y ago
Honestly if our mains was 110V rather than "240V" (read 250-260V thanks to all of the rooftop solar in our area) I'd probably be a bit more casual about it. I've been nipped by ~100V from poor earthing and it's not that bad. 240V hurts.
- roenxi 7y ago
  I've no particular experience working with electricity so maybe you just know what you are doing - but at risk of being a know-it-all on the internet that is not a very safe approach. In an industrial setting any electricity related accident is cause for a trip to the hospital no matter how minor. For starters you don't want to be casual about 110 volts [0] and for seconds the systems that control heart rhythm use electricity. An electric shock can cause a heart to just stop some hours later (happened to a family friend as far as we can tell). It is invisible, can kill and humans don't have the right nerves for pain to be an indicator of how bad the damage is. Electricity is hazardous and work on it should leave no scope for surprises. [0] https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html https://www.asc.ohio-state.edu/physics/p616/safety/fatal_cur...
  - kozak 7y ago
    Can someone please point me to details of a biological mechanism that can cause someone to die hours after having seemingly survived an electric zap just fine? I never thought such things are possible.
    - JoeAltmaier 7y ago
      There's a term ambulance drivers use, "Walk, talk and die". For victims of car crashes that got a hard knock to the head. A brain bleed in the brain stem (if I'm remembering it right) will build up pressure until the stem suddenly disconnects. Not electrical, but such syndromes seem to be real.
      - dreamcompiler 7y ago
        It's quite real. This is why we try very hard (everything short of kidnapping) to take people to the hospital after a bad car wreck ("high energy mechanism of injury" is the term we use) even if they're walking around saying they're fine.
        kube-system 7y ago
        Adrenaline is a heck of a thing. I know someone who similarly said they were fine and wanted to go home after being hit by a car. They had fractured vertebrae and their spinal cord would have likely suffered permanent damage if it wasn’t immobilized as soon as it was.
        the-peter 7y ago
        The EMTs didn't try very hard when I was flipped by a drunk driver. I crawled out of my window and told the EMTs I just wanted to go home and they said 'ok'.
      - Cthulhu_ 7y ago
        Yup, definitely - this is why people will be asked if they blacked out, if only for a little while, after a fall. If they did the impact was severe enough to cause damage. And of course tight monitoring after head trauma.
      - tialaramex 7y ago
        Walking Ghost phase is a phenomenon in severe exposure to radiation. The patient survives initial ill effects (probably with advanced medical treatment) and now feels fine. They have no nausea, they can walk and talk like anybody else. If you tell them they're actually dying they likely won't believe you. Inside cell reproduction has stopped, and as enough cells naturally die without replacement over the next few days their systems will cease functioning and they'll die of multiple organ failure. Electricity definitely won't cause that, but yeah, humans can't sense all the terrible things that might have gone wrong with their bodies.
  - dreamcompiler 7y ago
    You're right. When I was young and stupid I did wiring repairs on 110v circuits without bothering to switch them off. I got shocked a lot, but now that I'm older and smarter I know I just got lucky.
- unlinked_dll 7y ago
  I've gotten burned by changing light bulbs without turning off the switch; garnering me the nickname "Uncle Fester" by my family (in my defense - the light bulb was out and I wasn't thinking) and that shit definitely hurts. I've also been burned debugging a power supply for a GSM amplifier used in the test harnesses for a semiconductor fab (this time was carelessness, the power supply rails weren't taped off since I was probing it attempting to find a fault on the point-to-point wiring) that was powered at 240V and holy hell I do not recommend doing anything that stupid. If it doesn't have a safe way to repair, buy a new one.
  - taneq 7y ago
    Burned or zapped? Light bulbs get thermally hot but glass is non-conductive. I haven't personally been bitten by 240V but from people I've talked to who have, I don't intend to chance it happening.
    - Qwertystop 7y ago
      I'd guess you could get zapped if you accidentally touch the metal part of the bulb (or the socket) while unscrewing the old one or screwing in the new one.
- lb1lf 7y ago
  -During the annual EE safety refresher course I take at work, the instructor makes a point of the fact that during domestic work, the electric shock is often merely the trigger for the real injury; you get zapped, then fall from the ladder you were on or whatever. (We have 240VAC mains, but I guess an unexpected jolt of 110VAC would be sufficient to make me jump...)
  - jjeaff 7y ago
    110v or 240v will kill you dead where you stand. But it's not really about the voltage. The higher the voltage, the easier it is for the electricity to ground out through you. But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. Luckily, human skin is not highly conductive and neither are rubber soled shoes. So if you are taking proper precautions and not kneeling on a wet floor while using all metal tools on bare wires when someone flips a breaker back on, then your risk is rather minimal.
    - 6nf 7y ago
      > But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. 10-20 amps? Not across your skin! Usually a 220V zap at home won't cause instant death.
      - wlesieutre 7y ago
        That's the point made in the line after your quote > Luckily, human skin is not highly conductive and neither are rubber soled shoes. Could also note that depending on your circuit breakers, a short circuit will continue delivering higher than its 20A rated capacity for some time until the overcurrent protection goes off. Thermal breakers won't react as quickly to overcurrent as thermal magnetic breakers, so it depends on what kind of protective equipment is installed. EDIT: some reference on circuit breakers https://www.se.com/ww/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/242000/FA242032/en_US/CA908024E%20(web).pdf https://www.se.com/ww/resources/sites/SCHNEIDER_ELECTRIC/con... > For example: based on the curve on page 3, an iC60 circuit breaker of curve C, 20 A rating, will interrupt a current of 100 A (5 times the rated current In) in: 0.45 seconds at least, 6 seconds at most. 6 seconds is a pretty good chunk of time for a 20A circuit to happily be delivering 100A of current.
- grawprog 7y ago
  I dunno, I got electrocuted repeatedly a few weeks ago, not sure the voltage, I was using a wet saw and didn't realize the rubber had worn out on my boots and the steel plate in the soles was touching the floor. Every time I turned the saw on or touched it when it was running I got electrocuted. It was kind of funny, nobody could figure out why i was the only one being electrocuted. All my coworkers came and touched it and were fine. But, it wasn't the pain that got to me, it was the weird feeling in my body after. All the rest of that day I felt weird. My skin felt too sensitive, my arms would twitch randomly, and I just felt kind of weak and vaguely dizzy all day. I did end up figuring it out and putting a rubber mat down which immediately stopped the electrocution problem. But I really don't like being electrocuted at all. It just isn't pleasant. On topic, all our machines get locked and tagged before opening the electrical cabinets or working on anything where you might be exposed to live wires. It's enforced by worker's comp also. We get randomly inspected fairly regularly and one thing they check is that we have lockout keys and locks on every machine breaker.
  - tomatotomato37 7y ago
    I find it interesting how you describe a job with a functional safety culture from the perspective of regulators, with lockouts and random inspections, that yet solves the issue of a power tool shocking workers at mains voltage by just tossing down a rubber mat and continuing to work with said malfunctioning tool.

taneq 7y ago

Honestly if our mains was 110V rather than "240V" (read 250-260V thanks to all of the rooftop solar in our area) I'd probably be a bit more casual about it. I've been nipped by ~100V from poor earthing and it's not that bad. 240V hurts.

roenxi 7y ago
I've no particular experience working with electricity so maybe you just know what you are doing - but at risk of being a know-it-all on the internet that is not a very safe approach. In an industrial setting any electricity related accident is cause for a trip to the hospital no matter how minor. For starters you don't want to be casual about 110 volts [0] and for seconds the systems that control heart rhythm use electricity. An electric shock can cause a heart to just stop some hours later (happened to a family friend as far as we can tell). It is invisible, can kill and humans don't have the right nerves for pain to be an indicator of how bad the damage is. Electricity is hazardous and work on it should leave no scope for surprises. [0] https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html https://www.asc.ohio-state.edu/physics/p616/safety/fatal_cur...
- kozak 7y ago
  Can someone please point me to details of a biological mechanism that can cause someone to die hours after having seemingly survived an electric zap just fine? I never thought such things are possible.
  - JoeAltmaier 7y ago
    There's a term ambulance drivers use, "Walk, talk and die". For victims of car crashes that got a hard knock to the head. A brain bleed in the brain stem (if I'm remembering it right) will build up pressure until the stem suddenly disconnects. Not electrical, but such syndromes seem to be real.
    - dreamcompiler 7y ago
      It's quite real. This is why we try very hard (everything short of kidnapping) to take people to the hospital after a bad car wreck ("high energy mechanism of injury" is the term we use) even if they're walking around saying they're fine.
      - kube-system 7y ago
        Adrenaline is a heck of a thing. I know someone who similarly said they were fine and wanted to go home after being hit by a car. They had fractured vertebrae and their spinal cord would have likely suffered permanent damage if it wasn’t immobilized as soon as it was.
      - the-peter 7y ago
        The EMTs didn't try very hard when I was flipped by a drunk driver. I crawled out of my window and told the EMTs I just wanted to go home and they said 'ok'.
    - Cthulhu_ 7y ago
      Yup, definitely - this is why people will be asked if they blacked out, if only for a little while, after a fall. If they did the impact was severe enough to cause damage. And of course tight monitoring after head trauma.
    - tialaramex 7y ago
      Walking Ghost phase is a phenomenon in severe exposure to radiation. The patient survives initial ill effects (probably with advanced medical treatment) and now feels fine. They have no nausea, they can walk and talk like anybody else. If you tell them they're actually dying they likely won't believe you. Inside cell reproduction has stopped, and as enough cells naturally die without replacement over the next few days their systems will cease functioning and they'll die of multiple organ failure. Electricity definitely won't cause that, but yeah, humans can't sense all the terrible things that might have gone wrong with their bodies.
- dreamcompiler 7y ago
  You're right. When I was young and stupid I did wiring repairs on 110v circuits without bothering to switch them off. I got shocked a lot, but now that I'm older and smarter I know I just got lucky.
unlinked_dll 7y ago
I've gotten burned by changing light bulbs without turning off the switch; garnering me the nickname "Uncle Fester" by my family (in my defense - the light bulb was out and I wasn't thinking) and that shit definitely hurts. I've also been burned debugging a power supply for a GSM amplifier used in the test harnesses for a semiconductor fab (this time was carelessness, the power supply rails weren't taped off since I was probing it attempting to find a fault on the point-to-point wiring) that was powered at 240V and holy hell I do not recommend doing anything that stupid. If it doesn't have a safe way to repair, buy a new one.
- taneq 7y ago
  Burned or zapped? Light bulbs get thermally hot but glass is non-conductive. I haven't personally been bitten by 240V but from people I've talked to who have, I don't intend to chance it happening.
  - Qwertystop 7y ago
    I'd guess you could get zapped if you accidentally touch the metal part of the bulb (or the socket) while unscrewing the old one or screwing in the new one.
lb1lf 7y ago
-During the annual EE safety refresher course I take at work, the instructor makes a point of the fact that during domestic work, the electric shock is often merely the trigger for the real injury; you get zapped, then fall from the ladder you were on or whatever. (We have 240VAC mains, but I guess an unexpected jolt of 110VAC would be sufficient to make me jump...)
- jjeaff 7y ago
  110v or 240v will kill you dead where you stand. But it's not really about the voltage. The higher the voltage, the easier it is for the electricity to ground out through you. But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. Luckily, human skin is not highly conductive and neither are rubber soled shoes. So if you are taking proper precautions and not kneeling on a wet floor while using all metal tools on bare wires when someone flips a breaker back on, then your risk is rather minimal.
  - 6nf 7y ago
    > But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. 10-20 amps? Not across your skin! Usually a 220V zap at home won't cause instant death.
    - wlesieutre 7y ago
      That's the point made in the line after your quote > Luckily, human skin is not highly conductive and neither are rubber soled shoes. Could also note that depending on your circuit breakers, a short circuit will continue delivering higher than its 20A rated capacity for some time until the overcurrent protection goes off. Thermal breakers won't react as quickly to overcurrent as thermal magnetic breakers, so it depends on what kind of protective equipment is installed. EDIT: some reference on circuit breakers https://www.se.com/ww/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/242000/FA242032/en_US/CA908024E%20(web).pdf https://www.se.com/ww/resources/sites/SCHNEIDER_ELECTRIC/con... > For example: based on the curve on page 3, an iC60 circuit breaker of curve C, 20 A rating, will interrupt a current of 100 A (5 times the rated current In) in: 0.45 seconds at least, 6 seconds at most. 6 seconds is a pretty good chunk of time for a 20A circuit to happily be delivering 100A of current.
grawprog 7y ago
I dunno, I got electrocuted repeatedly a few weeks ago, not sure the voltage, I was using a wet saw and didn't realize the rubber had worn out on my boots and the steel plate in the soles was touching the floor. Every time I turned the saw on or touched it when it was running I got electrocuted. It was kind of funny, nobody could figure out why i was the only one being electrocuted. All my coworkers came and touched it and were fine. But, it wasn't the pain that got to me, it was the weird feeling in my body after. All the rest of that day I felt weird. My skin felt too sensitive, my arms would twitch randomly, and I just felt kind of weak and vaguely dizzy all day. I did end up figuring it out and putting a rubber mat down which immediately stopped the electrocution problem. But I really don't like being electrocuted at all. It just isn't pleasant. On topic, all our machines get locked and tagged before opening the electrical cabinets or working on anything where you might be exposed to live wires. It's enforced by worker's comp also. We get randomly inspected fairly regularly and one thing they check is that we have lockout keys and locks on every machine breaker.
- tomatotomato37 7y ago
  I find it interesting how you describe a job with a functional safety culture from the perspective of regulators, with lockouts and random inspections, that yet solves the issue of a power tool shocking workers at mains voltage by just tossing down a rubber mat and continuing to work with said malfunctioning tool.