4 ms·

Interesting. I’ve never tried it out, but I assumed that an RCD / GFCI would trip more or less instantaneously. I’m kind of surprised you felt much of anything.

TD-Linux 4y ago
They still mechanically open the circuit breaker, which takes time.
justsomehnguy 4y ago
> To reduce the risk of electrocution, RCDs should operate within 25–40 milliseconds Now divide 1000ms to 50Hz.
- NotYourLawyer 4y ago
  20 millisecond-seconds.
  - justsomehnguy 4y ago
    Or 16.6 for 60Hz networks. Do you remember what it's sine wave when you on AC? You will be applied to the current for up to 2-2.5 cycles, so it's up to amount of current what you will get. @londons_explore pretty summed it up and gave a link to a very good graph.
kube-system 4y ago
It is also important to note that ground fault devices only trip when there is a fault to ground. If your body becomes a conductor between live and neutral, you can draw up to the current limit for that branch circuit.
- sokoloff 4y ago
  For the timeframe relevant to your body, you can draw several multiples of the circuit limit for the branch circuit. (A breaker will typically pass around 3x its label rating for 3 seconds or more before tripping.) The resistance of your body would be the limit here rather than the breaker typically.
  - kube-system 4y ago
    Very true, not that 15a vs 45a would potentially be of any difference to the person being shocked. If anyone is low enough resistance to draw anywhere approaching either of those currents, they no longer care, as they are long dead.
londons_explore 4y ago
You'd be surprised... They usually can only trip at the end of the cycle - ie. in a 60 Hz power grid, that might take 17 milliseconds. Many take 40+ milliseconds. Luckily, electricity is about 20x safer as long as it is supplied for less time than one heartbeat[1] - ie. 500 milliseconds. Thats how RCD's can be so lifesaving even though they are relatively slow. [1]: https://en.wikipedia.org/wiki/Electrical_injury#/media/File:IEC_TS_60479-1_electric_shock_graph.svg https://en.wikipedia.org/wiki/Electrical_injury#/media/File:...
- londons_explore 4y ago
  Note that if you could design a faster breaker, more lives might actually be lost... Imagine you had an ideal switch that could disconnect a circuit instantly. Any devices powered on that circuit with transformers, inductors or motors in (think vacuum cleaners, power tools, microwaves, blenders, etc) will have a current flowing through them, and as that current is interrupted there will be a huge voltage spike - easily 10x the normal voltage for a few milliseconds. If a human is touching that circuit, the 10x higher voltage will cause 10x more current to flow into the human. Hooray - your 'safer' RCD kills more people. The real solution is to have a more complex switch which disconnects the circuit at the same time as shorting out the circuit, to allow any current that was flowing to gradually dissipate into the wiring resistance. To my knowledge, such things don't exist today.
  - MichaelCollins 4y ago
    Isn't the solution a GFCI outlet at the wall, not at the breaker? Suppose you're in a bathroom; near water with a hair dryer, space heater, or some other non-inductive load. If there is a short, the circuit is cut from that outlet; inductive loads in the rest of the house aren't involved.
    - londons_explore 4y ago
      Well there can still be an inductive load that you're disconnecting... Like the vacuum cleaner you idiotically used to try and clean a wet carpet... Luckily, the problem I described is almost a non-issue. Deaths due to electrocution in buildings with a GFCI have fallen to pretty much zero - there were only four deaths due to electrocution at home in the UK last year (where voltage is very high and RCD's are common). That figure includes deaths by suicide, lightning indoors, and deaths where an RCD wouldn't help such as poking around inside CRT's, so it's entirely possible an RCD is already saving every life.
angrygoat 4y ago
It's quite a few years ago now, but the thing I remember was pain in the moment, and then very sore muscles in my hand and arm, presumably because the muscles were convulsed by the shock. I was sore for a couple of days and then I was fine.

TD-Linux 4y ago

They still mechanically open the circuit breaker, which takes time.

justsomehnguy 4y ago

> To reduce the risk of electrocution, RCDs should operate within 25–40 milliseconds Now divide 1000ms to 50Hz.

NotYourLawyer 4y ago
20 millisecond-seconds.
- justsomehnguy 4y ago
  Or 16.6 for 60Hz networks. Do you remember what it's sine wave when you on AC? You will be applied to the current for up to 2-2.5 cycles, so it's up to amount of current what you will get. @londons_explore pretty summed it up and gave a link to a very good graph.

kube-system 4y ago

It is also important to note that ground fault devices only trip when there is a fault to ground. If your body becomes a conductor between live and neutral, you can draw up to the current limit for that branch circuit.

sokoloff 4y ago
For the timeframe relevant to your body, you can draw several multiples of the circuit limit for the branch circuit. (A breaker will typically pass around 3x its label rating for 3 seconds or more before tripping.) The resistance of your body would be the limit here rather than the breaker typically.
- kube-system 4y ago
  Very true, not that 15a vs 45a would potentially be of any difference to the person being shocked. If anyone is low enough resistance to draw anywhere approaching either of those currents, they no longer care, as they are long dead.

londons_explore 4y ago

You'd be surprised... They usually can only trip at the end of the cycle - ie. in a 60 Hz power grid, that might take 17 milliseconds. Many take 40+ milliseconds. Luckily, electricity is about 20x safer as long as it is supplied for less time than one heartbeat[1] - ie. 500 milliseconds. Thats how RCD's can be so lifesaving even though they are relatively slow. [1]: https://en.wikipedia.org/wiki/Electrical_injury#/media/File:IEC_TS_60479-1_electric_shock_graph.svg https://en.wikipedia.org/wiki/Electrical_injury#/media/File:...

londons_explore 4y ago
Note that if you could design a faster breaker, more lives might actually be lost... Imagine you had an ideal switch that could disconnect a circuit instantly. Any devices powered on that circuit with transformers, inductors or motors in (think vacuum cleaners, power tools, microwaves, blenders, etc) will have a current flowing through them, and as that current is interrupted there will be a huge voltage spike - easily 10x the normal voltage for a few milliseconds. If a human is touching that circuit, the 10x higher voltage will cause 10x more current to flow into the human. Hooray - your 'safer' RCD kills more people. The real solution is to have a more complex switch which disconnects the circuit at the same time as shorting out the circuit, to allow any current that was flowing to gradually dissipate into the wiring resistance. To my knowledge, such things don't exist today.
- MichaelCollins 4y ago
  Isn't the solution a GFCI outlet at the wall, not at the breaker? Suppose you're in a bathroom; near water with a hair dryer, space heater, or some other non-inductive load. If there is a short, the circuit is cut from that outlet; inductive loads in the rest of the house aren't involved.
  - londons_explore 4y ago
    Well there can still be an inductive load that you're disconnecting... Like the vacuum cleaner you idiotically used to try and clean a wet carpet... Luckily, the problem I described is almost a non-issue. Deaths due to electrocution in buildings with a GFCI have fallen to pretty much zero - there were only four deaths due to electrocution at home in the UK last year (where voltage is very high and RCD's are common). That figure includes deaths by suicide, lightning indoors, and deaths where an RCD wouldn't help such as poking around inside CRT's, so it's entirely possible an RCD is already saving every life.

angrygoat 4y ago

It's quite a few years ago now, but the thing I remember was pain in the moment, and then very sore muscles in my hand and arm, presumably because the muscles were convulsed by the shock. I was sore for a couple of days and then I was fine.