7 ms·

I've been shocked by one of these – I was setting up some computers, asked for an extension cord, got handed a male-to-male cord. Didn't notice until I plugged

I've been shocked by one of these – I was setting up some computers, asked for an extension cord, got handed a male-to-male cord. Didn't notice until I plugged one end in, and grabbed the other while fishing around for it while looking. It never occurred to me that it might be male on both ends. The shock was very painful but the RCD tripped and saved my life. I'm quite grateful to the regulators here in Australia that made them mandatory back int he 90s.

NotYourLawyer 4y ago
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.
NoImmatureAdHom 4y ago
While a regrettable experience, it's extremely unlikely the RCD saved your life. Being shocked by 240V domestic supply is a thing that happens all the time, and deaths are very rare. Usually you'd have to have current passing through your heart, as if you grabbed a hot wire with one hand and were standing barefoot in a puddle with the opposite foot. Grabbing the end of a M-M extension cord like you described would probably result in current mostly flowing through your hand a little, then to the neutral or ground conductors.
puffoflogic 4y ago
Grateful to the same regulators that didn't outlaw suicide cables?
Nifty3929 4y ago
This is one nice thing about electric in the US - household voltage is mostly 110v, with special outlets for the occasional exception that requires 220v. And even in those cases, it's not 220v on one wire, it's just two wires of 110v. I've been shocked by 110v countless times (well, maybe a dozen or so), and it's just an momentary shock (in both senses) and nothing more. Not recommended! Be careful! Circumstances (water) can make it fatal! But still I've been fine. Australia and lots of other countries use ~240v as normal household voltage. I've never been shocked by 240v, but from your description I'm really glad about that. Are there any downsides for using 110v instead of 220v?
- MichaelCollins 4y ago
  110V AC can be enough to contract your muscles involuntarily, so if you get unlucky you may find yourself unable to let go. It's definitely safer, but still not safe. > Are there any downsides for using 110v instead of 220v? Not really, except that most appliances will only use 110v instead of 220v, because most power outlets are 110v with a few special 220v outlets set up specifically for heavier appliances. Usually 110v is perfectly adequate anyway, but electric kettles in America are slower.
- yetihehe 4y ago
  Depends on person. I've accidentally touched 220V several times and only felt a little stinging. One time I was kneeling on wet grass. But - please don't try it yourself, I'm just very lucky and probably a bad conductor, you might be not. > Are there any downsides for using 110v instead of 220v? You need thicker wires and higher current to carry the same power. In Europe electric kettles are much more common because they can use up to 2kW in most households without any problems.
- jakogut 4y ago
  > even in those cases, it's not 220v on one wire, it's just two wires of 110v. This is not really correct. Voltage is potential difference, so the voltage of a single conductor as measured from a single point is always zero, as there's no difference. Similar to how a boulder on top of a hill on Earth has potential energy from gravity, because there's a difference in height, and a force acting on that mass. That same boulder with no hill or gravity has no potential energy. In America, residential panels are generally wired with three current carrying conductors (hot, hot, neutral), and a ground. Each hot is one leg of a 240V transformer, and the neutral is a center tap, which has 120V of potential difference (voltage) between both hots. In 120V circuits, one hot is combined with the neutral for 120V of potential. Other circuits and outlets can combine two hots for 240V of potential, or two hots and a neutral for both 240V and 120V capability, such as might be used by your dryer, with large motors and heaters driven by the higher voltage, and control circuitry being powered by the lower voltage. > Are there any downsides for using 110v instead of 220v? Because the current required for the same amount of power at a lower voltage is higher (Ohm's law), thicker wire is required to carry that current, and more heat is generated. Source: DIYer who's wired my own garage, including a 100A subpanel and various circuits, which was all permitted and passed inspection.

NotYourLawyer 4y ago

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.

NoImmatureAdHom 4y ago

While a regrettable experience, it's extremely unlikely the RCD saved your life. Being shocked by 240V domestic supply is a thing that happens all the time, and deaths are very rare. Usually you'd have to have current passing through your heart, as if you grabbed a hot wire with one hand and were standing barefoot in a puddle with the opposite foot. Grabbing the end of a M-M extension cord like you described would probably result in current mostly flowing through your hand a little, then to the neutral or ground conductors.

puffoflogic 4y ago

Grateful to the same regulators that didn't outlaw suicide cables?

Nifty3929 4y ago

This is one nice thing about electric in the US - household voltage is mostly 110v, with special outlets for the occasional exception that requires 220v. And even in those cases, it's not 220v on one wire, it's just two wires of 110v. I've been shocked by 110v countless times (well, maybe a dozen or so), and it's just an momentary shock (in both senses) and nothing more. Not recommended! Be careful! Circumstances (water) can make it fatal! But still I've been fine. Australia and lots of other countries use ~240v as normal household voltage. I've never been shocked by 240v, but from your description I'm really glad about that. Are there any downsides for using 110v instead of 220v?

MichaelCollins 4y ago
110V AC can be enough to contract your muscles involuntarily, so if you get unlucky you may find yourself unable to let go. It's definitely safer, but still not safe. > Are there any downsides for using 110v instead of 220v? Not really, except that most appliances will only use 110v instead of 220v, because most power outlets are 110v with a few special 220v outlets set up specifically for heavier appliances. Usually 110v is perfectly adequate anyway, but electric kettles in America are slower.
yetihehe 4y ago
Depends on person. I've accidentally touched 220V several times and only felt a little stinging. One time I was kneeling on wet grass. But - please don't try it yourself, I'm just very lucky and probably a bad conductor, you might be not. > Are there any downsides for using 110v instead of 220v? You need thicker wires and higher current to carry the same power. In Europe electric kettles are much more common because they can use up to 2kW in most households without any problems.
jakogut 4y ago
> even in those cases, it's not 220v on one wire, it's just two wires of 110v. This is not really correct. Voltage is potential difference, so the voltage of a single conductor as measured from a single point is always zero, as there's no difference. Similar to how a boulder on top of a hill on Earth has potential energy from gravity, because there's a difference in height, and a force acting on that mass. That same boulder with no hill or gravity has no potential energy. In America, residential panels are generally wired with three current carrying conductors (hot, hot, neutral), and a ground. Each hot is one leg of a 240V transformer, and the neutral is a center tap, which has 120V of potential difference (voltage) between both hots. In 120V circuits, one hot is combined with the neutral for 120V of potential. Other circuits and outlets can combine two hots for 240V of potential, or two hots and a neutral for both 240V and 120V capability, such as might be used by your dryer, with large motors and heaters driven by the higher voltage, and control circuitry being powered by the lower voltage. > Are there any downsides for using 110v instead of 220v? Because the current required for the same amount of power at a lower voltage is higher (Ohm's law), thicker wire is required to carry that current, and more heat is generated. Source: DIYer who's wired my own garage, including a 100A subpanel and various circuits, which was all permitted and passed inspection.