Author Topic: Got shocked by 120VAC  (Read 3312 times)

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Offline james_s

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Re: Got shocked by 120VAC
« Reply #50 on: June 14, 2021, 05:07:19 am »
American GFCIs are typically only used for branch circuits that are in damp locations, originally they were only required for outdoor and bathroom receptacles, now they are required in kitchens, garages and some basements too. In the UK the ones I saw were the main breaker in the entire panel, maybe they figure 5mA would make it too much of a nuisance.
 

Offline Siwastaja

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Re: Got shocked by 120VAC
« Reply #51 on: June 14, 2021, 07:11:57 am »
30mA has the advantage that you can use a single unit to protect several groups of circuits.

It's a tradeoff, RCDs/GFCIs were much more expensive in the past, and it's better to have a very good albeit not perfect protection than no protection at all. You can of course force new installations to use however expensive solutions, but voluntary retrofits really benefit from the fact you can just install one unit in one place.

And I guess a 30mA RCD protecting the whole house is better safety-wise than 6mA units protecting only the bathrooms.
 

Offline Zero999

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Re: Got shocked by 120VAC
« Reply #52 on: June 14, 2021, 12:35:55 pm »
Another benifit of an RCD for the whole house is, it provides protection for cables inside the walls, in case somone hammers a nail through a cable, in the wall, when they're hanging a picture.
 

Offline dunkemhigh

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Re: Got shocked by 120VAC
« Reply #53 on: June 14, 2021, 01:21:14 pm »
Quote
in case somone hammers a nail through a cable, in the wall

When installing network cable at a previous employer, I drilled through a wall to find the bit had gone clean through the middle of T&E, leaving scuffs but unbroken insulation on live & neutral and somehow missing earth completely.

Mind, that wasn't nearly so annoying as feeding coax between floors down the shaft behind toilet cubicles, only to find the seat left up on the lower level so the cable had come out of the wall and continued its merry way down the u-bend.
 

Offline james_s

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Re: Got shocked by 120VAC
« Reply #54 on: June 17, 2021, 06:37:04 am »
Another benifit of an RCD for the whole house is, it provides protection for cables inside the walls, in case somone hammers a nail through a cable, in the wall, when they're hanging a picture.

We're not allowed to run wires such at this can reasonably happen to them. Code requires a metal nail plate be installed over every stud where a wire passes through it.

https://www.homedepot.com/p/MiTek-1-1-2-in-x-3-in-G90-16-Gauge-Protection-Plate-60-Pack-UKNS1BK/313491991
 

Offline Zero999

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Re: Got shocked by 120VAC
« Reply #55 on: June 17, 2021, 02:26:24 pm »
Another benifit of an RCD for the whole house is, it provides protection for cables inside the walls, in case somone hammers a nail through a cable, in the wall, when they're hanging a picture.

We're not allowed to run wires such at this can reasonably happen to them. Code requires a metal nail plate be installed over every stud where a wire passes through it.

https://www.homedepot.com/p/MiTek-1-1-2-in-x-3-in-G90-16-Gauge-Protection-Plate-60-Pack-UKNS1BK/313491991
The same is true here, but there's always the outside chance someone will do something stupid, hence the requirement for an RCD.https://the-regs.co.uk/blog/?p=586
 

Offline Siwastaja

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Re: Got shocked by 120VAC
« Reply #56 on: June 17, 2021, 05:12:29 pm »
Obviously an RCD has no purpose if everything is done properly by the rules and maintained as such.

It's exactly there to save lives in cases of human error, including wiring in the wrong place.
 

Online ejeffrey

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Re: Got shocked by 120VAC
« Reply #57 on: June 17, 2021, 06:00:43 pm »
For the unbelievers, here's a 9V battery death:

https://darwinawards.com/darwin/darwin1999-50.html :popcorn:

I am an unbeliever, I think that story is almost certainly a myth or widely distorted.

There is an easy and completely safe demo of this.
 Go take a multimeter and a jar of saline solution at human body temperature and measure the resistance just dunking the probe tips in.  You will find it is quite high.  The reason for that is the probe tips are have low surface area and the spreading resistance around them is still quite high.  Now if you attach some alligator clips and some copper braid and try again there will be a much lower resistance.  At low voltages it is a much bigger problem if you grab onto a large metal pipe vs pierce the skin with a small probe.
 

Offline dunkemhigh

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Re: Got shocked by 120VAC
« Reply #58 on: June 17, 2021, 08:00:42 pm »
Head to foot resistance of the body appears to be ~400R which would give 22mA from a 9V battery. Since it's not head to foot, a larger current and severed complications seems possible. Possibly mitigated by being DC, though.

https://www.researchgate.net/publication/335250921_Electric_Shock_Drowning_Causes_and_Prevention
 

Online ejeffrey

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Re: Got shocked by 120VAC
« Reply #59 on: June 17, 2021, 09:13:26 pm »
Head to foot resistance of the body appears to be ~400R which would give 22mA from a 9V battery. Since it's not head to foot, a larger current and severed complications seems possible. Possibly mitigated by being DC, though.

https://www.researchgate.net/publication/335250921_Electric_Shock_Drowning_Causes_and_Prevention

Go do the experiment I suggested.  Getting hundreds of ohms through salt water requires a very large electrode area. 
 

Offline dunkemhigh

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Re: Got shocked by 120VAC
« Reply #60 on: June 17, 2021, 11:33:33 pm »
Probes pushed hard enough to pierce skin would, I think, be a different scenario to tips dipped into saline solution gently enough not to disrupt surface tension. Thus I have a better idea: you repeat the sailor's experiment and then come back to tell us it is rubbish.

[Edit: typo]
« Last Edit: June 18, 2021, 07:51:00 am by dunkemhigh »
 

Offline Deimos

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Re: Got shocked by 120VAC
« Reply #61 on: June 18, 2021, 07:12:09 am »
My first 120v shock was when I was a teen 20 years ago fiddling with a Technics 5 disc CD changer, I was testing some stuff and forgot I had it plugged in when I rested my arm on the 120v input.

My worst shock however, was from a CRT television I was trying to see why it didn't work, again young teen and knew next to nothing, but had to start somewhere right?  :palm: Anyway grabbed the flyback anode cap at the CRT and it zapped my entire right arm, horrible pain through my entire arm that lasted for several minutes (I didn't even know what that suction cup thingy was  :P). The TV was unplugged mind you, but I didn't know the CRT held a charge. Live and learn I guess and still be a alive.  :scared:

Learned not to be so careless after that. I did a lot of reading / research on discharging CRT's, capacitors, high voltage, etc. and none of that happened again.  That was a nasty shock though.
 

Offline Siwastaja

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Re: Got shocked by 120VAC
« Reply #62 on: June 18, 2021, 12:18:20 pm »
I have hard time believing that 9V battery story as well.

And I'm not saying the incident itself didn't happen; no, I can believe that it happened, but I have hard time believing the analysis of 9VDC being so dangerous after you remove the skin from the equation.

People just die. Recently there was this soccer incident all over the media, 0 volts was involved; people have hidden heart conditions and they may trigger due to physical stress, doing sports, having sex, piercing your skin with multimeter probes while applying 9V DC; or, for no apparent reason whatsoever!
 

Offline G7PSK

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Re: Got shocked by 120VAC
« Reply #63 on: June 18, 2021, 02:15:40 pm »
Surely it is neither the volts or amps that kill but the power, somewhere arround 35j/s would appear to be what is required.
 


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