Electrical shock??
Electrical shock??
(OP)
Good day people.
My first post here.
I was looking for a general electrics thread but couldnt find anything, so I hope you guys dont mind helping.
What I would like to know is the following:
If I accidentally touch a live wire and am not insulated from ground, what would the current flowing through me be, and would it make a difference if there is current flowing through the wire at the time (eg if the motor is off at the time or is drawing say 10A)? Would that affect the severity of the shock?
And secondly, why is it that 3-phase power is more dangerous than single?
3-phase line voltage is much higher yes, so I understand that if I touch two 3-phase live wires I will get a much worse shock, but even with 3-phase the live-ground voltage is exactly the same as single phase (220V in my country). Would I get a worse shock? And if yes, why?
Thanks for any replies.
My first post here.
I was looking for a general electrics thread but couldnt find anything, so I hope you guys dont mind helping.
What I would like to know is the following:
If I accidentally touch a live wire and am not insulated from ground, what would the current flowing through me be, and would it make a difference if there is current flowing through the wire at the time (eg if the motor is off at the time or is drawing say 10A)? Would that affect the severity of the shock?
And secondly, why is it that 3-phase power is more dangerous than single?
3-phase line voltage is much higher yes, so I understand that if I touch two 3-phase live wires I will get a much worse shock, but even with 3-phase the live-ground voltage is exactly the same as single phase (220V in my country). Would I get a worse shock? And if yes, why?
Thanks for any replies.





RE: Electrical shock??
It's impossible to predict, because of the number and nature of impedances in the circuit you form. Usually the soles of your shoes protect you, but not always.
>>>... and would it make a difference if there is current flowing through the wire at the time ...<<<
No.
Mike Halloran
Pembroke Pines, FL, USA
RE: Electrical shock??
3-phase line voltage is much higher yes, so I understand that if I touch two 3-phase live wires I will get a much worse shock, but even with 3-phase the live-ground voltage is exactly the same as single phase (220V in my country). Would I get a worse shock? And if yes, why?<<<
Line-ground 220V is Line-ground 220V. Shock is no worse. Three phase same as single phase.
Do not try to measure this.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Electrical shock??
As for severity it's all about the insulation involved and the specific path through the body that the current travels through. Dry human skin has a resistance of about 10,000ohms. So at a minimum you're probably talking about 20,000ohms. With 120Vac as the source the peak current could be as little as Vpeak = √2 x 120 or 170V/20,000 = 0.0085Amps
Since 0.005A across the heart is the generally accepted level to cause death you can see where you are. It's tenuous. Add shoes and you're probably way below 5mA. Run the current between hands and you're back to seriously dangerous. Add water.. Add sweat. Raise the voltage..
A favorite peeve of mine is hearing people say, "Every time I touch the 'fill in device' I get a shock". These people are fools. Why? because all they need to do is change up one aspect like wet carpet, or wet shoes, or no shoes, a wet hand, or more pressure somewhere, and they easily pile on several more milliamps and a shock transitions to an electrocution.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Electrical shock??
RE: Electrical shock??
To elaborate a little on the "if there is current flowing through the wire at the time (eg if the motor is off at the time or is drawing say 10A)?"
As was said if there is current flowing, the wire is live so it would not make a difference what else was connected and you can be killed. If a motor is "off" and you grab the motor lead, DOWN STREAM of whatever is rendering it "off", then there would likely be no voltage, so no shock. But that is a horrible idea to test unless you can ENSURE that whatever is keeping that circuit open will REMAIN open. Here in North America, we call that "Lock-Out/Tag-Out" because you open a disconnect switch, test that it is really open, then place YOUR own lock on the handle so that the disconnect cannot be closed while you are working on the circuit, and a tag on the lock with the date and time telling anyone that you are working there (in case they feel inclined to cut your lock off).
One related aspect of 3 phase that MIGHT make it seem more dangerous is that if you have a 3 phase motor running, and you open only 2 of the 3 phases, the motor will stop and someone may BELIEVE that the circuit is safe. But that 3rd phase will still be live and lethal.
"Will work for (the memory of) salami"
RE: Electrical shock??
I think the reason why there is a stigma around the danger of 3-phase is simply because most accidents and deaths happen in industrial applications and 3-phase is the norm in industrial applications.
Also in factories there are much more wires lying around wanting to be touched by an uninformed person, where in say, housing, where single phase is the norm, lots more effort is done to take all wires out of site.
RE: Electrical shock??
The 5 mA 'rule of thumb'. Is it peak, or is it RMS? The average heart rate is about 80 beats per minute. Would that 1.414 really make a difference?
I suspect that getting approval for a double blind medical experiment may be a tad problematic.
As an aside, my worst ever encounter was placing my forearms across 415V P-P busbars many moons ago. Completely my fault. I was hungover; I'd "isolated" the machine, and forgot it was dual fed. Threw me back and only a nice sturdy concrete wall stopped me going back even further. I was lucky, I was about 30 and as fit as a mallee bull at the time. That was well over twenty years ago now, and I suspect the outcome may be slightly different if I tried it again.
RE: Electrical shock??
I know this doesn't apply to anyone in the thread, but I have to mention anyway - It gets me worried when we talk about sharpening pencils to factor of 2 or doing measurement of our body resistance as if to say we may reach a conclusion about what is dangerous through these calculations. Follow standard safety procedures, not homemade calculations.
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(2B)+(2B)' ?
RE: Electrical shock??
If a shock is the result of an incident where the skin is punctured, BEWARE.
Bill
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"Why not the best?"
Jimmy Carter
RE: Electrical shock??
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Electrical shock??
jraef, how did you get phase to phase voltage on a delta system if you were the only fault?
Also on higher voltages you don't need to be connected physically to ground to become electricuted. The capactance of your body to ground will conduct enough current to electricute a person (notice birds are much smaller than us, before anyone asks).
RE: Electrical shock??
So for example while inadvertantly shorting across 120volt might typically cause some sparks (*), shorting across 480volt might cause a flash or blast.
(*I'm not saying it's safe to short across 120volt either).
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(2B)+(2B)' ?
RE: Electrical shock??
RE: Electrical shock??
RE: Electrical shock??
In fact I haven't seen very many large loads, just gobs of smaller load located in one place. Server farms, lights, pumps, and a few chillers. No large compressors, pumps, etc.
RE: Electrical shock??
I once got 600 Volts phase to phase between my thumb and finger. (LOTO error due to a faulty meter.) It burned a small hole in my thumb and a matching hole in my finger. My choice of words WAS NOT politically correct.
Bill
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"Why not the best?"
Jimmy Carter
RE: Electrical shock??
Although I am taking about a 7 kV delta system, it can still apply to 480 V, but to a lesser extent.
Politically correct? I would have said something R rated or something about our creater, but nothing political.
RE: Electrical shock??
*Side note: Would that be the potential potential? Then if so, wouldn't it be the potential2? Then if so, would that make it 230.4kV? Inquiring minds want to know!
"Will work for (the memory of) salami"
RE: Electrical shock??
In other countries they use delta secondaries, but they don't look for ground faults. So if you have a ground in a light for example, you may only get a shock in the shower if that light is on. Or it could be a ground in the house next door. They clame the delta system is safer, but with the reduced insulation they use it may not be so.
jraef, don't worry I can't read the voltage by toughing the wire either.