Electrical shock from the AC neutral wire?

Is it possible to be shocked by touching the neutral line of a 3 wire 120 VAC system (Line, neutral, ground). Assuming all circuits are working, I can only imagine a large voltage drop on the neutral line of maybe 50 volts that would cause a shock. But that's a lot of current in the neutral line to develop 50 volts.

-Bill

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Reply to
Bill Bowden
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Or a faulty eart connection with some current flowing

Reply to
David Eather

Normally? No.

For a while at a place I worked there were two different circuits, sourced from different ends of the building, that had about 40V difference between the grounds.

My takeaway lesson from that is to not trust nuthin'.

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www.wescottdesign.com
Reply to
tim

Normally no, you say it. But there is always one more bug.

w.

Reply to
Helmut Wabnig

Yep. While setting up a coaxial data link between two OmniComp/GenRad buildings in Phoenix (~1985), I found 60VAC between grounds :-( ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Yes, looks like making a good ground connection is more complicated than just pounding a stake in the ground. Here's an interesting wiki page that recommends installing a conductor that encircles the entire building below the foundation. The math is fairly complicated.

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Reply to
Bill Bowden

If everything is wired correctly to code and there are no defects, the neutral (white) wire in branch circuits (and the neutral bus in the panel) will not rise high enough above ground to shock you. Under normal conditions it should be well under 5 volts above ground.

However, even with all circuits working there can be defects.

You can be shocked by the neutral (white) wire if there is a defect in the wiring. I'll show two examples. The first is a wiring error with a switch wired in the white wire to an outlet (using a bulb in the example, but it could be a switched receptacle):

panel hot(black)---------bulb---white(neutral)---+ | panel neutral(white)------------------[Switch]---+

The white wire in the junction box with the bulb is at

120 V when the switch is open. The white color identifies the wire as the neutral leg, but the incorrectly wired switch interrupts the connection back to the panel. The circuit works just fine, but exposes you to danger.

Another example concerns a shared neutral circuit (also called a multiwire branch circuit) like this:

Phase1 hot(black)--------+ | [Load1] | Neutral(white)-----------+

Reply to
ehsjr

Yes, the switch needs to be on the hot side, not the neutral. Not familiar with multiphase setups but I get the idea. I experimented this morning with two blank copper clad circuit.boards on a table with a ohm meter connected between the boards. I wet my hands and placed one hand on each board and pressed down and got my body resistance to drop to about 5K ohms. I was reading somewhere that a mild shock is only about 1 milliamp, so it looks like you could get a mild shock from just 5 volts under perfect conditions. But an osha reference indicated wet body resistance could go as low as 200 ohms. Not sure I believe that. Maybe that's with an open wound where the skin is broken. I hear they take great care during open heart surgery to keep the stray voltages close to zero.

-Bill

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Reply to
Bill Bowden

Yes, the switch needs to be on the hot side, not the neutral. Not familiar with multiphase setups but I get the idea. I experimented this morning with two blank copper clad circuit.boards on a table with a ohm meter connected between the boards. I wet my hands and placed one hand on each board and pressed down and got my body resistance to drop to about 5K ohms. I was reading somewhere that a mild shock is only about 1 milliamp, so it looks like you could get a mild shock from just 5 volts under perfect conditions. But an osha reference indicated wet body resistance could go as low as 200 ohms. Not sure I believe that. Maybe that's with an open wound where the skin is broken. I hear they take great care during open heart surgery to keep the stray voltages close to zero.

-Bill

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Reply to
Bill Bowden

I once did a similar experiment but with a 4.5V supply and lengths of metal tubing, and can say that you surmise correctly. such a low voltage can give you a surprise in ideal circumstances.

Some of that resistance is actually a fixed voltage drop, 9V powered and 1.5V powered ohm meters will give different readings, and yeah broken skin makes a difference.

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umop apisdn 


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Reply to
Jasen Betts

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