Why choose 120 volts?

Tue May 26 22:43:36 UTC 2009

Barney Wolff wrote:

> Getting back to reality, I've watched more than one electrician do a
> two-finger liveness test on a 120v circuit, and done it myself.  240v
> HURTS, and I've not seen a pro finger it deliberately.  But I haven't
> actually asked.

During my residential electrical apprenticeship, one of the tricks of
the trade I learnt was a quick two finger test on 120, but never
anything higher than that.

That was years ago. I would never do anything of the sort intentionally
ever again, even on low voltage systems (my girlfriend is an
Occupational Health and Safety Officer, and she frowns on that sort of
thing ;)

It really depends on your conductivity to ground ie what you are
standing on and the shoes you are wearing whether you will remain safe
by 'testing' for hotness on a circuit by touching it.

@120V, 1.2 mA is enough to tell you that the line is live. 15mA is the
let-go threshold, and 100mA can kill within a second. 200mA will pretty
much kill instantly.

Even at 120V on non-conductive ground, if you ever accidentally touched
the grounded box while touching the live wire, you will likely be dead
before the breaker trips.

Steve
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