I'm not usually one to get hung up on this detail; maybe that's because I first learned "Murphy's Laws for Electricians."

These laws might read something like this:
1) If you test every wire but one, that one will be hot.
2) If you can grab any of several wires, you will grab the live one.
3) A $1000 TV set will sacrifice itself to protect a 5 cent fues.
4) Electricity is a malevolent thing, and will endlessly flow throug all the wiring, looking for a chance to zap you.
5) Expensive new wire cutters are better at finding live wires than old rusty ones.

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