How check power connection?

[Dansing]

Last week I had to re-wire my table saw because the shop I am now in has different 220V/20A outlets. The table saw is a Powermatic 66 220V single-phase 3HP. About an hour after I did this, I was checking the run-out, pressed my knee against the power switch box, and got a sharp shock! Fortunately, only my right side was leaning against the saw at the time; my left hand and leg were not touching it, so the shock did not pass through my heart. It did wake me up a bit.

Today I pulled the wiring out and found a couple of places where the wires had gotten nicked, so I re-wired it. I protected the power cable where it goes into the power switch box with electrical tape as it appeared that was where it had shorted out.

My question is this. How do I verify/check my connections without getting shocked again? How does an electrician do this?

Bob

[Juergen Hannappel]

[...]

The proper way is to use an isolation measurement device, which puts the wires on a rather high tension (500 od 1000V) and then with a special probe all the surfaces are checked. Another point to check is the conductivity of the wires, where the right way is to measure with short high current pulses, again with a special device. Anyway it seems that the protective earth of your saw was not connected properly, otherwise the fuse would have blown, saving you from shock. Maybe also the wall receptacle has no proper protective earth connection.

[Jim]

Interesting... Did you make certain that the ground wire (it is either the bare one or the green one) is connected to the box which is then bolted to the saw? Your experience indicates not. There should be no need for tape inside a box; in fact, if the tape helps, you have not connected everything correctly. By the way, does your switch disconnect both hot wires? That 220v motor won't appreciate getting 110v from one leg of the wiring. Jim

[Battleax]

You should not need electrical tape, you should have the correct fittings and wire for the box.

Electricians do it by knowing exactly what they are doing.

[LRod]

That 240V motor won't care any more about one side of the circuit being disconnected than a light bulb does in a lamp with a non polarized plug that has the neutral side of the plug in the hot socket (normal and legal for many, many years).

[no(SPAM)vasys]

With an ohmmeter and the saw unplugged.