I'm an electronics guy but my specialty is DC stuff, I know very little about AC wiring, so forgive my naivete...

I have an old 16mm slide projector I found in my grandparents house. The original AC cable was all frayed, so I opened it up and spliced in the new one, capping and taping everything and being very careful to make sure that there were no internal exposed wires that might contact the chassis. The only components inside are the projector bulb and an AC motor, and of course the switch.

There was no ground wire initially (and I replaced it with nonground two-conductor line). When I turn on the unit, I could touch it just fine (i know, i know, should always have had it grounded first), but when I double checked with my multimeter sticking one probe into either AC outlet side (hot or neutral) and touching the chassis or switch with the other probe, I'm getting a consistent voltage of about 20-40 AC and DC (don't have an oscilloscope to differentiate). Never felt a shock, and haven't tried checking the amperage yet (as I don't know how to check it in series...unless I do the same way?) Anyhow, wondering if anyone can comment on what this spurious voltage is, why it didn't shock and kill me, and how to make this thing absolutely safe...

Thanks all!

  • 20-40v is difficult to feel with dry hands, and it could have no current, which means that any conductor better than your DMM's 10M ohm series resistance drops the voltage. that said, metal chassis should be grounded.
    – dandavis
    Dec 15, 2017 at 12:04
  • It could be a little phantom voltage being generated by the wiring inside the case, a low impedance volt meter probably would not detect it. Phantom voltages have very little potential think of a transformer with only 1 wrap of wire you would see voltage but not much current. With all that said today's standards are to ground conductive cases.
    – Ed Beal
    Dec 15, 2017 at 17:54

1 Answer 1


If the projector has a metal case then it should be grounded. Buy a new three wire appliance cord and secure the green wire to the case. Make sure it is always plugged into a grounded receptacle. Then you can test the current draw on the ground wire. (use a clamp type meter) This will tell you if you really have a problem. The tests you site mean little or nothing.

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