10:52AM | 01/15/07
Member Since: 01/03/07
2 lifetime posts
I have a couple of wall outlets that are putting out around 40V instead of 110! Where could the resistance be coming from? I would think it would be pretty unusual to get a connection that was just bad enough to put up a lot of resistance, but not bad enough to shut the circuit down or to arc. What is goin on? I discovered it when I plugged in a cap-start motor (saw) and got nothing. Now I notice lights are dim when plugged there. This isn't used much so could have been that way for awhile. Help! Thanks!


03:09PM | 01/15/07
Member Since: 04/25/05
1916 lifetime posts
What you are measuring is phantom voltage. The circuit is open and you have a voltmeter with real high input impedence. What you see is capacitive coupling to other wires.

Most likely causes by bad connections from back stab connections on the receptacle. It could be in this receptacle or one that is up stream.


03:42PM | 01/15/07
Member Since: 01/03/07
2 lifetime posts
I'm surprised there's enough juice to make the 15A 110VAC saw motor hum and grind, but not quite turn. Is this dangerous, just for the record? I'm going to swap out the receptacles on that circuit and see if that works, anyway. Thanks!


05:14PM | 01/15/07
Member Since: 04/25/05
1916 lifetime posts
Early you had said "What is goin on? I discovered it when I plugged in a cap-start motor (saw) and got nothing."

But now you said that the saw hummed.

That is a big difference.

First I would verify that the saw it'self is still working by trying it at a good know recepactle.

Now IF you where making good contact with BOTH leads on a voltmeter AND there was NOTHING ELSE on the circuit a reading of 40 volts would have been phantom voltage and but the motor would not have even hummed and a light would not light.

One potentially confusing issues is that with a loose connection plugging and unpluging something in the receptacle can often change it from working or not working.

But the problem remains. Often getting worse and can cause a fire.

Tom O

03:38AM | 01/16/07
Member Since: 09/17/02
477 lifetime posts
Phantom voltages willl not light a light bulb, not even dimly as you stated in your original post. Plugging a table lamp (or other load) into a receptacle is the way that a possible phantom reading is eliminated. If it is a phantom reading, then it will dissapear under load.

If changing the receptacles doesn't work, you should consider calling an electrician. The connection that is causing the trouble could be located at a receptacle that is working OK or it could be in a junction box. Troubleshooting can be frustrating for the inexperienced (and the pros also).


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