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TJF 11-01-2011 01:39 PM

Odd voltages at outlet
 
I have an outlet (B) that receives its power from another outlet (A). Outlet A, in turn, receives its power from the breaker box.

I replaced Outlet A yesterday because the blade receivers on one of the sockets had burned over the years. I shut off the breaker and checked voltages at each wire connected to the outlet, and all read zero. Then I disconnected the four wires from outlet A. Two wires, brown and white, came from the breaker box, and two other wires, black and white, went behind the wall to outlet B.

Then I closed the breaker again, just to make sure there was actually power at Outlet A. The wires from the breaker read 117 volts from the brown to the white or from the brown to the metal of Outlet A's box. The wires from Outlet B read zero volts between black and white and between either black or white and Outlet A's metal box.

However, when measuring from the brown of Outlet A to the black of Outlet B, I got 62 volts and from the brown of Outlet A to the white of Outlet B I got 54 volts. This was with Outlet B pulled out of its plastic box, and touching nothing. Also the wires that had been connected to Outlet A were "floating" in the air, not connected to anything.

I should add that Outlet B had the bare wire connected to the grounding screw of the outlet. The other end of the bare wire connected to the grounding screw of the metal box of outlet A. The bare wire from the breaker was also connected to the grounding screw of Outlet A's box. However, Outlet A's grounding screw wasn't connected to anything when I took the voltage measurements.

Anyone have any idea what's going on with the 62 and 54 volt readings?

AllanJ 11-01-2011 02:09 PM

You are most likely reading phantom or induced voltage in dead wires, caused by wires such as in Romex cables running juxtaposed over long distances. Very sensitive voltmeters including most digital voltmeters will read phantom voltage.

Connect an incandescent light bulb of at least 15 watts across the two meter probes. If it glows even dimly and the voltage stays at the 54 or so volts you measured then you have a real problem somwhere (it's not phantom voltage) whereas if the voltmeter drops to zero then all is well and you are reading phantom voltage.

a7ecorsair 11-01-2011 02:43 PM

You are not following a logical troubleshooting procedure. You said you had 117 at the breaker and receptacle A.
Before leaving A measure the voltage from the black to white on the second set of terminals. If it reads 117 go to receptacle B and measure the voltage on the black and white wires that come from A. If it doesn't read 117 then the wires you think go from A to B, may not!

TJF 11-01-2011 05:53 PM

Thanks for the replies!

a7ecorsair: I am sure the wires connected to Outlet B get their power from Outlet A. There are two reasons I know that. When I decided to replace Outlet A, I grabbed an old outlet that I had in my "junkbox" in the basement, and after wiring it in to replace the original was very pleased with myself until my wife told me that Outlet B wasn't working any more. Then I realized the replacement Outlet A had the jumper across the hotwire (brass screw) terminals had been opened by the original installer, so I had to go to the local hardware and buy a new duplex outlet, and after installing, Outlet B has power again.

I don't know why the jumper had been opened, and am hoping it didn't have something to making Outlet B a switched outlet.

The other reason I know B is connected to A is that I can pull the wire connected to A and feel the tug on the white and black (and bare) wires entering the metal box where A is installed.

AllanJ: The voltmeter I used was indeed a digital one, and the wires are romex, but the romex from the breaker comes down from the attic into the top of the metal box that contains Outlet A whereas the wires to Outlet B go out the bottom of the metal box and continue down to Outlet B which is near the floor of the living room which is on the other side of the wall from the kitchen. Outlet A is in the kitchen and is above a kitchen countertop. Just the same, I'll try the test for a phantom voltage.

Something interesting to me is the sum of those two voltages I found and mentioned in my original post: the voltages are 62 volts and 54 volts, and that adds up to 116 volts, which is pretty close to the 117 volts I'd expect from the hot wire to the neutral or ground. Hmm.

a7ecorsair 11-01-2011 06:32 PM

Quote:

Originally Posted by TJF (Post 761690)

Something interesting to me is the sum of those two voltages I found and mentioned in my original post: the voltages are 62 volts and 54 volts, and that adds up to 116 volts, which is pretty close to the 117 volts I'd expect from the hot wire to the neutral or ground. Hmm.

You are not "adding" voltages. Remember, the neutral was properly carried through to receptacle B. By connecting your meter as you did, you placed it in-series with any connected load at B or past B.
As far as troubleshooting, had you taken the readings on both sets of lugs on receptacle A you would have found the problem immediately.

TJF 11-01-2011 07:01 PM

a7ecorsair, thanks for the new comment.

I am probably just being dense here.

When I measured those voltages, all wires were disconnected from Outlet A, and were "hanging in the air". The wires from the breaker box were disconnected from A, and the wires to Outlet B were disconnected. In fact, Outlet A was out of its box and lying on the countertop.

Outlet B was pulled out of its plastic box, and there was (as far as I could see) no load on the outlet: that is, nothing was plugged into the outlet.

Why would a meter connected from either wire (black or white) that leads to Outlet B show a voltage difference between the hot breaker wire? Could I have a fault in Outlet B that makes a resistive connection between those wires to the ground wire that is connected to Outlet B?

It just now occurred to me that I haven't tried disconnecting the black and white wires on the Outlet B end of the romex.

I also hadn't considered, before this moment, whether the metal clamp that holds the romex leading out of the metal box of Outlet A to the plastic box of Outlet B has squashed the insulation of the black and white wires and making a resistive path to ground there.

Like I say: dense!

a7ecorsair 11-01-2011 07:09 PM

So that breaker only supports those two receptacle and nothing else? No other receptacles or lights are on that circuit? That's a little odd....

TJF 11-01-2011 08:45 PM

No, the breaker controls two other outlets in the kitchen: one on both sides of the kitchen sink, and one of those is an old ground fault interrupter.

TJF 11-01-2011 08:53 PM

Ooh. Now I wonder if the circuit is from the breaker to the GFI to the other outlets. I'll have to check that by plugging a load into Outlets A and B and pushing the "test" button on the GFI.

TJF 11-01-2011 09:19 PM

I did some checking and found that the GFI controls its own duplex outlet as well as three undercabinet flourescent lamp fixtures above the sink and the countertops on either side of the sink.

The GFI does not control the duplex outlet on the other side of the sink, nor does it control Outlets A and B.

Also, when I tripped the breaker I've been talking about, the flourescent lights go out and a lamp plugged into Outlet A or B goes out. However a lamp plugged into the "other" sink-side outlet stays lit.

So I think this means that the breaker is connected in parallel to the GFI (which protect the flourescent lights) and to Outlets A and B.

a7ecorsair 11-01-2011 09:27 PM

Quote:

Originally Posted by TJF (Post 761853)
So I think this means that the breaker is connected in parallel to the GFI (which protect the flourescent lights) and to Outlets A and B.

The breaker is in series with all the parallel connected receptacles and lights.

TJF 11-01-2011 10:11 PM

Oops. I wrote "So I think this means that the breaker is connected in parallel to the GFI (which protect the flourescent lights) and to Outlets A and B."

but I meant "the GFI and Outlets A and B are connected in parallel with each other, with one wire going from the "top" of the parallel connection to the breaker. I guess that means they are in series with the breaker but in parallel with each other.

I'm like the absent-minded professor who went to the blackboard and said "a", wrote "b", but meant "c".

TJF 11-01-2011 10:13 PM

I just remembered the name for the connection: series-parallel.


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