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DanBress 08-10-2008 03:15 PM

middle of the run box broken
 
I am fixing up a room in my house and decided to replace the outlets in the room, and the lighting fixture.

I am having an issue with one outlet, that appears to be a middle of the run outlet, with two sets of wires coming into the junction box.

I am an idiot, and didn't take note of how things were originally connected.

I hooked things black/black on my brass screws and white/white on my silver screws. When I flipped the breaker back on, it immediately broke.

I turned it off, disconnected the outlet with two sets of wires coming in, turned the power back on and measured the voltages across the different wires and this is what i found.

I have 4 wires
1White, 1Black
2White, 2Black

1W -> 2W = 0 volts
1W -> 1B = 120 volts
1W -> 2B = 0 volts

2W -> 1B=120 volts
2W -> 2B = 0 volts

1B -> 2B = 120 volts

Any ideas how to trouble shoot this?

It looks like wire 1 is my supply side, and wire 2 is my send to the rest of the load side. Any idea why wire 1 black to wire 2 black is showing 120 volts? Everything worked fine before i swapped outlets.

thanks,
dan

theatretch85 08-10-2008 03:56 PM

My first thought was that the original outlet was half switched, but that wouldn't make sense to have 120 volts across 2 black wires. If it was being fed power from two separate circuits, the 2 black wires should show 240volts in that case, not the 120. So my next guess would be that somewhere down the line, that 2B wire is being shorted to ground or is reverse wired somehow and is acting as a ground/neutral wire in this circuit.

DanBress 08-10-2008 04:04 PM

Quote:

Originally Posted by theatretch85 (Post 147552)
My first thought was that the original outlet was half switched, but that wouldn't make sense to have 120 volts across 2 black wires. If it was being fed power from two separate circuits, the 2 black wires should show 240volts in that case, not the 120. So my next guess would be that somewhere down the line, that 2B wire is being shorted to ground or is reverse wired somehow and is acting as a ground/neutral wire in this circuit.

Well it's definitely not half switched, because the outlet in question only had one outlet(not two).

hmmm. how would you recommend figuring out where the short is? Visually? Should i connect the middle outlet in question, and do voltage tests along the line?

theatretch85 08-10-2008 04:08 PM

Did this original outlet look like a standard duplex outlet? That is, could you plug in a standard appliance to it, or were the prongs of the outlet positioned differently? I would check to see what outlets do not have power with those 4 wires disconnected, if its in the middle of a run there will be something downstream that doesn't have power. Start by opening those boxes and visually looking for shorts; the bare ground wire is usually the culprit in cases like this.

DanBress 08-10-2008 04:36 PM

this was an old two prong outlet(no ground), it was a standard two prong. but there was only one outlet in the gang box.

all the wiring is the old metallic shield it looks like this, but is only 2 wires, not three.

http://z.about.com/d/homerenovations...-/bxwiring.JPG

I've had an issue in the past where the cloth wiring has deteriorated and part of a wire is touching the gang box, and grounding it's self. I guess i'll keep my eyes peeled for this situation.

DanBress 08-13-2008 06:26 PM

I did some more investigating to try and figure out what is going on here.

I believe the following to be true:

there are two pairs of wires in this junction box

one comes is the supply side which comes from my service panel,
and the other feeds a light switch above the outlet(note, the switch doesn't control the outlet, it controls an overhead light). from here the circuit branches to a switch on the other side of the wall, which controls a light for that room, and branches down towards another outlet.

I disconnected the first switch directly above the outlet, and separated the black wire, so in theory there is a black wire that goes from the junction box up to the switch junction box and ends right there. The white wire in theory goes up from the junction box and into the switch panel where it is soldered to all the other white wires.

I measured the voltage from black to black in the junction box where I am having problems and now I get 78 volts instead of 110v.

Can anyone offer any other tips to trouble shoot this issue?

Dan

Wildie 08-13-2008 09:02 PM

Using a white wire as a reference can sometimes be a problem.
In the past, to have a reliable reference ground, I have run an extension cord from an outlet that is functioning properly!
First check the neutral and hot on the extension cord and make sure that these are correct.
( from slot to slot - 120 volts)
( from ground to small slot -120 volts)
( from ground to large slot - zero ohms)
Once the neutral has been positively identified, connect the voltmeter from the large slot in the extension cord, to the wire to be tested. [on a voltage scale]
When you have determined what seems to be the feeder cable and that no potential is found on the feeder white wire, switch to ohms and verify that it is of ground potential.
Then verify that the box, itself is grounded. If it is fed by a metallic sheathed cable, it should be, but it may not be as old cables can become ungrounded over the course of time. This why cables today are required to have a third grounding wire.
In my own home, it had some old metallic sheathed cable with rubber covered conductors. I found that the rubber exposed to air tended to crumble.
I was able to repair this by spiraling electrical tape over the exposed section, then slipping heat shrink tube over the tape, to make it secure.

DanBress 08-13-2008 09:43 PM

Ok. I just did the test you suggested on an extension cord thats connected to a different outlet on a different circuit(that was on) and it passed the test.
it also reads "correct" on one of those little orange guys you plug in that tells if you are wired correctly.

in the junction box in question

if i look at the first black wire
black to good neutral=118v
white to good neutral = 0v, O ohm

other black to good neutral = 0v
other white to good neutral = .264V, 2.65M Ohm ?? is this a concern?

box to neutral shows 0 OHM

Wildie 08-13-2008 10:13 PM

The white with the 'foreign' potential goes to the switch box, you believe.
Then two cables leave the switch box. one to the other room and one to the over-head light.
If you open the whites in the switch box, you should be able to ascertain if the 'foreign' condition is coming from the light or the other room. Again, using your extension cord as a reference.
Make sure that everything is unplugged on this circuit and that all lamps are removed, to make sure that you are not reading feed-back through anything.

JohnJ0906 08-16-2008 07:18 PM

Quote:

Originally Posted by Wildie (Post 148597)
T
Make sure that everything is unplugged on this circuit and that all lamps are removed, to make sure that you are not reading feed-back through anything.

Just want to repeat this - make sure all loads are unplugged or otherwise disconnected, or it will affect your readings.


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