Open neutral found. Now what?

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Old 02-08-16, 10:33 AM
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Open neutral found. Now what?

I have an open neutral between my breaker box and my oven/stove's 220v outlet. Can I run a single #8 white insulated wire along the existing 8-3 Romex, or do I have to take out the existing 8-3 Romex and replace all of it? I would rather spend $40 vs $120 if it is allowed.

Jason
 
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Old 02-08-16, 11:03 AM
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No, you can't run a single THHN or equal outside of conduit.

But 8ga wire just doesn't go open on it's own without some kind of damage unless there's some kind of weird manufacturing defect. I assume you ruled out a connection problem at both ends? I'd be looking for a damaged area, perhaps a nail or poorly applied cable clamp. If you find a problem, you can repair the damage. If there's no slack anywhere it might take two boxes and a short length of cable, but still cheaper/easier than running new.
 
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Old 02-08-16, 12:25 PM
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The initial problem was when the baking element of the oven melted. I don't know if when it melted it caused problems down the line. I have hand traced entire run and do not see any damage. It was run through the floor joist and I don't see any clamps.
 
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Old 02-08-16, 12:43 PM
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Usually an element will short to ground. The neutral doesn't even carry the load.
Did the breaker trip and what size is it ?

You should measure 240v across L1 and L2
You should measure 120v from L1 to neutral or to ground.
You should measure 120v from L2 to neutral or to ground.

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Old 02-08-16, 01:10 PM
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This is what my plug looks like. I have 240v across L1 to L2. I have zero measuring from L1 or L2 to neutral. I have measured through the outlet and also with the wires removed from the outlet.

The breaker is 50A and did not trip. I also cycled the breaker several times. I checked for loose wires in the outlet and in the panel. The screws on the breaker and the neutral bar were all very tight.

I have removed the three wires from the breaker panel (with the entire panel shut off) and checked for continutity. With my leads clipped to the white and black wire at the outlet I showed an open when I touch the white and black wires at the breaker panel. With the leads clipped to the black and red wire at the outlet I had continutity when I held the red and black wires together at the breaker panel.
 
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Old 02-08-16, 01:14 PM
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CORRECTION: The breaker is 40amp. I just looked at the picture I took of the panel.
 
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Old 02-08-16, 02:29 PM
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Well it does sound like you have an open white then. Kind of scary that the breaker didn't trip.

I think you will need to pull new cable, and while you are at it, use 8/3 w/g and replace your 3 slot receptacle with a 4 circuit so you will up to code. Replace the cord set and remove the ground/neutral jumper.

And replace that breaker! (What brand is it...FPE?)
 
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Old 02-08-16, 06:05 PM
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If entire length, or most of the cable is accessible, try this to find bad section.

Disconnect oven.
Disconnect both hot (L1 and L2) from the breaker and connect them to ground.
Disconnect neutral.
Connect neutral to hot (either L1 or L2 of the breaker).

Use non-contact tester to trace the line. If should stop beeping where the wire is damaged.

The reason I'm telling you to connect L1 and L2 to ground is because some times non-contact tester gives false reading because disconnected wires next to hot wire can get some voltages induced by hot wire next to it.

If you have a toner you can use that to trace as well.



Still, I don't see how 8 AWG wire can be damaged to the point it is completely open (melted through?), yet cannot see damage on the wire.

Are you sure there is no damage in breaker panel or the outlet?
 
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Old 02-08-16, 07:39 PM
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You said you had 8-3 romex in your opening post. Then you said during testing you had red, white and black. Where is the bare ground ? If you have 8-3 there should be a bare ground and you should be using a 4 prong plug.
 
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Old 02-08-16, 07:58 PM
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When was the 8-3 NM cable installed? Up into the early '80s 8-3 plain (w/o ground) was available and widely used for range circuits. Have you opened the range receptacle and checked voltage at the wire ends? It would be very very rare to find the neutral conductor open in a length of NM cable. 4-wire circuits, receptacles and range cords weren't required till the 1996 NEC.
 
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Old 02-08-16, 09:17 PM
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My house was built in 1987 and the cable to the range is type SE, possibly even aluminum. Amazingly, the clothes dryer circuit was wired with 10-3 w/g although it has a 10-30 receptacle. Some day I will change it for a four-wire receptacle but since my washer and dryer use 240 volts only it is a fairly low priority.

I do wonder why Carbide thinks the circuit breaker should have tripped? Since the neutral only carries the unbalanced load, and a kitchen range is mostly balanced, there is no reason that I can think of for the CB to trip, unless this range has a GFCI circuit breaker.
 
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Old 02-09-16, 03:19 AM
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Your dryer uses 120 volts for the motor and lights. The heater is 240 volts.
 
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Old 02-09-16, 06:17 AM
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Your dryer uses 120 volts for the motor and lights. The heater is 240 volts.
Are you referring to me, PC? Because if you are, you are wrong. My laundry set is made in Sweden by Asko and is straight 240 volts. Dryer plugs into the 240/120 volt 10-30 receptacle and the washer plugs into the dryer. The arrangement is not uncommon with European laundry appliances.
 
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Old 02-09-16, 08:12 AM
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All indications are so far that the neutral must have melted open, probably due to the shorted element. The neutral is carrying the fault current in this case because of no ground. Since there is no physical damage to the cable and the end connections are all good, it seems likely the neutral melted. If that's the case, the breaker certainly should have blown.

As I mentioned earlier, it's possible there was an installation problem or manufacturing defect so there was a weak spot in the neutral that opened up like a fuse before the breaker tripped, but so far there is no evidence of that.
 
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Old 02-09-16, 08:57 AM
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If the #8 conductor is completely opened mid-run there must be a serious injury to the cable somewhere -- perhaps a framing nail driven through it or a significant manufacturing defect. Fusing current on undamaged #8 is nearly 500A, no way that happened on a residential service, and if it did would produce more than enough heat to start a fire. Is there perhaps a hidden junction box somewhere on the range circuit? This is more consistent with a failed wire nut.
 
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Old 02-09-16, 11:18 AM
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All indications are so far that the neutral must have melted open, probably due to the shorted element
I don't think so.

Is there perhaps a hidden junction box somewhere on the range circuit? This is more consistent with a failed wire nut.
That is what I would be looking for.
 
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