[shardy]

Hello,

I have wall oven that has ceased to function some time ago. After multiple service tech visits, today they determined that the issue is my house wiring, which I don't completely believe yet and am looking for the thoughts of others.

The tech pulled the oven today, disconnected the wire whip from the terminal blocks and then we measured the voltages at the wire whip:
L1-Ground = 120V
L2-Ground = 120V
L1-L2 = 240V
Perfect, just as it should be right?

He reconnects them to the oven terminal block and now we have new voltages:
L1-Ground = 240V
L2-Ground = 0V
L1-L2 = 240V

The tech called in to some tech support line and explained it all -- their answer is that those voltages measured at the whip without the oven connected are invalid because there's no load attached to it and thus the ground can be floating. Thus, their conclusion is that the oven is fine and it's the house wiring that is faulty (nevermind the fact it worked for 10 months with this oven and 13 years with the previous oven).

While I agree that the DMM doesn't represent much of a load, my hypothesis is that somewhere in the oven, L2 is shorted to ground and that's why we're getting the readings above.

I'd welcome any thoughts anyone has on this, as well as any tips on isolating my suspected short (I guess just resistance test every connection on L2 to the metal cage?).

Thanks!

 

[gregzoll]

Is this three wire or four wire? If a leg is shorted to ground, the Circuit Breaker would have tripped, or if a fuse, the fuse would have blown. I you get voltage inside the junction box, tell the tech to go take a hike. If that number he called was someone at his shop. Looks like both need to learn how to use a meter.

Newer ovens now require 4 wire, because they use 120 for the computer board and light, 240 for the elements.

 

[Oso954]

Someone needs to inspect/take readings at your breaker. I can understand the tech not doing it. If you are not comfortable in doing it, you can get an electrician. I suspect a bad breaker or contact.

 

[shardy]

It is 4 wire - red, white, black, and ground. The readings were taken just at the terminals on the back of the oven, I'll re-read them tonight at the breaker. The breaker has never tripped during all of this, so, that may help rule out a short to ground somewhere.

Is there anything in particular I should look for at the breaker that would indicate what the problem is?

Thanks again.

Steve

 

[joed]

Those readings to me indicate an open ground to the stove and a ground possibly connected to L2.
You say it's a 4 wire feed. What are the voltages to neutral? What type of meter is being used? It should be a solenoid type tester that applies a load so you don't get phantom voltages, commonly called a wiggy after a popular brand.

 

[Jump-start]

Is this three wire or four wire? If a leg is shorted to ground, the Circuit Breaker would have tripped, or if a fuse, the fuse would have blown. I you get voltage inside the junction box, tell the tech to go take a hike. If that number he called was someone at his shop. Looks like both need to learn how to use a meter.

A fuse or double pole breaker with handle ties does not give common trip so its possible L-2 to be dead while L-1 is still live.

Newer ovens now require 4 wire, because they use 120 for the computer board and light, 240 for the elements.

No. Some ovens have always required 120 in addition to 240. Prior to 1996 the code let you ground through the neutral hence why 3 wires were allowed up to 120/240 appliances.

 

[joed]

A fuse or double pole breaker with handle ties does not give common trip so its possible L-2 to be dead while L-1 is still live.

You would not be able to get a 240volt reading if that was true. You might still get 120 from each to ground but not 240 between them.

 

[Jump-start]

You would not be able to get a 240volt reading if that was true. You might still get 120 from each to ground but not 240 between them.

Correct, but you would still get voltage. Greg had it worded as all or nothing which was misleading the OP. So even though Greg will thank your post making me look wrong, he is still incorrect.

 

[gregzoll]

You would not be able to get a 240volt reading if that was true. You might still get 120 from each to ground but not 240 between them.

So true. Unless the OP states if this is two Single breakers with or without a tie, or a double with a single throw, it could happen in theory, but you would be smelling some Magic Smoke if it happened. Only seen a single breaker with a handle tie, that one side tripped, the other stayed engaged.

 

[Jump-start]

So true. Unless the OP states if this is two Single breakers with or without a tie, or a double with a single throw,

How does "double with a single throw" come into this? Its called a 2 pole common trip breaker and you would have figured that out years ago if you didnt have every electrician on your ignore list:

http://www.diychatroom.com/f18/240-v-breaker-switch-many-colours-286818/#post2198218

http://www.diychatroom.com/f18/240-v-breaker-switch-many-colours-286818/#post2199562

it could happen in theory, but you would be smelling some Magic Smoke if it happened. Only seen a single breaker with a handle tie, that one side tripped, the other stayed engaged.

So in every other case a handle tie will always kick off the other side? Yahhh ok.

 

[joed]

Still waiting for voltages to neutral instead of ground.

 

[Jump-start]

Still waiting for voltages to neutral instead of ground.

x2

That will clear up confusion.

 

[Jim Port]

x2

That will clear up confusion.

Maybe not for all. :vs_no_no_no:

 

[shardy]

Sorry for the delay, I was out of town and other things got in the way.

Techs came back out and re-measured and I had them check voltages to neutral as well. In short, got the same as before, and also checked neutral to ground and got 120V. We disconnected the neutral supply from the oven and checked its voltage to ground, 0V. Disconnected everything from the oven and checked supply and got 120V L1 to ground, 120V L2 to ground, 240V L1 to L2, 0V neutral to ground. Now, these were with a standard DMM, not a solenoid type. However, after this, even the techs agree it's a problem with the oven and not the supply. Unfortunately, the corporate customer service doesn't agree and still wants an electrician to come out.

 

[brric]

Sorry for the delay, I was out of town and other things got in the way.

Techs came back out and re-measured and I had them check voltages to neutral as well. In short, got the same as before, and also checked neutral to ground and got 120V. We disconnected the neutral supply from the oven and checked its voltage to ground, 0V. Disconnected everything from the oven and checked supply and got 120V L1 to ground, 120V L2 to ground, 240V L1 to L2, 0V neutral to ground. Now, these were with a standard DMM, not a solenoid type. However, after this, even the techs agree it's a problem with the oven and not the supply. Unfortunately, the corporate customer service doesn't agree and still wants an electrician to come out.[/quote
deleted

 

[shardy]

I'm pulling this from memory, but I believe I had 240V from one of the hots to neutral and 0V from the other to neutral. This is with the oven connected; if I disconnect the oven from the supply, I get everything as it should be.

 

[dmxtothemax]

I think you have a high
Resistance connection
On your L2 line !
Under little or no load
Enough current will flow
To take a reading
on a volt meter
But when any real
current is needed
then the faulty joint
Becomes high resistance
Or open circuit !