Electric cooking oven wiring issue?

[zendriver]

MIL has the typical low cost generic GE smooth top electric range. And, yes, I'm am no electrician.

When a guy installed a new gas furnace (after FIL passed (who did all wiring- maybe to code), the range oven quit working but the stove top continued to work fine. Everybody just assumed somehow a power surge or something trashed something in the Oven. It been two years and nobody has done anything with it, but they want it fixed or range replaced. I didn't get a chance to test it (maybe I was ignoring it) since it's in another town, but assumed maybe it was the control board (common failure), picked up a used one on eBay.

Popped it in, made no difference, so not suspecting that. I did try to take some voltage measurement from the three prong plug. Could not get down in it with the probes, but slightly pulling the plug out measure 240v (or so) across the hots but between neutral gets 240V (or so) on one side and about 2v on the other. I got the same measurements on the lugs where the cord connects. Would being connected make any difference or should they both still be 120v between hots an neutral?

I kind of said fug it at that point. (especially since the circuit breaker box has nothing marked), that they should either have the guy that did the install, or another electrician look at it, since maybe something was goofed in the wiring. We don't want to just replace the range and have a similar problem.

Does this make since that might be a reason the control board not turning on anything in the oven?

thanks for any input.

 

[BurtEggley]

First, I'd turn the breakers off before letting anyone near it again. Sounds like the neutral is shorted to hot on one leg, which if so the cabinet itself may be hot to ground and able to kill. You should have somewhere between 120V - 123V between either leg and neutral, with 240V to 247V between the two legs (which you do). There should be zero, or close to it, volts between neutral and ground (probably you will get 120V if you test between ground and neutral, but I would suggest staying away from it while the breakers are turned on until you find where the mistake in wiring is - assuming again, that you tested accurately. If the neutral was simply open and not connected, it might have 120V on it but the fact that it has 240V, if your testing is accurate, then it tells me that the neutral is carrying the leg that you are getting 2V on. I am not an electrician but highly suggest you contact one, and turn it off until the problem is resolved. I might add, there are often spills on a residential kitchen floor, people lean on the corners of a range sometimes, there are pipes and sinks, and people come into their home kitchen barefoot. IF the cabinet is also hot, then they are dead if they make the right connection, and your problems will be a lot more than a malfunctioning range.

 

[Wrench97]

It's a 3 prong plug so first question is the 3rd a neutral or a ground?
Go down and look in the breaker box see if the wire is bare copper or white, while you are there make sure the breaker has 120v on each leg.
You may find a bad breaker, loose breaker or damaged bus bar if not 120 on each leg.

 

[wyliesdiesels]

MIL has the typical low cost generic GE smooth top electric range. And, yes, I'm am no electrician.

When a guy installed a new gas furnace (after FIL passed (who did all wiring- maybe to code), the range oven quit working but the stove top continued to work fine. Everybody just assumed somehow a power surge or something trashed something in the Oven. It been two years and nobody has done anything with it, but they want it fixed or range replaced. I didn't get a chance to test it (maybe I was ignoring it) since it's in another town, but assumed maybe it was the control board (common failure), picked up a used one on eBay.

unless the furnace is somehow on the same circuit as the range (shouldnt be), that is just a coincidence

Popped it in, made no difference, so not suspecting that. I did try to take some voltage measurement from the three prong plug. Could not get down in it with the probes, but slightly pulling the plug out measure 240v (or so) across the hots but between neutral gets 240V (or so) on one side and about 2v on the other. I got the same measurements on the lugs where the cord connects. Would being connected make any difference or should they both still be 120v between hots an neutral?

need to measure with the range unplugged as this could be a bad neutral connection since its an MWBC- multi-wire branch circuit

if you have 242v phase to phase and 240v hot to neutral on one phase and 2v hot to neutral on the other phase thats a classic sign of a bad neutral

to test with range unplugged you could pull the receptacle out and test to the lug terminals

I kind of said fug it at that point. (especially since the circuit breaker box has nothing marked), that they should either have the guy that did the install, or another electrician look at it, since maybe something was goofed in the wiring. We don't want to just replace the range and have a similar problem.

Does this make since that might be a reason the control board not turning on anything in the oven?

thanks for any input.

If the neutral is bad and sent 240v or 2v to the board instead of 120v then yes. hopefully, the board isnt fried and just not getting enough voltage to work....

 

[wyliesdiesels]

First, I'd turn the breakers off before letting anyone near it again. Sounds like the neutral is shorted to hot on one leg, which if so the cabinet itself may be hot to ground and able to kill.

This is possible but unlikely. more likely scenario is bad neutral and since its an MWBC it has the voltage its showing due to running thru the range. need to test with range unplugged.

You should have somewhere between 120V - 123V between either leg and neutral, with 240V to 247V between the two legs (which you do). There should be zero, or close to it, volts between neutral and ground (probably you will get 120V if you test between ground and neutral,

Its a 3 prong plug/recep so there is no ground. NEMA 10-50 has 2 hots 1 neutral. there is no ground to test to.

but I would suggest staying away from it while the breakers are turned on until you find where the mistake in wiring is - assuming again, that you tested accurately. If the neutral was simply open and not connected, it might have 120V on it but the fact that it has 240V, if your testing is accurate, then it tells me that the neutral is carrying the leg that you are getting 2V on. I am not an electrician but highly suggest you contact one, and turn it off until the problem is resolved. I might add, there are often spills on a residential kitchen floor, people lean on the corners of a range sometimes, there are pipes and sinks, and people come into their home kitchen barefoot. IF the cabinet is also hot, then they are dead if they make the right connection, and your problems will be a lot more than a malfunctioning range.

or its a bad neutral and since its an MWBC he is measuring the neutral thru the 2 phases. which is why the range needs to be unplugged for proper testing and troubleshooting

 

[wyliesdiesels]

It's a 3 prong plug so first question is the 3rd a neutral or a ground?
Go down and look in the breaker box see if the wire is bare copper or white, while you are there make sure the breaker has 120v on each leg.
You may find a bad breaker, loose breaker or damaged bus bar if not 120 on each leg.

NEMA 10-50 does not have a ground terminal. should be neutral. There has never been a range receptacle that has 2 hots and ground.

 

[BurtEggley]

Hi Wylie. I am missing something here that you are seeing that I am not My thoughts first are about potential voltages that exist regardless what the fault is with that neutral, and what that fault turns out to be. A lot of circuits for ranges use aluminum wires for example. There could be a loose or corroded connection anywhere that aluminum wire is bonded thru a connector - we don't know how that circuit was installed. Is it anchored with the proper aluminum anti-ox, or is it a couple wires twisted together inside a twist-on connector to tie it into another kitchen circuit. What gauge is it?

To me, the voltage numbers he got imply that the neutral has potential above ground. If that is so, and the chassis is bonded to the neutral, like it should be on an older 3 prong plug, the chassis will also have potential. I understand that the plug may not have formal a ground wire, but is that relevant if a person with one hand on the range touches something in that kitchen that is grounded, including bare feet on the floor.

Right now I do not believe that range is safe to be around, and recommend the breakers be turned off and it unplugged until the fault is located. The fault is likely to be something back at the panel, but it may be something completely unrelated including inside the receptacle, or even in the stove. The potentials are uneven, and that concerns me. Maybe one of the elements broke and is somehow shorted to the chassis combined with an open or corroded aluminum neutral. I just don't know and would advise backing away from it until the power is off and the unit unplugged. He said he has trouble getting to the plug etc..

 

[wyliesdiesels]

Hi Wylie. I am missing something here that you are seeing that I am not My thoughts first are about potential voltages that exist regardless what the fault is with that neutral, and what that fault turns out to be. A lot of circuits for ranges use aluminum wires for example. There could be a loose or corroded connection anywhere that aluminum wire is bonded thru a connector - we don't know how that circuit was installed. Is it anchored with the proper aluminum anti-ox, or is it a couple wires twisted together inside a twist-on connector to tie it into another kitchen circuit. What gauge is it?

Anti-ox is not required by code unless manufacturer calls for it

To me, the voltage numbers he got imply that the neutral has potential above ground. If that is so, and the chassis is bonded to the neutral, like it should be on an older 3 prong plug, the chassis will also have potential. I understand that the plug may not have formal a ground wire, but is that relevant if a person with one hand on the range touches something in that kitchen that is grounded, including bare feet on the floor.

Correct. If the neutral is compromised, it would have potential above ground and someone could get shocked if they touch the chassis and a say a faucet connected to a bonded metal water line.

Right now I do not believe that range is safe to be around, and recommend the breakers be turned off and it unplugged until the fault is located. The fault is likely to be something back at the panel, but it may be something completely unrelated including inside the receptacle, or even in the stove. The potentials are uneven, and that concerns me. Maybe one of the elements broke and is somehow shorted to the chassis combined with an open or corroded aluminum neutral. I just don't know and would advise backing away from it until the power is off and the unit unplugged. He said he has trouble getting to the plug etc..

It wouldnt be inside the stove since he gets these voltage readings at the receptacle

 

[75gmck25]

Since the furnace guy may have had to do something with the panel, which included moving breakers or other work, I would check that panel and breaker install first. Make sure the stove/range wiring is properly connected to the breaker, and the breaker is properly inserted and making a good connection to the bus. Sometimes it’s hard to see if a 240 volt dual breaker is completely seated and making good connections.

 

[Codyboy]

Classic voltage for an open neutral as wyliediesels said.
The guy probably forgot to connect the neutral at the panel or its loose.

 

[BurtEggley]

Classic voltage for an open neutral as wyliediesels said.
The guy probably forgot to connect the neutral at the panel or its loose.

"I did try to take some voltage measurement from the three prong plug. Could not get down in it with the probes, but slightly pulling the plug out measure 240v (or so) across the hots but between neutral gets 240V (or so) on one side and about 2v on the other."

Hard for me to see that. The prongs go into the receptacle then back thru their wires to the panel. That would imply that one side of the panel has 240V between neutral and a hot, and the other side 2V between neutral and a hot. Please explain the electrical potentials he is getting. One leg sees the other (240V) but the other leg (2V) does not. There are not two neutral wires from that prong back to the panel or range. If the meter is seeing 240V leg one to leg two thru the combined neutral, would not measuring in reverse, leg two to leg thru the combined neutral read the same?

 

[Codyboy]

Hard for me to see that. The prongs go into the receptacle then back thru their wires to the panel. That would imply that one side of the panel has 240V between neutral and a hot, and the other side 2V between neutral and a hot. Please explain the electrical potentials he is getting. One leg sees the other (240V) but the other leg (2V) does not. There are not two neutral wires from that prong back to the panel or range. If the meter is seeing 240V leg one to leg two thru the combined neutral, would not measuring in reverse, leg two to leg thru the combined neutral read the same?

Open neutrals do weird ****.
240 circuits with a load and no neutral will have a difference in voltage from one leg to the other and could read up to line voltage from the neutral to a leg.

Remove all load and it balances back out.
Thats why you have to unplug it.

ETA
Adding load to a suspected open neutral is how you troubleshoot the issue.
Keep moving back toward the source and checking voltage until you find good voltage. The issue is between the good voltage and bad voltage, whether thats a cut wire or termination along the way.

ETA 2
I can draw out a picture if that would help you understand.

 

[zendriver]

They were having a hard time getting an electrician wanting to do this small job.

I tasked wife to coax retired BIL, who has cognitive issues, (but was the electrical guy for a lumber company his whole career) to take a look. Apparently it was a loose or out of whack neutral wire, or some other simple fix. We all feel bad for not tackling it sooner, but that the way it goes sometimes. I told them they owe me a cake. I received cred for my troubleshooting to what problem was not.

Thanks YouTube and thanks to you all, for your valuable input.

 

[Codyboy]

Good. At least its fixed!

 

[wyliesdiesels]

Hard for me to see that. The prongs go into the receptacle then back thru their wires to the panel. That would imply that one side of the panel has 240V between neutral and a hot, and the other side 2V between neutral and a hot. Please explain the electrical potentials he is getting. One leg sees the other (240V) but the other leg (2V) does not. There are not two neutral wires from that prong back to the panel or range. If the meter is seeing 240V leg one to leg two thru the combined neutral, would not measuring in reverse, leg two to leg thru the combined neutral read the same?

do some reading on open neutrals and look at the math involved. it will help you understand it better.

and the OPs issue turned out to be a bad neutral so....

 

[BurtEggley]

I suspect that the OP did not measure voltages as he stated. Further, I grasp the theory really well, doing college level work to prepare me for the major of electrical engineering in college. I also managed a regional electronic repair facility for Teledyne in my 20's. If all my friends' dads didn't lose their engineering jobs in 1968, I would have followed that path. At the time electrical and mechanical engineers were pumping gas in gas stations to feed their families. There was a glut of them after the space program, and aerospace spooled down. Engineers were a dime a dozen. To suffer in engineering classes for six years to end up pumping gas wasn't my idea of a career. But I have not forgotten the theory.

 

[Wrench97]

I suspect that the OP did not measure voltages as he stated. Further, I grasp the theory really well, doing college level work to prepare me for the major of electrical engineering in college. I also managed a regional electronic repair facility for Teledyne in my 20's. If all my friends' dads didn't lose their engineering jobs in 1968, I would have followed that path. At the time electrical and mechanical engineers were pumping gas in gas stations to feed their families. There was a glut of them after the space program, and aerospace spooled down. Engineers were a dime a dozen. To suffer in engineering classes for six years to end up pumping gas wasn't my idea of a career. But I have not forgotten the theory.

"New Math" in the 80's changed all those theories.........

 

[dave*99]

I suspect that the OP did not measure voltages as he stated. Further, I grasp the theory really well, doing college level work to prepare me for the major of electrical engineering in college. I also managed a regional electronic repair facility for Teledyne in my 20's. If all my friends' dads didn't lose their engineering jobs in 1968, I would have followed that path. At the time electrical and mechanical engineers were pumping gas in gas stations to feed their families. There was a glut of them after the space program, and aerospace spooled down. Engineers were a dime a dozen. To suffer in engineering classes for six years to end up pumping gas wasn't my idea of a career. But I have not forgotten the theory.

The original measurements looked very telling to most here.

The range was still attached to the circuit. The neutral was open. The 120V control circuitry was pulling the open neutral to with in 2V of the phase voltage.

Hence the OP measured nearly 240V between the leg not connected to the control board and the pulled up neutral.

 

[zendriver]

I suspect that the OP did not measure voltages as he stated. Further, I grasp the theory really well, doing college level work to prepare me for the major of electrical engineering in college. I also managed a regional electronic repair facility for Teledyne in my 20's. If all my friends' dads didn't lose their engineering jobs in 1968, I would have followed that path. At the time electrical and mechanical engineers were pumping gas in gas stations to feed their families. There was a glut of them after the space program, and aerospace spooled down. Engineers were a dime a dozen. To suffer in engineering classes for six years to end up pumping gas wasn't my idea of a career. But I have not forgotten the theory.

How do you "suspect" I measured?

There are only 3 contacts with markings pretty obvious..

 

[BurtEggley]

Your electrician found that the neutral was open in some way. That left two legs coming into the stove. When you measured between leg 1 and leg 2, you got the expected voltage of 240V. When you measured between one leg and neutral you got 240V again. This would imply that there was a short between the one of the legs and neutral during that measurement. It did not repeat when you measured 2V on the other. The clock, light, digital display etc., are running off one side of the 247V. But they are not enough of a load to be close to zero resistance and dead short. You also have the neutral wire that is open at one end before it was fixed acting like both a capacitor and an RF antenna. You will see that voltage too.

 

[dave*99]

This would imply that there was a short between the one of the legs and neutral.

Not a short. The control electronics provided that path (impedance) as described in the OPs details of his measurements.

 

[whateg01]

... This would imply that there was a short between the one of the legs and neutral.

No, it doesn't necessarily mean there's a short. It means there's a path.

(Other Dave was typing at the same time)

 

[dave*99]

This is the most classic example of what happens when a 120/240V appliance is connected to a circuit with an open neutral.

 

[Ryan]

Keep in mind that debating is fine and arguing is ********.

 

[mm08822]

Here's a quick example...assume 1 burner turned on and the clock/controller is powered up.
Left side all working ok.

Right side has open neutral, now both appliance loads in series acting as a voltage divider at the neutral wire in the stove (no longer connected to neutral in panel). Resulting current is based upon total series resistance across 240v. Current is now only flowing between L1/L2. (Clock/controller would soon be toast in this example.)

(Pick your favorite resistance values, but the concept doesn't change.)

 

[dave*99]

Here's a quick example...assume 1 burner turned on and the clock/controller is powered up.
Left side all working ok.

Right side has open neutral, now both appliance loads in series acting as a voltage divider at the neutral wire in the stove (no longer connected to neutral in panel). Resulting current is based upon total series resistance across 240v. Current is now only flowing between L1/L2. (Clock/controller would soon be toast in this example.)

(Pick your favorite resistance values, but the concept doesn't change.)

But the burner is not a 120V load. Not connected to neutral.

The OP had a control board as the 120V load. And it had no current path to supply neutral so it no worky
Once neutral was connected it worked.

 

[mm08822]

But the burner is not a 120V load. Not connected to neutral.

The OP had a control board as the 120V load. And it had no current path to supply neutral so it no worky
Once neutral was connected it worked.

Does it matter? Two loads in series across 240v vs both being fed with 120v as per design. Then those 2 connected loads get thrown in series. With different resistances between the 2, the voltages swing somewhere between 0 and 240 for each but total 240v.

So it was a controller and a light in series (or what ever). This was an example for BurtEggly and not the OP.

 

[dave*99]

Does it matter? Two loads in series across 240v vs both being fed with 120v as per design. Then those 2 connected loads get thrown in series. With different resistances between the 2, the voltages swing somewhere between 0 and 240 for each but total 240v.

So it was a controller and a light in series (or what ever). This was an example for BurtEggly and not the OP.

I understand your schematic. I can’t speak for Burt.

In the OPs case the only thing connected to the other side of the voltage divider circuit was his voltmeter and some cable capacitance. So nothing blew up and the voltage drop was 2V

 

[BurtEggley]

I am Ok with the word "path." It is much more accurate of what was in my mind. Choice of words was never my best subject. I am Ok with all the drawings, wonky is a good word too. My only thought is that 240V across the two legs, and then 240V again across a leg and neutral has to be a really low resistance on one of the legs. My own thoughts are that the burners are across 240V but it has been a long time since I worked on an electric stove or range. The clock, display, light, fan, etc., are probably 120V. Some would be on all the time but pretty high resistance I would think, unless maybe an incandescent light filament when it is cold. I think in trying to take the measurements in that tight space, on a plug that was part-in and part-out, maybe the probe touched more than one pin at a time on one of the readings. I am glad he has it working again, so will the people using it. I anticipated all along that the reading would be "wonky" with an open neutral. The 240V and 240V readings didn't seem right. I actually posted in this thread because when I read he had 240V between a leg and neutral, since the ground is bonded on these ranges, my concern was that the cabinet was hot with an open ground and neutral. Bare feet on damp kitchen floor and hot cabinet combination really concerned me. I've been bitten before, probably we all have, and it is not a good way to start ones day.

 

[wyliesdiesels]

I actually posted in this thread because when I read he had 240V between a leg and neutral, since the ground is bonded on these ranges, my concern was that the cabinet was hot with an open ground and neutral. Bare feet on damp kitchen floor and hot cabinet combination really concerned me. I've been bitten before, probably we all have, and it is not a good way to start ones day.

yes with an open neutral you can get bit with the neutral return current because of the chassis to neutral bonding in the back of the stove (and dryer) when using a 3-wire cord/plug/receptacle, under the right conditions. so you were spot on with this.

its one reason why i advocate so much in switching dryer and stove circuits to 4-wire.

 

[dave*99]

My only thought is that 240V across the two legs, and then 240V again across a leg and neutral has to be a really low resistance on one of the legs.

Nope. The voltage divider is the voltmeter with its 10 Megohm input impedance and the control board electronics. So even if the board was 1000 ohms the 2V reading is legit.

 

[BurtEggley]

its one reason why i advocate so much in switching dryer and stove circuits to 4-wire.

Wylie - makes sense to me. In fact, we made that conversion on the dryer a long time ago. I am of an age where I remember 120V appliances in the house that would nip someone if the plug was in the wrong way.

 

[wyliesdiesels]

Wylie - makes sense to me. In fact, we made that conversion on the dryer a long time ago. I am of an age where I remember 120V appliances in the house that would nip someone if the plug was in the wrong way.

yup. that is why polarized plugs were adopted as well as not bonding the neutral to the chassis. we have come a long way in the electrical safety world.

house wives used to get zapped when the vacuum was plugged in the wrong way...