Need Oven Wiring Confirmation

[DC73]

Helping some friends who are installing a new double oven and would like to pick the guru's brains on proper wiring.

The new oven has 4 wires. The existing house wiring for the oven circuit is 3 wires (one black, one white, one bare ground). The bare ground is inside the sheathing for the wire bundle and is smaller than the two insulated conductors.

The old oven also had 4 wires and had both the ground and neutral conductors from the oven tied to the bare copper ground from the wall.

The instructions for the new oven show it is permissible to connect it to a 3 wire circuit from the house by connecting it the same as the old oven. BUT, the diagram in the instructions references the third wire coming from the wall as being a neutral with no mention in the instructions at all about what to do if it is a bare ground.

It will not be a fun project to pull new wire to the oven location. I haven't verified the power requirements yet for the new oven so this might be all for naught if it requires more than a 30A circuit which is what is currently installed.

Questions:

1) The old oven worked fine and I suspect the new one will as well but are there any concerns about connecting the new one to the house wiring using that bare ground instead of an insulated neutral?

2) I know it would be better to have 4 wires coming from the wall. Is it okay to just add a 4th wire by installing a single insulated neutral from the panel to the oven location? Again, this won't be fun but would be easier than a new wire bundle because there is room in an existing hole in the top plate above the panel for a single wire but not a new wire bundle. The roof is at a very low angle above this panel and makes working in the attic above the panel difficult at best.

3) I know that ovens can be hard wired but it would be a lot easier if we could install a proper plug. Is there an upper limit on power requirements for ovens before hard wiring becomes mandatory?

4) The existing house wiring exits the wall through a hole in the sheetrock without a junction box. It was connected to the old oven wiring with both wire nuts and tape but just left behind the oven without the benefit of a junction box. If we install a proper plug and cord, it will all get changed. But, if we hard wire the oven, is a junction box required to hide the connections since the wires will be inaccessible behind the oven?

Thanks much,

DC

 

[larry4406]

The sparky’s will be along soon.

My understanding is that if you are just replacing the appliance, then you can wire it with the old 3-wire method where ground and neutral are one and the same. There should be a copper strip internal to the oven connecting the chassis to the neutral lug.

If you were relocating the appliance, then you need to pull a new 4-wire feed, make sure the oven bonding strip is removed, etc.

I’m going thru this now with kitchen renovation.

 

[Bert_]

Two hots and a ground has never been acceptable. Used to be able to run two hots an a neutral. Common methods would be 6-3 Romex without ground or #6 se cable with a bare neutral.


6-2 with ground or similar is wrong no matter when it was installed

 

[Bert_]

Delete

 

[Norcal]

If it a SE type cable & fed from the main panel not a sub panel, connect the grounding & neutral conductors to the bare neutral, if the neutral is not connected it will not be a good thing, if connected to a 2 conductor w/ ground cable it needs to be brought up to code w/ a 4 wire feed. Is the uninsulated conductor solid or stranded? Photos always help.

 

[nadogail]

Check he panel feeding the Oven; I will bet that the Neutral and the ground are connected together.

 

[DC73]

Is the uninsulated conductor solid or stranded?

It's solid. I didn't get a chance to verify the wire gauge but it looks like a romex type 10/2 w/gnd.

The panel is the only breaker panel for the house and it's in the garage but the main disconnect is on the back of the house.

DC

 

[walta]

Seems to me the first step is to read the installation instructions, find the electrical requirements.

The instructions may well include an approved way to connected the appliance to the 3 wires you described.

Once you know what is required then decide if the existing wires are capable of supply what is required.

Then make sure the breaker feeding the wire is sized at or above the minimum required and not larger than the maximum allowed for this appliance while still protecting the wire from being overloaded.

Walta

 

[Norcal]

If solid sounds like NM cable, not compliant & never was.

 

[Jim_No_Garage]

If solid sounds like NM cable, not compliant & never was.

The dead wall oven I pulled and installed a replacement for had solid NM to a box mounted in the wall oven cabinet/cavity and then the oven had a "BX-like" whip with stranded wires that you ran to the box, connected and then slid the oven back into place.

The box is "accessible" if you remove the oven from the cabinet/cavity. The original install was inspected as part of the back to the studs gut and redo of the kitchen with full permits so it passed inspection here in 2001. It WAS a 4 wire connection at that time.

Jim

 

[Showkey]

^^^^^^^^^^^^^^^^^
Common connection in my area as well. Sometimes if the cavity is tight, the box is in the basement and the “BX whip“ is long enough to allow the oven to slide out.

 

[billconner]

I'm a little surprised the amperage for a single wall oven is sufficient for a double, but last wall oven I installed was fine on a 240 20amp circuit.

I'd ask building department if bare ground is adequate. I don't think it is, but not positive.

Romex to a junction box is fine, just not to oven terminals, and I think you know that.

 

[DC73]

Seems to me the first step is to read the installation instructions, find the electrical requirements.

The instructions were read before I ever posted. See my first post, paragraph 4. The instructions have no information about what do if the third wire is a smaller bare copper wire instead of a true insulated neutral. It just shows a connection diagram with the third wire from the house being labeled as a "neutral". The instructions also say to get the wattage information from the appliance which I haven't had a chance to do yet. That will likely come later today or tomorrow.

I sure wish someone would tackle the 4 questions in my first post in order. In addition to helping with the project, the answers may very well benefit someone else down the road who reads this thread.

DC

 

[DC73]

I'm a little surprised the amperage for a single wall oven is sufficient for a double, but last wall oven I installed was fine on a 240 20amp circuit.

I'd ask building department if bare ground is adequate. I don't think it is, but not positive.

Romex to a junction box is fine, just not to oven terminals, and I think you know that.

I'll hopefully be able to verify the power requirements some time this weekend but you may very well be correct that what's existing isn't enough for a double oven.

And, yes, I know romex all the way to the oven terminals is not acceptable.

DC

 

[billconner]

ok
1. I don't believe the bare ground in Romex can be used for neutral.
2. Probably no - I don't think a single insulated conductor can be used for a neutral. Maybe there is a wire type like a 10/1 Romex I don't know of but it's not THHN.
3. There are receptacles and plugs but I think a junction box makes more sense. With amperage, voltage, and number of wires, easy to pick correct plug from a NEMA chart. https://www.americord.com/pub/media/wysiwyg/Qualtek_nema_nonlocking_configuration_chart_2.png
4. See 3 above. Box recommended but plug ok. Do not leave tape and wire nuts exposed, even if behind oven.
You'd be best pulling a proper new feed. I often try to get by without upgrading - plumbing, electrical, carpentry, etc. - but this seems below too compromised.

 

[Norcal]

I'm a little surprised the amperage for a single wall oven is sufficient for a double, but last wall oven I installed was fine on a 240 20amp circuit.

I'd ask building department if bare ground is adequate. I don't think it is, but not positive.

Romex to a junction box is fine, just not to oven terminals, and I think you know that.

The problem is you cannot use a grounding conductor as a neutral, if a appliance has a neutral connection that means there are items requiring 120 volts, such as the oven light, controls, & so on.

 

[Showkey]

Double wall ovens are typically 40 amps (240v).

 

[wyliesdiesels]

Helping some friends who are installing a new double oven and would like to pick the guru's brains on proper wiring.

The new oven has 4 wires. The existing house wiring for the oven circuit is 3 wires (one black, one white, one bare ground). The bare ground is inside the sheathing for the wire bundle and is smaller than the two insulated conductors.

The old oven also had 4 wires and had both the ground and neutral conductors from the oven tied to the bare copper ground from the wall.

The instructions for the new oven show it is permissible to connect it to a 3 wire circuit from the house by connecting it the same as the old oven. BUT, the diagram in the instructions references the third wire coming from the wall as being a neutral with no mention in the instructions at all about what to do if it is a bare ground.

It will not be a fun project to pull new wire to the oven location. I haven't verified the power requirements yet for the new oven so this might be all for naught if it requires more than a 30A circuit which is what is currently installed.

Questions:

1) The old oven worked fine and I suspect the new one will as well but are there any concerns about connecting the new one to the house wiring using that bare ground instead of an insulated neutral?

2) I know it would be better to have 4 wires coming from the wall. Is it okay to just add a 4th wire by installing a single insulated neutral from the panel to the oven location? Again, this won't be fun but would be easier than a new wire bundle because there is room in an existing hole in the top plate above the panel for a single wire but not a new wire bundle. The roof is at a very low angle above this panel and makes working in the attic above the panel difficult at best.

3) I know that ovens can be hard wired but it would be a lot easier if we could install a proper plug. Is there an upper limit on power requirements for ovens before hard wiring becomes mandatory?

4) The existing house wiring exits the wall through a hole in the sheetrock without a junction box. It was connected to the old oven wiring with both wire nuts and tape but just left behind the oven without the benefit of a junction box. If we install a proper plug and cord, it will all get changed. But, if we hard wire the oven, is a junction box required to hide the connections since the wires will be inaccessible behind the oven?

Thanks much,

DC

was the existing oven 240v only?

If so then the existing wiring was compliant for that oven but a new 4-wire oven will need a new 4-wire circuit since the third wire is uninsulated.

 

[wyliesdiesels]

The sparky’s will be along soon.

My understanding is that if you are just replacing the appliance, then you can wire it with the old 3-wire method where ground and neutral are one and the same. There should be a copper strip internal to the oven connecting the chassis to the neutral lug.

If you were relocating the appliance, then you need to pull a new 4-wire feed, make sure the oven bonding strip is removed, etc.

I’m going thru this now with kitchen renovation.

that only works when the third wire is an INSULATED conductor NOT a bare conductor. you cannot be neutral current on a bare conductor.

 

[wyliesdiesels]

Check he panel feeding the Oven; I will bet that the Neutral and the ground are connected together.

thats not the issue here. the issue is the third conductor is uninsulated. you cannot put neutral return current on a bare conductor

EDIT: since he has a subpanel (see post #7 above), your point is moot....

 

[wyliesdiesels]

It's solid. I didn't get a chance to verify the wire gauge but it looks like a romex type 10/2 w/gnd.


The panel is the only breaker panel for the house and it's in the garage but the main disconnect is on the back of the house.

DC

that means the panel is a subpanel and thus this circuit was NEVER compliant as neutral and ground are separated in a subpanel.

you need to run a new 4-wire circuit.

 

[wyliesdiesels]

Seems to me the first step is to read the installation instructions, find the electrical requirements.

The instructions may well include an approved way to connected the appliance to the 3 wires you described.

Once you know what is required then decide if the existing wires are capable of supply what is required.

Then make sure the breaker feeding the wire is sized at or above the minimum required and not larger than the maximum allowed for this appliance while still protecting the wire from being overloaded.

Walta

not when the third conductor is uninsulated... cant put neutral return current on that.

 

[wyliesdiesels]

I'm a little surprised the amperage for a single wall oven is sufficient for a double, but last wall oven I installed was fine on a 240 20amp circuit.

I'd ask building department if bare ground is adequate. I don't think it is, but not positive.

Romex to a junction box is fine, just not to oven terminals, and I think you know that.

a bare ground wire can ONLY be used as a ground wire. no neutral current or connection. thus the wire the OP has is not useable

The instructions were read before I ever posted. See my first post, paragraph 4. The instructions have no information about what do if the third wire is a smaller bare copper wire instead of a true insulated neutral. It just shows a connection diagram with the third wire from the house being labeled as a "neutral". The instructions also say to get the wattage information from the appliance which I haven't had a chance to do yet. That will likely come later today or tomorrow.

I sure wish someone would tackle the 4 questions in my first post in order. In addition to helping with the project, the answers may very well benefit someone else down the road who reads this thread.

DC

I can:

1) yeah the oven will work on the existing circuit but youre creating a dangerous hazard putting neutral return current on a bare conductor. this is NOT code compliant and never was IF the existing oven is 120/240v. only way it would have been compliant is if the existing oven was 240v ONLY (meaning no 120v components)

2) no, code does not permit you to do that and furthermore the existing circuit wires may be too small

3) max size nema plug you can get is 60a but i doubt your oven is 60a

4) that wasnt ever code compliant. splices need to be in a j box.

 

[DC73]

a bare ground wire can ONLY be used as a ground wire. no neutral current or connection. thus the wire the OP has is not useable

I can:

1) yeah the oven will work on the existing circuit but youre creating a dangerous hazard putting neutral return current on a bare conductor. this is NOT code compliant and never was IF the existing oven is 120/240v. only way it would have been compliant is if the existing oven was 240v ONLY (meaning no 120v components)

2) no, code does not permit you to do that and furthermore the existing circuit wires may be too small

3) max size nema plug you can get is 60a but i doubt your oven is 60a

4) that wasnt ever code compliant. splices need to be in a j box.

Perfect response. Thank you. I was hoping you would chime in. I've appreciated your advice in the past.

To clarify: When the house was built, the original oven was 240V only. When my friends bought the house, they replaced the original oven and that replacement oven had 4 wires. Whoever connected that oven simply used the existing house wiring by connecting the oven's neutral and ground wires together and to the bare copper ground from the wall. Fast forward many years and they are replacing the oven with a double oven.

Since my last post, I've learned the new oven is rated at 7400 watts so even though that's only a shade over 30A, it means the existing circuit won't work anyway and we'll be pulling in all new wire. I hate it for them because the cost of new wire alone is going to run nearly $300 and that really wasn't in the budget.

Thanks again for the help.

DC

 

[wyliesdiesels]

Perfect response. Thank you. I was hoping you would chime in. I've appreciated your advice in the past.

To clarify: When the house was built, the original oven was 240V only. When my friends bought the house, they replaced the original oven and that replacement oven had 4 wires. Whoever connected that oven simply used the existing house wiring by connecting the oven's neutral and ground wires together and to the bare copper ground from the wall. Fast forward many years and they are replacing the oven with a double oven.

Since my last post, I've learned the new oven is rated at 7400 watts so even though that's only a shade over 30A, it means the existing circuit won't work anyway and we'll be pulling in all new wire. I hate it for them because the cost of new wire alone is going to run nearly $300 and that really wasn't in the budget.

Thanks again for the help.

DC

whoever did that didnt know what they were doing. that was NOT a code compliant install and created a dangerous potential for shock.

what is the make and model of the new oven?

 

[DC73]

whoever did that didnt know what they were doing. that was NOT a code compliant install and created a dangerous potential for shock.

what is the make and model of the new oven?

Yep.

The new oven is a Frigidaire Gallery FGET3065PFC. I've attached the installation manual. It doesn't list the 7400 watts in the manual, though. It refers you to the nameplate on the oven which shows 7.4kW at 240V.

DC

 

[wyliesdiesels]

so youll need 8/3 NM-b and a 40a breaker

 

[billconner]

agree

 

[DC73]

so youll need 8/3 NM-b and a 40a breaker

agree

That's what I came up with as well. Thanks for the confirmation. I'm pretty handy with electrical but sometimes you run into something you haven't seen before and/or instructions that are clear as mud so it's nice to have a resource like GJ.

DC

 

[DC73]

@wyliesdiesels

We ran into a bit of a snag. Installed a 40 amp receptacle and wired the oven with a 40 amp range cord. And then we discovered the cabinet maker missed the cabinet depth by a bit.

The new 40 amp outlet extends beyond the outlet cover plate by 1/2" or so. We need to gain 1/4" and all will be well.

Is there anyone who manufacturers a 40 amp outlet for an oven in which the face of the outlet is no more than 1/4" past the cover plate (flush would be ideal)?

Thanks again,

DC

 

[wyliesdiesels]

@wyliesdiesels

We ran into a bit of a snag. Installed a 40 amp receptacle and wired the oven with a 40 amp range cord. And then we discovered the cabinet maker missed the cabinet depth by a bit.

The new 40 amp outlet extends beyond the outlet cover plate by 1/2" or so. We need to gain 1/4" and all will be well.

Is there anyone who manufacturers a 40 amp outlet for an oven in which the face of the outlet is no more than 1/4" past the cover plate (flush would be ideal)?

Thanks again,

DC

where did you find a nema 14-40? (Hint: they dont exist)

 

[DC73]

where did you find a nema 14-40? (Hint: they dont exist)

Yeah, it was a 50 amp receptacle. I didn't buy it and it was already out of the package when I installed it. Just called it 40 because that's the overall rating of the circuit. Doesn't matter and that wasn't the point of the post.

Is there a solution to the problem that involves an outlet in which the face doesn't protrude as far past the cover plate?

DC

 

[wyliesdiesels]

im not picturing what the issue is. so the outlet is pushing into the cabinet or? do you have a pic?

 

[DC73]

im not picturing what the issue is. so the outlet is pushing into the cabinet or? do you have a pic?

No pic - we didn't have time. For whatever reason, the cabinet maker recessed the back panel of the cabinet away from the wall to where there was a 3/4" air space between the back panel and the drywall. We originally mounted the old work box in the back of the cabinet. But after installing the outlet and the cover plate, we discovered the face of the outlet protrudes through the cover plate by 1/2". Had it been flush with the cover plate like a 120V duplex outlet we would have had more than enough room to plug in the cord and slide the oven into place. As it was, we were 1/4" from getting the oven to slide all the way into place because the back of the oven was hitting the back of the plug.

I couldn't find another outlet that would not stick out past the cover plate. I ended up making a small wooden recess in the back of the cabinet which let us move the entire outlet/box assembly rearward such that the face of the outlet was now flush with the inside back of the cabinet. That gained us 1/2" plus the thickness of the cover plate. Not sure I'll be there when they install the oven for the final time but all should be good now.

Voltage checked out at 124/248 and I'm happy with the way the wiring turned out even though it was a major pain. Very glad their son-in-law was willing and able to be the man in the attic.

Thanks again for your help.

DC