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#38703 - 05/30/04 06:05 PM Is my electrician being unsafe?  
dkershner  Offline
Junior Member
Joined: May 2004
Posts: 2
Austin, TX, USA
I am not an electrician, but I am concerned about the safety of a job that an electrician has proposed for my kitchen. I am installing a 30 inch wall oven where a microwave used to be. The oven power rating is for 240V, 20 amps. Because of the layout of my house, it is very difficult to run a new electrical line from the sub panel to the kitchen. Therefore, the electrician is proposing to use the existing wires from a 120V/20amp wall outlet (that was dedicated for my microwave) to create a 240V junction box by rewiring the neutral line as a second hot line, and using the ground as the neutral line. He told me that the existing wiring is already rated for 20 amps, so this should be no problem. He said he just needs to install a double pole breaker switch in the sub panel where each is rated for 20 amps. I think my main concern is with the size of the wires being used - these are thinner wires from a regular wall outlet. I was under the impression that a job such as this required the much thicker wires that I've seen in other 240V junction boxes.

Is this safe? Thanks.


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#38704 - 05/30/04 06:16 PM Re: Is my electrician being unsafe?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
This will be hard to pin down with out pictures.

If
Quote
The oven power rating is for 240V, 20 amps


is correct than there is no need for a neutral and 12/2 cable used to feed kitchen outlets will be fine.

If the ovens rating is more than 20 amps the wire will be too small.

If the oven is rated 240/120 20 amps it will need a neutral along with 2 'hots'

Using the grounding conductor for neutral is not an option.

If you need 240/120 you will need to run a new wire.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#38705 - 05/30/04 06:20 PM Re: Is my electrician being unsafe?  
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
N.C.
Using the white wire for a "Hot" wire in a cable assembly is perfectly fine and a normal installation.

The problem is using the bare conductor of the assembly for a neutral conductor.

If the unit does need a neutral there is no way out of running a new 12/3 with ground.

Roger


#38706 - 05/30/04 06:21 PM Re: Is my electrician being unsafe?  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
Bergen County, NJ
The size of the wires would be dictated by the current, not the voltage. The same wire size (12 AWG) that is acceptable for 20 A at 120 V would work be acceptable for 20A at 240V.

Remarking the existing neutral and using it as a hot wire is acceptable, as well (if done in a manner consistant with the code). Where the plan sounds questionable is the reusing of an existing ground wire as a neutral. The ground wire is most likely a bare conductor, and cannot be used for anything other than a ground. If reused as a neutral, then there will also be no ground wire to the new oven. The oven MUST be grounded.

It is possible that the new oven does not require a neutral, in which case the installation would be OK as described, except that the existing ground wire would remain as a ground, not a neutral. The manual for the oven will tell what kind of wiring is required.


#38707 - 05/30/04 06:22 PM Re: Is my electrician being unsafe?  
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
N.C.
Hello Bob, I guess I started typing as you were posting. [Linked Image]

Roger


#38708 - 05/30/04 07:07 PM Re: Is my electrician being unsafe?  
dkershner  Offline
Junior Member
Joined: May 2004
Posts: 2
Austin, TX, USA
I looked at the connection again, and noticed that the ground is not insulated, so I can't use it as a neutral.

Here's another scenario my electrician presented:

I'm actually installing 2 ovens, and he said we could connect both of my wall ovens to one junction box instead of using the wiring from the microwave. There is already a juntion box in place for the lower oven. The lower oven is rated 240V 20 amp and the upper is rated 240V 30 amp. Is it safe to connect both ovens to one box and use a 50 amp double pole breaker? The breaker in the sub-panel appears to be rated for 50 amps for this box, and the wiring in the junction box is very thick (It was used on the old oven that I recently removed - it's definitely not the same type of wiring that was in the 120V outlet).

Is this safe? Thanks.


#38709 - 05/30/04 07:21 PM Re: Is my electrician being unsafe?  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
Bergen County, NJ
No, that isn't an acceptable installation either.

In that situation, the wires feeding the individual ovens (and the ovens themselves) would not have effective overcurrent protection. The wires (and ovens) would be rated for only 20A or 30A, but would be "protected" by a 50A breaker. The wiring could easily become hot enough to start a fire before the 50A breaker tripped out.

The only way I can see to safely reuse the existing 50A range circuit would be to use it to feed a small subpanel, which would house separate 20A and 30A 2-pole breakers to protect the individual ovens. Then you need to have a location suitable for installing the subpanel, as well.

[This message has been edited by NJwirenut (edited 05-30-2004).]


#38710 - 05/30/04 07:34 PM Re: Is my electrician being unsafe?  
Bomzin  Offline
Member
Joined: Mar 2004
Posts: 28
Utah
Current code dictates all new installations will be 4 wire for ranges and dryers. Also does the oven run at 20 amps if so it will require a 30 amp feed. Look at amps on the id tag. Breaker will have to be atleast 120% of the given value.

Neil


#38711 - 05/30/04 07:59 PM Re: Is my electrician being unsafe?  
scameron81  Offline
Member
Joined: Feb 2004
Posts: 75
Healdsburg, ca, USA
Tapping the existing 50A circuit to run both ovens is an acceptable method of wiring per
210.19(A)(3) exception number 1, as long as it meets these requirements.

1. amapacity of taps are at least 20A

2. The taps are not longer than necessary to service or permit acess to the junction box

3.The junction box is adjacent to each unit.

4. The taps are properly spliced

5. The taps are of sufficient size for the load to be served.


#38712 - 05/30/04 08:04 PM Re: Is my electrician being unsafe?  
Electric Ian  Offline
Member
Joined: Feb 2004
Posts: 133
MA, USA
Wouldn't the range tap conductor exception allow using 20A and 30A conductors off the 50A branch circuit:
210.19(A)(3)
Exception No. 1: Tap conductors supplying electric ranges,wall-mounted electric ovens, and counter-mounted electric cooking units from a 50-ampere branch circuit shall have
an ampacity of not less than 20 and shall be suffýcient for the load to be served. The taps shall not be longer than necessary for servicing the appliance.


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