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Wiring in 240 V for a combination microwave convection oven.

Wiring in 240 V for a combination microwave convection oven.

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Old 10-15-19, 04:13 PM
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Wiring in 240 V for a combination microwave convection oven.

I have this microwave convection oven that needs to run off 240v. The outlet thatís installed currently is a 120v with two hot and Neutral wires but they are both the same phase on a 20 amp breaker. The oven underneath is wired to 240v but on dual 30 amp breakerís. The new microwave/oven wants a 20 amp breaker per the manual.
What is the best way to hook this up? Should I just tap a new 240v off the oven using the same circuit on the 30 amp breakers? Or is it possible to just run one hot wire from that ovenís circuit in the opposite phase and use the common and hot from the 120 V 20a circuit that is already there to get 240v?
 
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Old 10-15-19, 04:19 PM
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Welcome to the forums.

The outlet that’s installed currently is a 120v with two hot and Neutral wires but they are both the same phase on a 20 amp breaker
That would sound about correct for a receptacle in the middle of a circuit. A hot and neutral in and a hot and neutral out. This will be of no use for the convection unit.

You cannot tap an additional appliance off of a dedicated circuit. That 30A circuit is dedicated to the oven only. You will need to run 12-3 for a new 240v 20A circuit.
 
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Old 10-15-19, 04:30 PM
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OK thank you very much. I shouldíve given a little bit more information. The circuit that is currently there is actually for the refrigerator, microwave and hood and has two 20 amp breakers. Maybe I can find the opposite phase on the same circuit? Attic access is very challenging so running a new circuit would be a task.
 
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Old 10-15-19, 04:55 PM
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You can't get one leg from one cable and the other leg from another cable.
Both legs, neutral if required and ground must be in the same cable jacket.
 
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Old 10-15-19, 05:09 PM
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The legs of the panel are not left and right. Could you please post a picture?
 
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Old 10-15-19, 05:30 PM
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Here are pictures of everything. Let me know if you guys have any ideas. The receptacle has two separate romex wire sheaths feeding the upper and lower outlet but they seem to be in the same phase.

https://photos.app.goo.gl/oH5DNE9M5KCPGaDo6

I think heís probably right I unfortunately will have to run a new circuit. This will definitely require licensed electrician and $$$ as this is a huge pain in the butt.



 
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Old 10-15-19, 06:02 PM
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Are you sure I cannot just change the breakers for the oven's junction box directly below the appliance to 40 amp and use the oven's circuit?

The fuse/breaker requirements in the installation manual allow for higher amp breakers to be used for dual oven models.

https://photos.app.goo.gl/oH5DNE9M5KCPGaDo6
 
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Old 10-15-19, 06:24 PM
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The refrigerator and micro hood are on a two pole breaker. One is fed from the black leg of the panel. The other is fed from the red. This is correct. You have two independent 120v circuits on the same device with the tabs broken between the screws.

They are not on the same phase as you state. The legs alternate ABABA top to bottom, not left right.

The one cable could be converted to a 240v circuit with some changes. It cannot serve a 120/240 circuit.
 

Last edited by pcboss; 10-16-19 at 04:03 AM.
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Old 10-15-19, 06:29 PM
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If correct you are awesome and how would I go about doing this? When I put my multimeter on the hot lead on both outlets I get 0v so that is why I thought they would be the same phase.
 
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Old 10-15-19, 06:36 PM
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I added photos with flash showing the connections. It looks like the tabs are connected.

https://photos.app.goo.gl/oH5DNE9M5KCPGaDo6
 
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Old 10-15-19, 09:18 PM
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The receptacle you show has two white and two black wires. It is AFTER the three wire MWBC split. You would need to locate the receptacle where both red and black wires are present.... however.... if you do that.... you lose all those 120v receptacles so that wouldn't be terribly effective.

Every appliance has a maximum over current protection rating. An oven circuited at 30A can not be connected to a 40A circuit. You cannot just install a larger breaker on a circuit. The circuit must be protected based on the size of the wiring.
 
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Old 10-15-19, 11:16 PM
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You were correct from the beginning. Thank you for your help Iím just gonna have to have an electrician crawl through my attic and run a new circuit. It will be a challenge.
 
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