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Replacing Electric Range and Micro with Cooktop and Combo Wall Oven

Replacing Electric Range and Micro with Cooktop and Combo Wall Oven

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Old 04-16-15, 12:33 PM
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Replacing Electric Range and Micro with Cooktop and Combo Wall Oven

Hello...upgrading kitchen cooking appliances from a single electric range with a Microwave above(both are plug in) to a glass cooktop and separate wall oven/microwave combo oven. They will be located on the same wall in the kitchen, about 18 inches apart.

The combo oven is one appliance that consists of 2 components--the microwave is bolted onto the oven with machine screws. The micro component has a regular 3-prong plug, which plugs into a receptacle in the back of the oven component. They have separate control panels, and my hunch is they could be separated and installed independently.

The condo was built in 2002. There are 2-45 amp single pole (tied) breakers feeding the existing range, and the existing wire on the circuit is 6-3 with ground(4-wire) stranded Romex. The old microwave was on a dedicated 20 amp circuit on 12-2.

No more space in my panel to add another 40 amp circuit, so I'd like to run the cooktop and combo oven on the same 45 amp circuit. Nothing in the manufacturers' installation instructions preclude this.

The nameplate rating on the cooktop is 7200w; 6600w on the combo oven. I've done a bit of research and it seems the NEC has special considerations for allowing multiple cooking appliances on the same circuit. When I apply the math it seems I have adequate ampacity to run both on the same circuit:

7200w + 6600w = 13,800 / 240 = 58 amps x .65 demand factor = 37 amps

An alternative table allowing me to treat these as a single range yields a higher ampacity of 43. This calc is a bit more complicated, so hopefully I did it correctly.

Assuming above math is correct, is there any reason I can't proceed?

My plan is to connect both appliances to the incoming 6-3 plus ground in the same metal junction box to be located in the base cabinet between the 2 appliances. Oven is 4-wire, cooktop is 3 wire. Is it as simple as wire-nutting all like-colors together with a pigtail to a grounding screw on metal jbox?

Never worked with 240 before--all feedback appreciated.

Thank you,
Trish
 
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Old 04-16-15, 12:49 PM
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It sounds like a reasonable approach. 6-3 NM is actually capable of supporting 55A if you need to increase the breaker to support both appliances (doubtful). I really don't see a problem. Are the oven and stove cord-and-plug connected or hardwired? You may be required to connect each appliance in the space directly behind/under it, which would require an additional junction box and a few feet of 6-3.

If by "3-wire" on the cooktop, you mean 240V only then it will not have a white wire. The hots and ground would connect to the branch circuit.

You may need to get some insulated screw connectors to make the splices. I don't know any wirenuts off the top of my head that will take a #6 plus two #10 (or more?), or two #6 plus a #10.
 
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Old 04-16-15, 01:03 PM
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The Oven/Micro Combo is hardwired--4-wire metallic whip; The cooktop is also hardwired, 240 only--2 hots and a ground. If cooktop installed in its own jbox, would I simply cap the incoming (unused) neutral?

Was hoping to avoid having to connect 2 6-3s in the same j-box--sounds like I need to find some x-large wire nuts.

Thank you, Tish
 
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Old 04-16-15, 01:55 PM
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If cooktop installed in its own jbox, would I simply cap the incoming (unused) neutral?
Yes.
sounds like I need to find some x-large wire nuts.
How large is the box? Ideal 454 Blue lists 2 #6 + one *12. How large is the box?
 

Last edited by ray2047; 04-16-15 at 03:10 PM. Reason: Clarify my comment.
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Old 04-16-15, 02:23 PM
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Haven't purchased the boxes yet. Ideal 454 would work, assuming the wires on the metallic whip are 12 or smaller, correct?
 
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Old 04-16-15, 06:06 PM
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An earlier reply stated I may have to have separate junction boxes for the oven and for the cooktop. Could someone expand on why that is? I can't seem to find any code info specific to this point.

Ideally I'd like to locate a single j-box in a base cabinet between the wall oven and the cooktop. I am reasonably certain the whips are long enough to allow me to do this, as the 2 appliances are only separated by an 18 inch base cabinet.

Assuming I have an adequately sized box for the number of conductors, what other factors are at play here.

It's not a show stopper either way, but it would make life a bit easier if I could bring the 6/3 wire into a single jbox and make the connections to both appliances there.

Thank you...Trish
 
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Old 04-16-15, 06:07 PM
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Since you have never worked with these large gauge wires, just a few tips.

- Get a metal box as large as possible, use extension box if needed. Ensure it has the proper knock out sizes, 1/2"
- Purchase Two 1/2" flex connectors, either angled or straight

When connecting whips to house wiring:

- The factory strips the whip wiring rather short. Carefully strip the whip wiring a little longer (both cook top and oven) and pre-twist the two together before connecting to house wiring. Whip wires should be stripped a little longer than house wiring.

- I'm usually not a pre-twister, but you must be careful with stranded wires.
 
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Old 04-16-15, 06:40 PM
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Thank you Handyone...appreciate the tips. Can I assume from your reply you see no issues with me making all connections in a single j-box inside of an adjacent cabinet?

Thanks, Trish
 
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Old 04-16-15, 07:29 PM
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So long as box fill isn't exceeded you are okay but larger than minimum is easier. Electrical Box Fill Calculations - Construction Monkey
 
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Old 04-16-15, 09:24 PM
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Ray addressed the box fill issue and you will be OK with a single box, bigger the better.
My precautions are for a secure connection. Anytime you connect two or more stranded wires to a larger stranded wire or larger solid wire, you can run into trouble.

Follow my advice on strip length. After making connection, hold wire nut with one hand and tug on smaller wires with other hand to ensure the smaller wires are snug and won't pull out.
 
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Old 04-16-15, 10:00 PM
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Though not mentioned with stranded wire I twist the strands to gether before twisting it to another wire. Not sure if needed, just the way I learned,..
 
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Old 04-17-15, 03:45 AM
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Thank you, everyone, for your suggestions and input.
 
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Old 04-17-15, 06:32 AM
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An earlier reply stated I may have to have separate junction boxes for the oven and for the cooktop. Could someone expand on why that is? I can't seem to find any code info specific to this point.
It's a common point of contention regarding what is "accessible" when working with your local inspector. Some believe that if you have to move a different appliance in order to disconnect this one, it does not meet the accessible standard. It's something you could run into, but might be able to clear up in advance by talking to the inspector when you get the permit.
 
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Old 04-17-15, 06:47 AM
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If I install in a common j-box located in the base cabinet between the oven and the cooktop, I would not need to move either appliance to get to the j-box. It will be always accessible.
 
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