Add Junction Box for Double Oven

Question

California house built in the 1960s. Here's the existing junction box for the ovens. Ovens are busted and needed to be replaced

Right away, I am confused:

• Red looks like 8 AWG
• Black, White look like 10 AWG
• Bare wire (ground?) looks like 12 AWG
• Jacket for the 4-wire is plastic/polymer, not metal

I'd feel more comfortable if they were all the same wire gauge. I don't really want to pull new wire from the breaker box.

This used to connect to a Double Oven that we are replacing with a Whirlpool Double Oven. Each oven is a 4-wire connection. Not a big deal, just match the colors to wire it up. However, I need to add more wire!

The whip on the ovens are too short for both to reach this box. I assume the solution is: add a junction box and wire both ovens into a single box right between the two ovens (vertically). No problem. Plenty of room.

Then a trip to the hardware store and some searching on the Internet made it complicated:

1. There's no grounding "hump" on the original junction box. Just tie the bare wire to the box with the screws for the coverplate or replace the box?
2. Use a metal box for the new junction box? or plastic?
3. I plan to run flexible conduit from the new box to the original box. Metal conduit + metal box? Ground them both with the bare wire? PVC conduit + plastic box because there's no metal conduit running back to the breaker box?
4. The Whirlpool ovens have 12 AWG. Can I run 12 AWG in the conduit?
5. The whip on the Whirlpool says connect ground with 8 AWG. Doesn't look like I have 8 AWG ground wire. Whirlpool supplies 12 AWG on their whip. What is the point of connecting a 12 AWG ground from the oven to a 8 AWG from the house?
6. I'd love to use this EZ-QUICK (modular cable assembly). However, you can either get 12/2 or 10/3. The 10/3 is a polymer coated conduit with only (x3) conductors and I need (x4) 10/3 at Home Depot. Looks like I cannot use this. Instead, I need to get bona fide 10/3 Example from Home Depot and need to remove the jacket, strip the wires, add a clamp to the box myself.

If I can resolve what boxes to use and I can use the existing wiring, I'm confident to proceed. If I need to pull new wiring from the breaker box and/or put in better grounding, I don't want to do all that myself.

Am I in over my head and I should hire somebody, or am I close enough that I can do this myself?

Answer 1

Your cable should be 8-8-8-10. If it's stranded, then it's definitely #8 because it would be solid otherwise. Solid is cheaper but forbidden above #10.

On your ground screw. It looks like somebody put a drywall screw through it. See the 2 holes right next to each other. Drywall screws are not for that, use deck screws.

I would cut the breaker, tap the conduit nut on the left side with a screwdriver, and unthread those wires out of the hole. Then rearrange screws as needed and/or just replace the box with 4x4 or 4-11/16" deep METAL box that has a bump-out for its ground screw. Or even multiple ones.

Or if you prefer, leave the cable alone and get yourself a 10-32 drill and tap set (#21 drill), and make a few more ground screw holes. Drill 3/8" into the wood so the ground screw has somewhere to go. Then you can just give each wire its own ground screw lol. Do I need to tell you not to place them on knockouts?

For splicing the #8 to the #12-10 leads from the ovens, a big enough wire nut will do that, but so will the ILSCO Mac Block Connector if you can find it. It's a mini-Polaris at a mini-price, but it is UL listed for multiple #12 wires in one port.

Metal boxes are superior at every task a box is there to do.

I would not run plastic conduit anywhere near an oven. Read the instructions carefully about wire spec. You can get longer 12/3 whips pre-made. That EZ-Quick looks like one of those, but yeah you need neutral for the oven light. I could swear I've seen 12/3 whips. It's vital that the oven light be 120V to allow people to use common incandescent bulbs and not have to go get a special 240V bulb. Obviously this logic utterly fails to consider the CFL-LED transition, since those do not work inside ovens, so you need a special bulb anyway.

Look at the oven draw, if it's <4800 watts you should be OK with #12.

A 40A circuit requires a #10 ground and no larger.

Am I in over my head and I should hire somebody, or am I close enough that I can do this myself?

With this level of attention to detail, you're definitely not over your head. You're asking all the right questions and don't seem to be overlooking anything huge.

Of course this is where I give the torque screwdriver speech. In the OO's research showed torque matters on the small stuff too, so a torque screwdriver must be used where a torque is specified.