Hard wiring a 4-wire oven to 3-wire outlet?

Question

I am replacing an old 4-wire oven with a new Kitchen Aid 4-wire oven. I have 3 wires in the outlet box (black, white, bare (ground)). The old oven was connected the following way: From the oven the white wire and the bare (ground) together were connected to the bare (ground) in the box. The black wire from the oven was connected to the white wire in the box and the red wire from the oven was connected to the black wire. There was a lot of black electrical tape wrapped around the white wire in box about 3 inches from the connection point. Not sure what that means? I was planning to connect the same way, but see some instruction on the internet to connect the same way, except black goes to black and white goes to red. Confusing and conflicting information and not sure which is correct way. Or does it not matter since each wire, black and the white are hot each supplying 110V for a total 220V?

Answer 1

Sounds like a problem, but need more info

It sounds like you had an improper hot => hot, hot => white-normally-neutral-used-as-hot and neutral+ground => ground. If that's what you actually have, then it is a messed up version of the older style (not normally allowed now, but grandfathered in for some situations if done correctly) hot/hot/neutral connection, but using a 2-wire + ground cable instead of a 3-wire cable.

If I am correct, that means:

• Ground is carrying the neutral load for the 120V controls. Ground is not supposed to carry any load except under fault conditions.
• Wire colors are non-standard. White is supposed to be neutral, not hot.

I am also concerned that if someone cheated on the type of cable, they may also have cheated on the size of the wires. The actual wire gauge that you need will depend on the circuit - 30A vs. 40A vs. 50A., but the typical ordinary 2-wire + ground cable is often 12 gauge for 20A or 14 gauge for 15A and definitely not safe for 30A or more.

Before doing anything else, you need to find out the actual circuit requirements for the new oven. Check the oven manual - and post the model # here so we can take a look too. Then check the breaker or fuse to see if it meets those requirements. It needs to be big enough - to avoid nuisance trips - but not any bigger than it is supposed to be, so that it can provide the proper protection.

Whether or not the breaker is correct, I have a feeling you will need a new 4-wire (hot/hot/neutral/ground) cable to replace the existing cable. There is a possibility that a 3-wire connection (hot/hot/ground) may be OK, but we can't tell without more information.

If the existing 3-wire cable (2 insulated wires + ground) is sufficient, then the question is whether it is thick enough. You can check a wire chart, but the key numbers are typically:

• 15A - 14 gauge
• 20A - 12 gauge
• 30A - 10 gauge
• 40A - 8 gauge
• 50A - 6 gauge

There should be markings on the existing cable, or measure the wire directly.

Using a high-current breaker with wire that is not rated for that current is against code and DANGEROUS.

Answer 2

I'm sure they had a 3 wire circuit where they needed 4 so they jumped the neutral from the oven to the ground so your white from wall is hot the black is hot and the white from oven jumps to ground