New 4 Wire Range to 3 Wire Receptacle

Question

I currently have a 3 wire, 40 amp circuit for my range. Home was built in '78. I bought a new ZLine dual fuel range which came with a 4 prong cord installed. The instructions do not cover converting for 3 prong use. I have not removed the range cord panel as yet but am trying to figure out what makes the most sense.

I can run a ground to my panel from my receptacle box but it seems silly since my panel bus has all neutrals and grounds going to the same location. Should I simply jumper the ground and neutral in the range and call it good?

I can't imagine manufacturers selling a range for $5K then letting you know you need $2K of new wiring installed. Am I missing an obvious solution?

As you can see there is no separate ground in the box.

I guess I should have said that I hunted around quite a bit before posting here so I am aware of the easy fix if there was but in this case there is no separate ground, the box is phenolic and this is the original wiring.

Please ignore the white tape on the other leg, I added it. This is why I was asking about running an individual ground wire back to my panel as the bare neutral is already going to the same bus in the panel. I want to do this correctly but not sure of the best approach.

Answer 1

This is basically a rule that changed 50+ years ago and is still being grandfathered. The fact that your new range does not give instructions on converting to 3-prong use is a good thing. An end to the madness.

Here is what is going on:

Grounding of branch circuits is a relatively new thing. But it has been around at this point for decades. Due to industry pressure (there are reasons, there is some logic, but by now we should be long past it), 3-prong receptacles for dryers and ovens/ranges still exist. They have 2 hots and neutral and no ground. 4-prong has been around for a long time, and it is extremely likely that your existing circuit already has the ground wire available.

The problem is that under certain unusual, but not impossible and not actually that rare, situations, a broken wire, bad receptacle, etc. can result in a 3-prong circuit going bad in a way that the metal case of the appliance is "hot". That kills people. On 120V circuits in the most dangerous places (any place with water, so starting with kitchen and bathroom) there has been an effective solution using GFCI. But GFCI only recently became available for typical 240V circuits such as dryers and ovens/ranges, and is still relatively expensive. Proper grounding doesn't solve every problem that can go wrong with these circuits, but it does solve a lot of them.

So if a 1978 home likely already had ground, why do you have a 3-prong receptacle? Simple. Inertia.

• First range - 4-wire to match the new house
• Replacement range - appliance company brings it with a still-common 3-wire plug. Instead of swapping the plug/cord (trivial) they swapped the receptacle. Hopefully they left that ground wire sitting inside the receptacle and didn't chop it off.
• Now you get a 4-wire range and instead of switching the receptacle back, you want to change the plug/cord to match the receptacle. Because that's easier.

But easier isn't always the right thing. In this case it is absolutely the wrong thing.

I have to admit that the whole neutral/ground bond thing still confuses me a bit as to exactly how/why it sometimes causes problems if you have multiple bonds. But that's what happens and code has recognized that for decades.

Fix it once and for all

• Open up the existing receptacle. You will likely find one of four possibilities:

  • Cable - Black/Red/White/Bare-or-green cable - you already have ground (bare or green) so install a 4-prong receptacle and you're done
  • Cable - Black/Red/White - you don't have ground. But you have admitted you can run a separate ground, and that is allowed (it hasn't always been allowed) so run that ground and install a 4-prong receptacle and you're done
  • Cable - Black/White/Bare - this is a bit of a problem. In ye olden times there could be bare neutral. There still can be in feeders. The problem is you need to make sure the bare wire is only neutral and doesn't touch any metal case or other stuff that would effectively make it ground. And then you would still need to add a separate ground wire, as you can't just make this ground and add a white neutral (because all wires except ground must be in the same cable). If you actually find this, post pictures. I'd be surprised to find this in a 1978 house.
  • Conduit with individual wires - this is super easy. If it is metal conduit then that will likely work as ground (depends on type of conduit). Whether it is metal or not, you can add a ground wire inside the conduit, which is generally easier than routing one separately through the house. But again, it is likely you already have the ground wire in the conduit.

Basically you have no excuse not to bring this up to modern code. It is safer that way. Just do it. And it may turn out to be super easy using the wires that are already there and just changing the receptacle.

As for:

I can't imagine manufacturers selling a range for $5K then letting you know you need $2K of new wiring installed.

That's really not the case here, provided you already have a 40A circuit with appropriately sized wires. But it certainly happens that someone only has a 30A circuit and needs to run new wires/cable. I had that with my Kitchenaid Double Oven 20+ years ago. My electrician was complaining how much the cable cost (even though he passed the cost on to me) and that cable really wasn't hard to run at all, compared to what some people have to go through. But $2K? That sounds a bit extreme, unless you end up needing a heavy-up (panel replacement) to add the 40A circuit.

Answer 2

I replaced the circuit with new copper 8/3 with ground wire. Installed the appropriate 4 prong receptacle in a new metal box that allows me to rotate the plug horizontally for easy plug in. Was difficult but now it's correct.