Putting a 4 wire power cord on an old electric range

[Stephen Tashiro]

To adapt an old electric range so it can be plugged into a modern 4-plug receptacle, I'd like to put a modern 4 wire power cord on the range. What's the effect of connecting the ground on the new power cord to the chassis of the range?

Do old ranges isolate the neutral wire from the chassis? If they connect the neutral wire to the chassis inside the range, then the ground on the new cord would effectively connect neutral to ground. Is that ok?

[Mike Henderson]

I can't answer your question "for sure" but I really doubt if it would be allowed to attach the neutral to the frame of the stove. You don't say how old the stove is but UL has been around a long time and I really doubt if UL would allow neutral to be connected to the frame.

Mike

[Stephen Tashiro]

You don't say how old the stove is but UL has been around a long time and I really doubt if UL would allow neutral to be connected to the frame.

Mike

I'll check with a meter.

[David Bassett]

How is the old stove wired? You imply it is 3-wire and that suggests it is two hots & a ground, i.e. doesn't use the neutral lead (so no 120V for accessories.)

If that's the case all you need to do is wire 3 of the four wires, (or 3 of the four plug pins,) and leave the fourth unconnected. (Cap the fourth wire or leave it open in the plug.)

[Paul F Franklin]

Unfortunately, on older ranges with three wire cords, neutral was indeed often connected to the chassis. Evidently back then this was considered acceptable risk given the heavy gauge connections and infrequent plug/unplug cycles. These days of course it is not allowed and 4 wire cords are required. Normally the connection to the chassis is generally a single point connection near where the cord enters the appliance. It's usually straightforward to un-bond the neutral from the frame and tie it only to the white wire in the cord. Then the green wire must be attached to frame.

[eta:] Of course you need a four wire feed to the range to be able to do this.

[Frank Pratt]

I can't understand how the decision to allow grounding via the neural, or the other way around, was even arrived at. Makes no sense. Why even bother having separate & isolated (after the service) neural & ground wires if they were going to allow dumb exceptions like that.

[Paul F Franklin]

I can't understand how the decision to allow grounding via the neural, or the other way around, was even arrived at. Makes no sense. Why even bother having separate & isolated (after the service) neural & ground wires if they were going to allow dumb exceptions like that.

There are several (admittedly rare) situations that cause safety issues if neutral and ground are bonded anywhere other that at the service entrance. But that was not the situation with 3 wire range service...there was no ground, only the neutral. Even on a range service, the neutral will be very nearly at ground potential because there is little current flowing in the neutral, only that from the few 120 volts loads in the range...lights, maybe a little control current, but that's it. If the neutral were to be broken or disconnected, there would be a shock hazard from touching the range, which is why four wire circuits are now required. But the situation where the neutral was open was (I assume) judged to be less of an issue than leaving the range frame floating and risking that a short inside the range would energize the entire range with no indication (tripped breaker) that there was such a fault. Codes are always compromises, is the benefit gained worth the cost to comply.

[Bill Dufour]

My house was built in 1949 and it has a ground rod that neutral is connected to. There is no ground wire outside the main panel. It is two hots and a neutral. In the late 1960's washers had a bare ground wire that was attached to the water faucet. I think they had a three wire cord by then and the extra wire was only attached if the outlet was not grounded.
Bil lD.

[Stephen Tashiro]

How is the old stove wired? You imply it is 3-wire and that suggests it is two hots & a ground, i.e. doesn't use the neutral lead (so no 120V for accessories.)

If that's the case all you need to do is wire 3 of the four wires, (or 3 of the four plug pins,) and leave the fourth unconnected. (Cap the fourth wire or leave it open in the plug.)

Update: Yes, that's the situation. The stove cord and (old) outlet are wired with two hots and a ground. No neutral is connected.
Kenmore model 9119278410

[David Bassett]

Update: Yes, that's the situation. The stove cord and (old) outlet are wired with two hots and a ground. No neutral is connected.
Kenmore model 9119278410

If there's a clock or timer or any accessory, double check. Paul Franklin's wiring description makes sense and if it's your case you can implement a safety upgrade by wiring all four wires:

Unfortunately, on older ranges with three wire cords, neutral was indeed often connected to the chassis. Evidently back then this was considered acceptable risk given the heavy gauge connections and infrequent plug/unplug cycles. These days of course it is not allowed and 4 wire cords are required. Normally the connection to the chassis is generally a single point connection near where the cord enters the appliance. It's usually straightforward to un-bond the neutral from the frame and tie it only to the white wire in the cord. Then the green wire must be attached to frame.

[eta:] Of course you need a four wire feed to the range to be able to do this.

[Bruce King]

To find out, need a current clamp, check each hot leg for small amount of current with the cooking elements all turned off. If current is present and different on either leg there is a clock or electronic control module present that is using 120v and needs the white wire from that device jumpered to the incoming white wire if you have a 4 wire circuit. Don’t jumper to a white wire being used as a hot on a 3 wire circuit. Wrap black tape on any white wire being used as hot.

[Stephen Tashiro]

Unfortunately, on older ranges with three wire cords, neutral was indeed often connected to the chassis. Evidently back then this was considered acceptable risk given the heavy gauge connections and infrequent plug/unplug cycles.

I can't determine how the wires to the old 3-plug outlet were attached to the breaker box because the most of the old wiring is missing. At the outlet, I see that the end of the old wiring is 3 stranded copper wires, one black wire, one red wire and one bare wire.

The range does have a clock. A meter shows there is continuity between the chassis and terminal on the range that is connected (via the power cord) to the bare wire.

[David Bassett]

I can't determine how the wires to the old 3-plug outlet were attached to the breaker box because the most of the old wiring is missing. At the outlet, I see that the end of the old wiring is 3 stranded copper wires, one black wire, one red wire and one bare wire.

The range does have a clock. A meter shows there is continuity between the chassis and terminal on the range that is connected (via the power cord) to the bare wire.

How much rewiring are you up for?

Can you add a (white) wire directly from the clock to the white in the 4 wire cord? If so, you can then wire red to red, black to black, and green (or bare) to the chassis. It sounds to me like that'd update your range to modern standards.

[Stephen Tashiro]

How much rewiring are you up for?

Can you add a (white) wire directly from the clock to the white in the 4 wire cord? If so, you can then wire red to red, black to black, and green (or bare) to the chassis. It sounds to me like that'd update your range to modern standards.

I'm not up to revising the internal wiring of the old range. From looking at internet videos, apparently many modern ranges provide a way to separate the neutral connection from the ground by disconnecting a "grounding strap" between two terminals. This old range doesn't make things that simple. I"m not living at the house, so it isn't critical to put the old range back in service.

My conclusion is that the standard wiring for 3-plug outlets (in the late 60's and later) was to have two hot wires and a neutral. I don't understand why the third wire in the old cable is a bare wire instead of a white wire, but I can tell that the old cable is for an even older (1950's vintage) range. I think the old 3-plug outlet is not the original outlet installed when the house was built.

[Ken Combs]

I'm not up to revising the internal wiring of the old range. From looking at internet videos, apparently many modern ranges provide a way to separate the neutral connection from the ground by disconnecting a "grounding strap" between two terminals. This old range doesn't make things that simple. I"m not living at the house, so it isn't critical to put the old range back in service.

My conclusion is that the standard wiring for 3-plug outlets (in the late 60's and later) was to have two hot wires and a neutral. I don't understand why the third wire in the old cable is a bare wire instead of a white wire, but I can tell that the old cable is for an even older (1950's vintage) range. I think the old 3-plug outlet is not the original outlet installed when the house was built.

In the 3 wire range configuration of the 60s, there is/was no neutral. the bare wire is a ground, not neutral and is not intended to carry current except in a fault situation. The risk is when/if a leak, hot to ground develops that is not of sufficient magnitude to trip the breaker. In that case the appliance from has voltage potential and could shock a user that touches it and is grounded in some way.