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.

[Bruce King]

Many of the old ranges had 120v devices such as a clock or timer. The third wire was a neutral and used also as a ground for the frame. Even when the 3rd wire was bare it was a dual purpose neutral/ground. The 3 wire plus ground cables were either non existent, rare or expensive because they were not used for sub panels for years when they should be. It made a sticky situation for home sellers when they learned their house was wired incorrectly when built. This whole thread is full of mistakes but this article explains it best.
https://www.jadelearning.com/blog/3-wire-cords-on-modern-4-wire-appliances/

[Rod Sheridan]

Tape up the neutral on the cord, do not connect it anything, put a couple of tie wraps on it to keep it away from anything.

Connect the Red, Black and ground to the appropriate terminals on the range...Merry Christmas.......Regards, Rod

[Stephen Tashiro]

Many of the old ranges had 120v devices such as a clock or timer. The third wire was a neutral and used also as a ground for the frame. Even when the 3rd wire was bare it was a dual purpose neutral/ground.


I left the old 3-wire cord on the range and wired the old 3-plug outlet as the link indicated, with 2 hots and a neutral.

[Ron Citerone]

https://www.jadelearning.com/blog/3-wire-cords-on-modern-4-wire-appliances/[/URL]

I agree. I replaced my old range at my cottage. The wiring was for a 3 wire hook up. The new range was wired for 4 wire with instructions to modify it for 3 wire. I decided to have the old 3 wire replaced and upgraded to 4 wire, not only to upgrade but because I wanted to get rid of the old wire and replace it with UF because we are in a flood prone area.

[Brian Elfert]

Apparently, my house originally had a three wire receptacle for the range. Some genius previous owner installed a four wire receptacle for the stove, but still only had three wires to the receptacle. I don't recall exactly how it was wired, but not all four connections were connected. I ran a new cable to the breaker panel with the proper four wires.

[Ron Citerone]

As I said before, In my case I chose to run a new 4 wire line instead of keeping with the 3 wire that was there.

I do remember that the directions said that if you were going to use a 3 wire set up you had to disconnect a link between the terminal bar and the frame of the stove. I would look at the info that came with the range or online for that model and find out.

[Bruce King]

The jumper only comes off when using a 4 wire circuit.

[Bruce King]

Wiring info in case anyone needs it.

[Ron Citerone]

The jumper only comes off when using a 4 wire circuit.

Yeah, that's it. I remember now. Thanks for setting that straight.

[Rollie Meyers]

The jumper only comes off when using a 4 wire circuit.

Thank you for posting that, people who say that the 3-wire receptacles have a grounding conductor, not a neutral, scare me, need to look at the rating of the receptacles, they are 125/250 volts, which means they are dual voltage, non-grounding devices.

[Wade Lippman]

I left the old 3-wire cord on the range and wired the old 3-plug outlet as the link indicated, with 2 hots and a neutral.

I am not sure what you did, but changing the receptacle is illegal.

[Wade Lippman]

Thank you for posting that, people who say that the 3-wire receptacles have a grounding conductor, not a neutral, scare me, need to look at the rating of the receptacles, they are 125/250 volts, which means they are dual voltage, non-grounding devices.

Technically you are right; the third wire is a neutral. But since it also grounds the frame, I don't see it matters what you call it. I thought it was amusing that the appliance cables at my old house had an "uninsulated neutral". Sure looked like a ground.

[Rollie Meyers]

Technically you are right; the third wire is a neutral. But since it also grounds the frame, I don't see it matters what you call it. I thought it was amusing that the appliance cables at my old house had an "uninsulated neutral". Sure looked like a ground.

It does matter what you call it, a grounding conductor is not a current carrying conductor, a neutral is, and it was allowed to have a uninsulated neutral conductor supply appliances as long as it originated from the service panel, and in many parts of the country, the NEC allowed the frame of cloths dryers & cooking equipment to be grounded to the neutral, not allowing a grounding conductor to be used as a neutral, SE cable is used from the PoCo point of attachment to the meter can and then to the main panel, SE cable consists of 2 insulated conductors, wrapped with uninsulated copper, or aluminum, conductors used as the neutral, it ain't a ground. SE cable has not been used for services around my part of California for better then sixty years, the NEC allows it, the PoCo, PG&E, does not.