Cooktop - 2 wire to 220v 3 wire

14 years ago

I'm trying to connect my GE Induction cooktop but find the instructions confusing. The cooktop has 2 wires - red & black plus a green ground. The house circuit has 3 wires black, red, white & bare ground. Anyone have experience on how to properly connect the 3 house wires to the 2 cooktop wires?

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pharkus

14 years ago

I've been wondering why they didn't do this a long, long time ago.

We've got a lot of older grandfathered 3-wire installations, but code now wants 4-wire receptacles, with ground/neutral seperate.

Alright, fine, but I always wondered: Why do we have 120/240 appliances anyway? Clothes dryers tend to have a 120V motor, but I can see no reason not to use a 240V motor instead. I can't see anything in a typical range that uses 120, with the possible exception of some of the electronic controls on modern ovens, which are low-voltage internally anyway, so if you're gonna use a 120-to-whatever transformer, why not a 240-to-whatever one?

It would seem, to me, a lot simpler a solution!

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Comments (11)

mike_kaiser_gw
14 years ago
Red to red, black to black (although it really doesn't matter if you reverse them), and green to the bare ground. Cap the white with a wire nut and fold it back in the box, it's not needed in this situation. The cooktop is straight 240v while the house wiring can accommodate a 240/120 appliance.

I'm assuming the circuit you're connecting to is appropriately sized for the cooktop.
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That confused you all? I would sincerely hope it did not confuse your electrician. Your new oven draws 3600 watts at FULL load @ 120/240v. A watt is a watt. At that point amperage is determined by the voltage. At full load this is a nominal 15 amps. This is NOT a 15 amp circuit. Why did you call Lowes about this? All they did was sell you the thing. They are most often clueless about these matters and often give anywhere from erroneous to downright dangerous advice. Unless the instructions SPECIFICALLY state so, all you need is a 120/240v-20 amp circuit for this appliance. Since this unit requires 120 & 240 volts you must run a 4-wire cable in the XX/3 variety. Such as 12/3 (with ground) NM cable. IF the unit required a 30 amp circuit then 10/3 would have been appropriate. "And finally why is it called 220v if it's really 240v? Who calls it 220v? Not me. That is a generic term adopted by the masses. Actually your oven is 120/240v, NOT simply 240v. There IS a difference.
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If the hot touches either the white (groundED) conductor or the green/bare (groundING) conductor a short will be created and the breaker (or fuse) will open the circuit. The white wire carries the return current from the black wire, and WILL develop a small voltage caused by the resistance of the wire itself. If the appliance frame was connected to this wire, it would have this voltage present. If the white wire connection became open, the frame would rise to a full 120 V. For these reasons the groundING (AKA 'safety ground') was added. It NEVER carries current except when a fault occurs. This means the equipment frame stays at a very solid ZERO volts. Since most portable lamps do not have a ground connection (2 prong plugs) one blade of the fixture connection is made larger. This is called a 'polarized' plug. It ensures that the screw shell of the lamp is on the white conductor and not connected to the 120 V hot side. It is much easier to come i contact with the screw shell of the bulb socket that the hot side. The hot side is all the way at the bottom of the screw i socket, while the shell is relatively exposed.
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Ron Natalie
14 years ago
Cooktops I don't know about, but ranges and wall ovens typically have a 120V lightbulb inside (and some older ones had 120V convenience receptacles as well).
petey_racer
14 years ago
"We've got a lot of older grandfathered 3-wire installations, but code now wants 4-wire receptacles, with ground/neutral seperate. "

This only applies to 120/240v appliances. The OP has a straight 240v appliance. The neutral is not needed but a ground is.
User
Original Author
14 years ago
Mike - thanks for the confirmation. That's what I thought was meant but I feel better with some validation. Appreciate the response.
brickeyee
14 years ago
"Cooktops I don't know about, but ranges and wall ovens typically have a 120V lightbulb inside (and some older ones had 120V convenience receptacles as well)."

The manufacturers (probably at UL prodding) finally did away with the 'convenience receptacles' during the 1970s.
The stove did not have any secondary overload protection, meaning there was a 30-50 amp breaker feeding that receptacle.
ksvalentine
14 years ago
The oven I want to buy is a 120/240v wall oven, and the spec says 20A circuit. If it's a 3wire connection, would a 10/3 wire cause damage when used in a 2-pole 20 breaker?

My cooktop is a 120/240v surface mount, 40A and it has only two wires (black/red) and a bonding ground. Wouldn't that make it an 8/2 conductor for this circuit?

About the oven then, if the oven has (I don't know yet) the same wiring (red/black/gnd), then could a 10/2 be used if it's a 20A circuit?

I hope this response goes to my email. ;)
petey_racer
14 years ago
ksvalentine, it would have been better to start a new thread for your questions instead of adding them to this existing and still active thread.

The responses will not go to your e-mail. I don;t think this site offers this function. I hope you come back to check.

Both your new appliances will need FOUR wires. Two hots, a white neutral and a green or bare ground. If the appliance only has a black and red it will be a 240v appliance, not a 120/240v appliance.
ksvalentine
14 years ago
peter racer-

Thanx, this is my first time on this blog. I posted a new thread.
fa_f3_20
14 years ago
"The oven I want to buy is a 120/240v wall oven, and the spec says 20A circuit. If it's a 3wire connection, would a 10/3 wire cause damage when used in a 2-pole 20 breaker? "

No, 10 ga. is fine. A 20A is allowed to be as small as 12 ga. (provided that it doesn't have to be derated for some reason). You can always under-breaker a circuit, as long as whatever is feeding the circuit will run without tripping.
pharkus
14 years ago
The manufacturers (probably at UL prodding) finally did away with the 'convenience receptacles' during the 1970s.
The stove did not have any secondary overload protection, meaning there was a 30-50 amp breaker feeding that receptacle.

I've seen at least one with one of those pushbutton thermal breakers (like you find in the back of old TVs) for the receptacle.

Cooktop - 2 wire to 220v 3 wire

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Cooktop - 2 wire to 220v 3 wire

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