wiring a cooktop

[Chuck Stewart]

On a kitchen remodel we decided to go with an electric counter-top range. My research told me that all new range installs require a 4 wire to the location so I purchased and ran a 6-3 w/ground with a 40amp breaker in the panel. While waiting for the counter-top to be delivered I decided to unpack the range and see if it had a plug or required a direct wire. It had armored cable for a direct wire and to my amazement only had 3 wires coming out, 2 hot and a ground. So I grab the instructions and it says you can wire to a 3 or 4 wire house wiring by simply capping the white or neutral wire if you have the 4 wire like I thought was required! So that tells me it must be using the ground as the return instead of a dedicated white neutral. This bothers me because the ground is never as large as the other wires and their using this for the return? And if all new installs require 4 wire runs why would you send me a new appliance with only 3? I found some articles where they mentioned that manufactures put a jumper from the would be neutral slot in the appliance to the ground a call this sufficient. Just seems kind of shoddy to me and never heard of not having a dedicated (white) return wire. They say just hook the black to black, red to red, ground to ground and outlet box and cap the white. Does this seem perfectly acceptable to you?

[Art Mann]

Your stove is mostly operating as a 240VAC device. That means that there is no "neutral" current except for a small amount used to drive a display, timer and similar low current control features. Although these functions might also be driven directly through 240VAC, chances are the ground wire is indeed used in a small way as a current carrier.

[Chuck Stewart]

Ok, thanks Art, I was thinking there would be a continuous flow of high voltage thru the ground wire. So your saying it just draws what it needs from the circuit depending on how many burners are being used, I was thinking more like a receptacle where it's returned to the panel. Guess my understanding of current flow is a little fuzzy, it just didn't sound right to do it the way they instructed.

[Chris Padilla]

The ground wire is for safety and safety only. It allows a path for current to flow (BTW, current flows...not voltage :) ) to ground instead of through YOU to ground.

In your case, the stove is running off both poles (240 V) to get the necessary current to operate a high-powered piece of equipment like a cooktop. If it ran at 120 V (this is where your neutral comes into play as it is center-tapped between the two hot poles thus splitting the 240 V), then the current would be doubled and your wire gauge would need to increase. Running at the higher voltage allows less current to flow for the same power. Double the voltage, half the current. Half the voltage, double the current. Current is what determines the size of your wires.

In fact, the reason the power poles from the electric company run at such high voltages (10s of thousands of volts) is to keep the current low thus keeping the wire gauge low thus saving money on the wire. When those thousands of volts reach your home, they go through a step-down transformer to reduce the voltage to the 240 V that enters your home.

So unfortunately, you paid for an extra #6 wire that you didn't need but perhaps in the future you'll need 120 V at your stove/oven/cooktop. Just cap it and stuff it back in the box and no worries.

I'm curious how you wired this into your panel where the breaker resides. Is your panel the main or a sub-panel?

#6 wire is actually good for 50 A. #8 wire is good for 40 A. Did you use #6 because you had a very long (100+ feet) run?

[Chuck Stewart]

Chris, you got me to thinking what I actually did behind that wall so upon further reflection my wife wanted both a counter-top electric range and a double wall oven on the same wall. We already had an electric stove plugged into a 4 wire 40amp plug. So I told her I'd just slide the existing wire for that down to run her range and purchase new wire for the double oven. Both said they require a 40amp breaker. I disconnected the 4 wire plug that was already wired to the main panel and put it in a box for direct wire below the cooktop. It was at least a #8 but possibly #6 Then I purchased a 50' #6 for the double oven and used the entire length to reach the main panel. I remember the wife giving me that "look" when she saw the price so I asked her if she wanted a double oven or not? I knew I had to have at least a #8 but I was thinking better to go big and erase any doubt. So it was I guess overkill. It just had me nervous when I have a 4wire run and no white wire coming out of the range

[Chris Padilla]

The lights on the old stove probably needed 120 V to run. Lights that run on 240 V are kind of rare and not readily available if you need to replace it. This is why your old stove needed the neutral. The new stuff is more advanced and all its lights are probably LED and the power supply inside them takes the 240 V and adjusts it to the voltage (probably 24 or 12 V and likely DC) they require so no need for the neutral. If you look at your dryer, you likely have the same situation: 4 wires and the neutral is used to provide the proper voltage to the lights inside the dryer.

Just don't let Mrs. Chuck read this thread and you should be all right. :D