Can we use each hot wire from 220v line separately

13 years ago

We live in California. Years ago, we replaced an electric cook top with a gas cook top. The installer used one of the hot wires from the cook top 220 line to put in a 110v receptacle box in our lower cabinet, and we plug the gas cook top into one of the two outlets. The other hot wire from the 220v line is capped inside the receptacle box. We are now replacing our old and anemic vent hood with a more powerful hood that is rated at 10 amps. We decided to also replace the very old hood wire and discovered that it is tied into the circuit that includes several kitchen plugs. I read that the hood should be on a dedicated line, or, if need be, on the kitchen overhead light circuit. To use either of those approaches would require a great deal of extra work and cost. The hood wire is only about 5 feet above the 110v receptacle that we use for the gas cook top. We can easily get the new hood wire down to the receptacle. Can we safely connect the new vent hood hot wire to the now capped hot wire in the 110v receptacle, and then connect the neutral wire from the hood to the 220v line's neutral wire that is in the receptacle and that is currently connected to the receptacle? If not, can we bring the hood wire down to the receptacle area, have it exit the wall, attach a plug and then stick the plug into the unoccupied outlet? If not, are there any other simple solutions. Thanks.

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Comments (7)

fa_f3_20
13 years ago
What you want to do is called a multiwire branch circuit. It's permitted if you do two things: (1) you must breaker the two hots using a double-pole breaker, and (2) the two hots must be on opposite phases of the service (which, with modern breaker boxes, will happen automatically when you use a double-pole breaker).
DavidR
13 years ago
One thing could throw a wrench into your plan - if the range circuit has only 3 wires (2 hots and a neutral), with no separate ground. It was once permitted to wire ranges that way, but no more.

If you don't have a proper, separate ground in the box, you'll have to pull a new homerun back to the panel. This can be a multiwire circuit as Fa describes above, and that way the old gas range receptacle will also be properly grounded (if it wasn't before).

If the old box IS properly grounded with a 3-wires-plus-ground feeder, then hurrah! But don't forget that you'll still need to install a 20 amp double pole breaker in the panel to replace the old 40 or 50 amp range breaker, if that hasn't already been done.

When you do this, you may find that the large wire to the range won't fit into the lugs on the 20a breaker. In that case, you'll have to use smaller pigtails from the breaker, and splice them to the range circuit wires.
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Ron, I can't see the need to get hostile toward anybody on this topic. You and I and many others have lots of experience with cabling. I agree with your statements as my comment stated. In our power plants we brought the Belden twisted pairs into the cabinets with the jacket stopped at times a foot and a half or more from the device, (RTD monitors, recorder or PLC, or what ever), and untwisted the pairs because they went to different locations. This never caused a problem. As you know what does cause a problem or can cause one is grounding the shield at both ends of the cable. We usually had a 5 or 6 ft long copper ground buss that we made up( drilled and tapped) and mounted it in the cabinet. There we terminated the bare shielding wires from the many cables. Soldered Burndy lugs on all ground and signal carrying conductors. Clamp or pressure terminated wires were used on some equipment that had those kinds of terminations, however they were avoided as much as possible. One problem with them was it made it harder to lift and lay back down the wires during troubleshooting or testing as the wires fray and are difficult to get back under the screw, especially when energized. And we had one guy that always made the strands of wire look like a worn out paint brush when he laid down those wires. At least 1/4 of the strands were sticking out. Terrible! One time we got a new pre-wired cabinet in from a manufacture and when we were putting the equipment into service it was not working. So naturally we looked at our own wiring and found no wires laid down wrong. After much troubleshooting we found where the manufacture had stripped the wire correctly but got the insulation under the screw where the conductor did not make contact. Boy that drove us crazy! Anyway, from one old sparky to another, good luck.
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From the sound of it, the $215 might be well spent. Besides, $215 sound WAY cheap to do a job like this. You are under the typical misconception that "110" and "220" are all that matters. An electric range is normally a 120/240v load, requiring a 4-wire 120/240v circuit and receptacle. This circuit has two hots, neutral and ground. Next is the amperage. How big does the circuit need to be??? "220" or 240v has NOTHING to do with capacity. Again, a typical free standing household range would be on a 40A or 50A circuit. The easiest way in a finished setting would be to use a surface mount range receptacle. Does the $215 man have insurance? License (if required)? A real truck and tools? If so then I suggest have him do it. If you are very confident that this is something you want to attempt then post back any other questions you might have.
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brickeyee
13 years ago
"the two hots must be on opposite phases of the service"

How do you get another phase from a one phase service?
kurto
13 years ago
Brickeyee,

Even though the phase nomenclature is incorrect, and typical US residential service is referred to as "single phase", the advice was sound. From an EE perspective, the two 120V legs (RMS measured with respect to ground) are 180 degrees out of phase with each other. (But you already knew that, probably better than anyone else on this board).

Kurt
ramrem
Original Author
13 years ago
Thanks for helping us out. Our line does have the ground, and I am looking for a double pole breaker.
brickeyee
13 years ago
"Even though the phase nomenclature is incorrect, and typical US residential service is referred to as "single phase", the advice was sound. From an EE perspective, the two 120V legs (RMS measured with respect to ground) are 180 degrees out of phase with each other. (But you already knew that, probably better than anyone else on this board). "

The 120/240 V system used for residential power in the US is an Edison circuit, just like a multi-wire branch circuit.

It is NOT 2-phase.

2-phase was experimented with long ago to allow for starting torque in induction motors (wit single phase power an induction motor has zero starting torque).

2-phase was discarded when 3-phase power proved easier to distribute.
2-phase uses a 90 degree phase shift and minimum of four conductors.
3-phase power requires only three conductors for a delta configuration.

The more common (and far more correct) description of a 120/240 V service is as legs, to make sure they are clearly differentiated from a 3-phase system that uses 120 degrees of shift.
DavidR
13 years ago
The 240/120v home mains is nothing more than a center tapped transformer. The tap is the neutral.

Those of us who spent our early years keeping company with tube amplifiers might be more accustomed to the idea of center-tapped transformers, as used in push-pull output circuits and full-wave 2-rectifier power supplies. (Old timers: remember 5Y3s and 5U4s? Selenium rectifiers were supposed to be an improvement! :)

Another model could be made with flashlight cells. Take your basic 2-cell battery holder and stick a paperclip or something between the cells. Now you have a center tap, and can derive two 1.5v circuits or one 3v circuit. This is great for experimenting to help understand how the mains work. For example, with an ammeter, you can convince youself that when the 1.5v loads are perfectly balanced, the center tap (the "neutral") carries no current, and that in all other cases it carries only the difference current.

Can we use each hot wire from 220v line separately

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Can we use each hot wire from 220v line separately

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