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Question DetailsAsked on 4/21/2015

need 220 volt -- have 120 at outlets - main shut off has double pole /single bar - each pole indicates 100-- Help

I read a double pole at main shut off breaker should indicate 220 Volt / my breaker box only has square D single pole breakers marked 120 / 240 -- my main shut off breaker is double pole single bar marked with 100 on each side of the cross bar--- I am confused--

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OK - 120/240 is the nominal voltage for houses in essentially all the US - commonly runs around 110V and 220V but varies by 5-10 volts during the day during low and high demand periods, so those numbers are interchangeable as far as incoming power. Your breakers would be labelled 120V and/or 240V.

The double-pole singlebar main breaker should be a double breaker (two individual breakers joined by a connecting bar so they flip together) or may be a double-wide breaker with one bar like this -

That is a 220/240V feed- each "live" wire passes through one side of the twinned breaker, so that one breaker is actually controlling two "sides" of the 220/240V feed, each ofwhich then feeds into the power bus or power bar on one side of the breaker panel.

In your breaker panel, you will have mostly single breakers something like this, and probably rated from 15-30A (amps) -

which have one "live" circuit wire leading into each one - those are your ordinary 110/120V circuits for lights and outlets and such. The return or white wiresand the green or baregroundwires do not go tothe breakers- they terminate all together at screw bus bars in the box where they are all tied to neutral or ground.

Your 220/240V appliances like electric furnace, electric water heater or whole-house tankless heater, electric dryer, electric range, central air conditioner, large power tools like compressors and large welders and saws, essentially all but very shallow wellpumps, and some dishwashers or clothes dryers with built-in steam generation all use double or paired breakers- like the first link I provided above, or in most other brands and somenewer Square D breakers twinned breakers like this -

with two much larger (and commonly aluminum) wire size leads to the two different screws, and it takes up two breaker slots worth of space in the breaker panel. That provides the 220/240V feed - 110/120V on each wire, whose sinusoidal power supply are out of "phase" with each other so the voltage difference between them is 220/240V, while each is 110/120V relative to the neutral and ground.

The 220/240V outlets for ranges and dryers and such have different prong arrangements than a normal outlet- usually in a Wye or triangle configuration, each different pattern designating a different amperage demand so you can't plug the wrong device into a circuit not suitable for it. Generally, houses are pre-wired for electric ranges and clothes dryers with the most common sized outlets for those devices, though an older house (especially pre-80's) might have undersized outlets for todays appliances.

If you have more questions, respond back with the Answer This Question link right under your question, or if considering electrical changes then Electrical is your Search the List category for contractors. You can also add photos, using the leftmost yellow icon right above the Your Answer box that comes up when you click the Answer This Question button.

Here is a link (a little ways down the referenced page) to a chart of the common plug/outlet configurations in the US for 120V and 240V. They are grouped by voltage and amperage - the -15 through -60 designations by each is the amperage for the outlet, assuming it is properly wired and has correct breaker back to the breaker panel.

Answered 4 years ago by LCD

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