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for USA, Canada and countries running a 60 Hz power service.A service drop to a home is done with wire that is called triplex. This means that there are three wires twisted together that go from the service pole to the mast head on your home. This is called a three wire system. There are 2 hot legs and a neutral. The voltage between the hot leg (one) and the neutral is 120 Volts. The voltage between the hot leg (two) and the neutral is 120 Volts. The voltage between hot leg (one) and hot leg (two) is 240 volts. The single pole breaker is a safety device that connects to the (load, at 120 volts) and returns from the load back to the neutral. The load in most cases will be lights, plugs small appliances. The two pole breaker is a safety device that connects hot leg (one) to the (load, at 240 volts) and returns from the load back to the hot leg (two) at the two pole breaker. The loads in this case will be oven, range tops, hot water tank, clothes dryer, and in many homes baseboard heaters.


In USA 240V comes into your home even though most of your equipment is 120V. I say most because your clothes dryer for one, if you have an electrically-heated one, most likely runs on 240V. The answer to your question is that 2 legs (power lines) come into your house. One leg is colored Black, the other is Red.

Each leg is 120V to common (ground). The voltage is AC (Alternating Current) so it is always going from +120V to -120V on each leg. But at opposite times, so that at some point in the cycle one leg is +120V while the other leg is -120V. And if you measure the voltage difference between +120V and -120V you get 240V.

The US wiring system works like this: to turn on your lights you switch into one leg, the current goes through your wiring to your lights and back to common. But your dryer switches into one leg and returns the current to the other leg. If you look in your breaker box you see breakers on both sides. Looking straight across, these breakers are on the same leg (L1). The next set down the panel are on the opposite leg (L2). Adjacent breakers all the way down the panel are on opposite legs. A two pole breaker spans these adjacent legs and that is how you arrive at 240 volts. Your dryer is connected to a two pole breaker that taps into both Black and Red legs.


To accurately specify a voltage, you have to specify two points to measure, and the voltage is the difference between the two. If only one point is given it is usually implied that the second point is a grounded or 0 volt point. In the U.S., the three wires that enter most homes can be thought of as at +120V, -120V and 0V relative to ground. The 0V line is the "grounded" conductor, sometimes also called "neutral" and must be well connected to the earth where the wires enter the building (and no where else!) The +120 and -120 are actually different phases of an AC voltage wave. So by choosing which two points to connect to, a load can receive 120V or 240 V. Since there are two ways to get 120V, the breaker panel is usually set up to distribute the load between the two 120V phases.


As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.





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โˆ™ 2015-07-15 18:28:57
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Q: How can you run a 240V supply into your home when the circuit breaker is 120V?
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Related Questions

Can you run a 120V heater with a 240V supply?

Definitely not - it would burn out quickly and probably cause the circuit breaker to trip as well.

How much voltage should be in 2pole circuit breaker?

In America, a 2-pole breaker is controlling 240V. 120V per leg.

Can you convert a 240V circuit on your service panel to two 120V circuits?

A 240 volt breaker can be removed and replaced with 2 - 120 volt breakers. The existing 240 volt breaker should not be used to supply 2 separate circuits.

Can I use a 120v rated bulb in a 240v socket on a 120v circuit?


If your air conditioner is 120V but the outlet is 240V can you convert from 240V to 120V and how?

If the 220V circuit is dedicated, is to derate the circuit to a dedicated 110V outlet. Replace the 220V breaker with a 110V breaker and install a 110V outlet in place of the 220V outlet. If the original circuit was 20A or greater go with a 20A breaker and a 20A outlet as Airconditioners are fairly large loads. Do not exceed the current rating of the old circuit as that is all the current the existing wiring can handle.

Can you take single phase of 120V with a hot wire and a neutral step up to 480v and then step down to 2 phases of 120V or do you have to input 2 phases of 120v to get 240V out?

Theoretically that can be done with transformers, but the power available would still be limited by the circuit breaker on the original 120 v supply.

How do you upgrade from 120V 15A to 120V 20A or from 240V 20A to 240V 30A?

You have to replace the wire (as you are increasing the current capacity), the outlet, and the breaker. Essentially you have to remove the old circuit and put in a new one. You can't reuse parts of the old circuit as you are increasing the current capacity and they would be underrated.

How do you change a double pole 240v breaker to a single pole 120v breaker to allow a regular 120v receptacle to work?

See Discussion Page

Can you change a 120V to 240V without having to involve the circuit breaker?

In simple words, NO!!! On the first day of Electricity 101 they tell you if you do not know what you are doing, DON'T DO IT!!!

Can GFCI circuit breaker handle a 240V circuit with a 120V circuit sub-paneled off if it?

I don't know if you are trying to ask if you can run a 240V panel off a GFCI or run a 120 V sub panel off of a GFCI. Can you clarify please,,,Thanks

You are building a new house and trying to decide between 120v and 240v which is better More practical?

In the US, both 120v and 240v will be needed for your home, as different appliances need different voltages. Your TV needs 120V, while your electric dryer and stove will need a 120V/240V supply. If you have an electric water heater, or central AC unit, they will need a 240V supply.

Can you tap into a 240V circuit to get 120V?

On a pure 240V circuit, no. There is no neutral. On a 240/120V circuit, yes. You have the needed neutral. Tapping 120volts off an existing 240volt branch circuit with a neutral is possible but is not a proper method. It does not comply with most electrical codes.

How can you plug 2000 watts 240v into a 120v 20 amp breaker with out replacing your breaker and all the plugs on the line?

You can't.

How can you wire 120V to 240V?

A far as I know, you can't. If a wire is used in a 120v circuit, the wire itself is only rated up to 15 amps, therefore it can't carry a full load without tripping the breaker.

When going from 1-240v to 2-120v circuits do you need to replace the double pole breaker?

Yes, otherwise your double pole breaker will shut the other circuit off when one of them trips.

What happens when you supply only 120V to a 240V motor?

it won't work properly

Can you wire a 120V stove fan to the 240V supply?

No, you must break it down to a 120 volt supply.

What breaker do you use for 10-2 wire?

Assuming a 120V circuit then a 30A Single Pole. For a 240V circuit an 30A two pole. Of course anything smaller that a 30A is acceptable. 30A is the maximum allowed.

How do you wire a 15 amp breaker for 240v?

A single pole 15 amp breaker can only be setup for 120v. You need a double pole 15 amp breaker, which looks like two 15a breakers attached with a bar across the two actuators. Each leg provides 120v, or in the case of your breaker, 240v across the two legs.

Can you wire a 12 2 wire to a 20A 240V circuit breaker to get a 240V for an electric heater?


What gauge wire is needed for 240v?

The voltage has nothing to do with the gauge of wire needed to supply a given circuit. The size wire is determined by the amperage of the overcurrent protection device (circuit breaker, etc.) being used to supply power to the circuit.

Can a 240v 50amp circuit be changed to a 120v 30amp circuit?

Answer for USA, Canada and countries running a 60 Hertz supply service.Yes, a 240v 50amp circuit can be changed to a 120v 30amp circuit. The wire for the 50 amp circuit should be a #6. This is more than ample for a 30 amp circuit. Remove the two pole 60 amp breaker and replace it with a single pole 30 and a single pole 15 amp breaker. One of the two #6 wires will be terminated on the neutral bus (if there is a white use it) and the other #6 will be terminated on the new 30 amp breaker. This will give you the required 120 volt 30 amp circuit. The new 15 amp breaker that was installed just to fill the hole from the two pole 60 amp breaker will give you a spare 15 amp circuit. I have no idea what you are trying to do, but there is no way you can change 220v 50 amp to 120v 30 amp. You can take 220 volt input in the top of your circuit breaker box. Then half of one side will be 120v and half of the other side will be 120v. You can install a 30 amp fuse. You should hire an electrician.Before you do any work yourself,on electrical circuits, equipment or appliances,always use a test meter to ensure the circuit is, in fact, de-energizedIF YOU ARE NOT REALLY SURE YOU CAN DO THIS JOBSAFELY AND COMPETENTLYREFER THIS WORK TO QUALIFIED PROFESSIONALS.

What is 2 pole 20 a circuit breaker used for?

A two pole 20A circuit breaker can be used for any 240V load that requires 20A, with supply conductors no smaller than 12AWG. Since a clothes dryer typically requires 30A, and a range 40A to 50A, a 20A 240V circuit could probably be a window air conditioner, pool pump, or some other 20A 240V load.

What size amp circuit breaker should be used for 240V 7000KW?

For a 7000watts or 7kw a 240V then it is 30 Amp

How much can a 15W circuit breaker handle?

Answer for the US: Breakers are rated in amps, not watts. However, a 15A breaker can handle 15 amps, or about 1800 watts (using 120V), or 3600 watts (using 240V). However, this is only rated for noncontinuous loads (those not lasting for more than three hours). For continuous loads (loads lasting three hours or more), one must derate the circuit breaker by 80%. So for continuous loads, that same breaker should only have 1440 watts (using 120V), or 2880 watts (using 240V) on it.