If I combine two 120v AC lines to get 240v, and each is on a separate 20a breaker, will I have 40a or 20a?



20 amps!

Pat F85

Typical U.S household current uses two (2) 120 volt lines, (leg 1 and leg 2) which are out of phase with each other, and one (1) neutral. If you tap two lines that are out of phase with each other, leg 1 + leg 2, each using their own 20 amp breaker, you will have 240 volts @ 20 amps . If you tap two lines that are both in phase with each other, leg 1 + leg 1 OR leg 2 + leg 2, each using their own 20 amp breaker, the voltage will remain the same @120, but the usable amps will effectively double to 40 amps. Your scenario suggests 240 volts @ 20 amps. Be careful, OK.


In effect, what you'll have is a "20amp" two-pole breaker ,,assuming that that both breakers are directly adjacent to each other to insure that your connecting those breakers to two separate poles in your 240v service panel, and they should be bridged together so they can both be turned on or off at the same time,,, But rather than use 2 separate breakers,, your best option is to just Buy a two pole Breaker at an electrical supplier or hardware retailer,,,& also check your circuit requirements to determine if your gonna need a grounding conductor in the way of a 'Neutral',,,


Combining L1 (120VAC@20A) and L2 (120VAC@20A) will result in 240VAC@20A. The supply voltage doubles but it is still a 20A load circuit, you still use 20 amp wires. The 2 pole 20A breaker will tap L1 and L2 when snapped in the load panel properly. When using separate breakers they must be on separate load poles or it's only 120V. As you look at the breaker panel, every other slot is L1 / L2 accordingly for this reason. This means that every 2 vertical adjacent breaker slots will alternate L1-L2-L1-L2 etc. It would behoove you to get a grip on how AC L1-L2 are each 180° of a full AC sine wave. When looking at the 240VAC line transformer link below you will see that 120V neutral is actually the 240VAC secondary output center tap on the power line supply transformer. https://electrical-engineering-portal.com/wp-content/uploads/2015/05/transformer-schematic-diagram.gif There are also what's called a 1:2 transformer that can double 120VAC@20A into 240VAC@8A. These buck back transformers are often used to run small 240VAC table saw type tool motors.

Dan B

20 amps. I won't go into the electrical engineering as to why only 20 amps - too complicated.


First DO NOT DO THIS. Never combine 2 single pole breakers to provide a 240 VAC feed. Remove two neighboring 120 V single pole breakers and eliminate the circuits they drove and insert a 2 pole breaker and run new lines to the desired 240 V point of use. Alternatively, if the breaker box has two neighboring open slots, install the 2 pole breaker there and run the new wires to the new circuit. If the 2 pole breaker is rated at 20 amps, you will have 240 v, 20 amp; if the 2 pole breaker is rated at 30 amps, you will have 240 v, 30 amps, and so forth. Be sure to use proper wire size for the load.


20 amps, but you can't just do that willy-nilly, you need both legs to get the 220/240.


Dude, you will be lucky I you only get electrified . That is a disaster waiting to happen. Hire an electrician if you need 220 for an appliance. 220 is not a general diy.

Spock (rhp)

technically, you'd get 20 amps at 240v -- IF and ONLY IF the two circuits reach adjacent breakers in the box. [or they are exactly an odd number of breaker positions apart, or ... it is best to test the potential across the outputs of the two breakers and make sure you're getting 220v before trying this] actually, this is exactly how a 220v circuit works in North America. You do have to make CERTAIN SURE that there is nothing else on either 110v circuit -- anything else on either will use part of the rated 20 amp output, potentially leaving insufficient for the 220v appliance. For this reason, the best policy is usually to run a new 220v circuit from the breaker box. Amperage does NOT add together the way you'd like to think -- amps measure volume of current flow, not the maximum potential [which is what volts measures]


NO. A double breaker at 20 amps is used.

The original Peter G

No, you'll probably get a big blue flash, then no power. Get a proper electrician to set you up.

Richard D

You will still have only 20. But in Watts you re double.


Depends how you combine and which wires you use to combine. If you connect two circuits so that you get 240v the you will only get 20A capacity. In US power systems a 240v circuit is two opposing 120v, each leg connected to opposite ends of the circuit. There are safety rules about using adjacent breakers with tied handles that apply. If you connected the wires from two breakers from the opposite leg together you would get a dead short that would at least trip a breaker, and if the breaker was unable to handle the short circuit capacity it could blow up at least one of the breakers. If you connect two of the same leg in a parallel configuration it would get 120v, it would take roughly 40 amp load to trip one of the breakers, the other would trip shortly after. If the internal resistance (due to age, abuse, design) varies between breakers it is possible it could trip below the combined amperage rating.