I was talking to my brother and he's saying that 220v is the same total amps as 120v. Just that each leg is half the amps but since their are 2 hots is the same amps. Example I have a saw that is 15 amps at 120v but at 220v the name plate states 7.5 amps. So is he correct? I want to know if it is really half at 220v.
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220v half total amps or same?
- Thread starter Bigfork G
- Start date
theoldwizard1
Well-known member
For an electric motor, switching from 120V to 240V it will draw 1/2 the current (amps).
Few other types of loads can easily switch from 120V to 240V.
Few other types of loads can easily switch from 120V to 240V.
Speedy Petey
Well-known member
IF something, like your saw, is capable of being run on 120v or 240v then yes, the amps are halved.
At the same time, a 15A load @ 120V, and a 15A load @ 240V, are both 15A loads. What has to be considered is the watts.
15A @ 120V = 1800 watts
15A @ 240V = 3600 watts
For an example like your hypothetical saw:
15A @ 120V is 1800 watts
7.5A @ 240V is 1800 watts.
At the same time, a 15A load @ 120V, and a 15A load @ 240V, are both 15A loads. What has to be considered is the watts.
15A @ 120V = 1800 watts
15A @ 240V = 3600 watts
For an example like your hypothetical saw:
15A @ 120V is 1800 watts
7.5A @ 240V is 1800 watts.
Mr. T
Well-known member
Ohm's law is a law... The only practical reason to use higher voltage is to save copper. Everything else is a wash. It's the same power doing the same work, just split up differently.
the total draw is still the same, just 1/2 on each leg instead of total draw on 1 leg. there is no power savings running on 220.220 just basically means you can use a smaller gauge cable than you would need for a 110 volt draw.
My intent is to reduce my total amps on my panel while using a few more things. I'm not trying to save money on electricity. I have 50 amp at the garage but I can use them all if I'm running at 120v, so my thinking is run what I can on 220v and and half what I can then I'm OK.
you wont save total amps on 220. the total load is still the same
popbigguy
Well-known member
I know by Ohm's law, everything should be the same. But I switched my table saw over to 220 from 110 volts and WOW!!! What a difference it make in how it runs! I'll never go back to 110 again on a saw!
justsam
Well-known member
I know by Ohm's law, everything should be the same. But I switched my table saw over to 220 from 110 volts and WOW!!! What a difference it make in how it runs! I'll never go back to 110 again on a saw!
Actually by Ohm's law it is not the same.
Running at 120VAC you are drawing twice the current that you are at 240VAC, there fore you have twice the voltage drop in the circuit feeding the motor. This would include the line cord, and the wiring feeding the socket that the cord is plugged into. When saws are working hard, current goes up, and so does voltage drop which manifests itself as the saw "bogging" down.
Communication breakdown on all fronts. You are both right depending on the POV. Your brother is correct in that, for a given breaker size and wiring, each leg of 240v will safely SUPPLY the same amount of amps as 120v circuit. They won't draw as much due the current draw which is of course half for a 240v motor vs 120v motor if the watt output is the same. The advantage of 240v is you may operate a more powerful motor for a given wire sizing than 120v.