120V vs 240V Discussion

A question often asked is: will my saw/jointer/planer run better on 240V (commonly and erroneously called 220V)?

Heh, heh. Reprising a well-worn topic. There are lots of folks who keep saying that because the power (P=IE) is the same that it doesn't matter. However, in the real world it usually does matter, and here's why:

If you had your voltage source real close to the tool, and it was capable of supplying all the amps you needed without any voltage drop, you would probably not see any difference, and there would be no power advantage.

In the real world, however, you likely have your tool at the end of a 20-30' run of either 14 or 12 ga wire. When you light the tool off at 120V (I'm not talking about the instantaneous starting current, just the normal current draw), you might draw something on the order of 8 amps (assuming a 1hp motor, for the sake of discussion). In this discussion, it's not important to know what the actual resistance of the wire is, there is some; let's call it R. Plugging in the values we see that E=8*R. E is the voltage drop at the motor from the current draw over the length of the supply line because of its resistance.

Now if you run the same tool on 240V, it only draws 4 amps (or thereabouts, but in any event, half of what it was on 120V). Plugging in the values you get E=4*R. This time E is only half of the drop that you had running on 120V (and we're assuming same wire size as at 120V).

Now just for grins, let's say the actual voltage drop was 10V at 120V, and therefore 5V at 240V. A 10V drop at 120V (roughly 10%) may be hugely significant in the performance of the motor. A 5V drop at 240V (< 2½%) is barely a bump on the road.

That's why tools run better on 240V than they do on 120V. Otherwise, watts is watts as the naysayers are fond of quoting.

There's one other thing worth throwing in the face of anyone claiming less heat, greater power, or better efficiency in the motor—most dual voltage motors have two sets of 120V windings. The jumpers you move on the motor merely changes how those windings are wired within the motor—in series for 240V operation, and in parallel for 120V operation. In other words, each coil always has 120V flowing through it, regardless of the source voltage. The motor can't tell the difference and doesn't care if it's jumpered for 120V or 240V.

The discussion preceding that, however, has to do with the actual voltage delivered to the motor.

Last updated: 27 January 2009