Originally Posted by
Dan Friedrichs
Sure, but I think what usually happens is:
1) Someone decides their equipment isn't working to his satisfaction on a shared, undersized, long-run, 120V circuit
2) He decides to correct this by installing a dedicated, short-run, heavy-gauge circuit and use 240.
3) Tool works "way better". Must be because of the 240.
If that same new dedicated, short-run, heavy-gauge circuit were run on 120, you'd likely get just as good of performance, it's just that few people do that, because they've been convinced that "240 is better!"
In retrospect, I wish I hadn't bothered with 240V circuits in my garage - they limit where I can move equipment. There is a certain convenience factor of having 120V standard outlets everywhere, versus a mix of 120 and 240.
There are really only a few reasons to run 240:
1) You have a motor large enough (7.5HP+) that can't be run on 120
2) You are running new circuits, and the incremental cost of heavier-gauge wire (for 120 circuits) is significant enough that you're willing to forgo convenience for that cost savings
3) You have an existing circuit that would be undersized at 120, and you don't want to replace it, so you'll switch the motor to 240
I don't disagree with your primary thesis but I would say that most of us wire our shops with 12 gauge wire, which is too small for a 7.5HP motor at 120V. I don't even know if they make 7HP motors that will run on 120V.
My recommendation - for a normally wired shop, say with 12 gauge wire - is to go 240V for anything over 1.5HP.
The big advantage of staying 120V is flexibility - it's much easier to move tools around. Once you go 240V you'll probably have to run new wire if you rearrange your shop.
Mike
[But I do agree that with a proper circuit, motor performance will be the same at 120V as at 240V. Most people who have problems running a motor on 120V have a circuit problem.]
[And to address the comments about "balanced current" on the feeder wires: It doesn't matter if there's current flow in the neutral between the grid and your main box. The neutral wire in that circuit is sized to take the full current flow - it's the same size as the two "hot" wires. I can't think of a single problem with having current flow in that wire.] [And, of course, the current flow in the neutral will be the difference between the current flow in the two hot wires. So if one hot is carrying 20 amps, and the other hot is carrying 10 amps, there will be 10 amps flowing in the neutral.]
Last edited by Mike Henderson; 08-24-2015 at 11:16 AM.
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