In article nDKyd.6899$k25.6498@attbi_s53, "Keith Carlson" wrote:

I was just thinking about this on the way to pick up pizza. With 10AWG wire,
I'd have a circuit capable of 30A, but the cords from all the tools are
110V/15A. (leaving out the Dust Collector for a moment). Those will plug
into 20A receptacles, so say I wire 20A receptacles on the 120V outlets. Now
suppose the planer or whatever manages to load down and wants to pull
something like 28 amps. The circuit breaker says "no problem". Could run
that way all day and it wouldn't trip. But what about that receptacle that's
rated for 20A??

Yep, that's a problem. Hence toller's statement that your 120V circuit isn't
rated for 30A. Technically, that's not exactly correct: there's no reason that
you can't have a 120V 30A circuit, as long as the wire is 10ga copper or
larger. But you're probably not going to find any receptacles that you can
plug a 15A or 20A tool into, that are rated for 30A.

Are the connections or conductors inside it going to
overheat?

Not if you don't feed current through it to some downstream load, *and* the
load you have plugged into that outlet never overloads. But if either of those
conditions occurs, yes, there is indeed a risk of overheating and fire.

Might be some risk there, not to mention the tool itself like you
say. I should go look at my reference book; NEC probably doesn't allow a 20A
rated receptacle on a circuit protected to 30A.

Right, it doesn't.

Then there's 120V/30A receptacles. Haven't looked, but probably cost more
than the 20's. The 110V/15A plugs won't fit in them, so I'd have to change
plugs on the tools.

Right on both counts.

Even then I have to consider how likely it is that I'll
have situations where the tool wants to pull more than its rated current.

Not relevant -- you have the same issue with a 20A rated receptacle on a 20A
circuit.

The 3-wire circuit starts to look like more trouble than it's worth. It
sounded like a slick idea at first, because I have the breaker, and I'd be
able to run 3 wires + ground in my conduit. (Finished walls, and I'm not
going to tear them up, so I'll be running EMT and individual wires inside).

Have you considered that when you rewire the dust collector for 240V, it will
pull only half as many amps? This may enable you to run the DC on a 20A
circuit, which you could wire with 12/3 and then add standard 15A or 20A 120V
receptacles. (Code *does* permit 15A-rated receptacles on 20A circuits.)

--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

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