"toller" wrote in message
...
It is not recommended. Anything confusing is dangerous, and this is
confusing.

Saw quite a bit of this debate on various NGs. Some felt it's dangerous
because someone will screw up the neutrals at a later time, or a future
homeowner might replace the double pole breaker with two, and put them both
on the same leg of the service.
Others thought, anyone qualified to work on the wiring or panel should not
be confused by this type of circuit.

However, if you lose the 30a breaker, it is possible. You cannot use a
30a breaker because the 120v circuit will not be rated for 30a. You must
get a 20a breaker and use #12 for all of it. (I am assuming #12 is
adequate, which might not be true if your run is too long and the current
is too high; you have to check that first)

This might be my downfall. It's not going to be practical to use 30A outlets
so the whole circuit can be considered 30A rated.

If 20a will cover the DC and whatever you want to also run on it, you can
do it. Otherwise you can't.

It's looking more like that's what I'll do... back to the original plan and
see how it goes. My thinking, though, was that now on a 15A circuit, I'll
have the breaker trip sometimes on starting a machine. Table saw - about 10%
of the time. Miter saw - maybe 15% of the starts. Planer - probably 1/3 of
the starts trip the breaker.
So I was thinking 20A circuit. But now add the dust collector, drawing 6A
continuous (12 on startup). Now I've got about 14A "headroom" for other
motors to start.

Overall it is a better idea to run two circuits. Did anyone mention that
you will need 12/3 wire for the combination circuit but only 12/2 for the
separate circuits? It is probably just as easy to run two 12/2 as one
12/3.

Yeah, I knew that. I'm running the wiring in EMT conduit though, so I don't
have to tear up finished walls. I thought I read somewhere that you can't
run more than one circuit in the same conduit run. If that's true, two
circuits means more cost.
I suppose another option is replace the 30A breaker with a 20A double-pole,
make it a 20A, 120/240V circuit. Could still use the 20A receptacles then.

Anyway, talked to my neighbor who referred me to another neighbor who's an
electrician. I may be able to get some inexpensive guidance from him.

That was funny about not being able to change DC to AC.