In article ,
Peter De Smidt wrote:
I'm trying to turn my 1-car, 70 year old garage into a workshop. At
the moment, it has two 15 amp lines run through 1/2 metal conduit.
The wire is 14 ga, and there are two hots, one neutral and a ground.
I'd like to increase this a bit. I was thinking of putting in a
sub-panel. I'd like to be able to run the new wires in the same
conduit, as it's a little too frozen here at the moment for me to dig
a new trench. My idea was to replace the 14 ga wires with 10 ga.
According to my sources, a 1/2 metal conduit will take 5 - 10 ga
wires, and so 4 should be no problem. My understanding was that if
the run was under 35 ft, that each of the 10 ga. hot wires would
support 30 amps, and hence that I should hook each hot wire to a 30
amp breaker in the main box. The salesman in the Menards electrical
section told me that this wasn't right. The four wire system would
only support 30 amps. Any comments?

-Peter De Smidt

Yes, 10 ga wire is good for 30A.

Depending on the number of bends in the conduit, it may be a difficult 'pull'.

For a sub-panel, you need 240V "to the panel". So, the 4 wires gives
you *one* 240V circuit, which will have 2 hot wires, each connected to
one pole of a 'double pole' breaker. This will be a 30A 240V breaker.