In article , Peter De Smidt wrote:
My plan was to install a subpanel, and then run the necessary 120 and
220 circuits off of this. At the moment, my only big piece of
equipment is a 2hp table saw. I'd like to rewire it for 220. At the
moment, I'm going to use my shop vac with a HEPA filter for dust
control, although down the road I'll probably want a 220 DC system.
For lights, I plan on using a 400 watt HMI light, and maybe a few
small task lights. Eventually, I hope to add a planer, jointer... but
these will only be run one at a time. For heat, I'm hoping to install
a used high efficiency furnace, but at the moment all I have is a 1450
watt space heater.


The circuit ampacity must be based on the heaviest loads that can be placed on
it *simultaneously*. In your case, that looks like table saw + dust collector
+ lights + heater.

A 2hp table saw doesn't draw the full 2hp most of the time. Likely continuous
load is in the neighborhood of 6A to 8A at 240V (1440 to 1920VA). A decent
240V dust collector is probably going to draw somewhere around 10A as well
(2400VA).

Figure about 2000W total for your heater and lights. (2000VA)

The dust collector, lights, and heater are "continuous loads" as defined in
the NEC and the ampacity of the circuit(s) supplying them is required to be
derated by 20%. Thus to supply the total of 4400VA for these loads, you need a
circuit rated at a minimum of 5500VA. Add 1440 to 1920VA for the table saw,
and you're at 6940 to 7420 VA -- which is 29 to 31A at 240V.

So a 30A 240V circuit is _just_barely_ adequate, and leaves you _no_ room at
all for adding additional loads.

And that's assuming that you're going to be able to pull three #8 wires
through a 1/2" conduit in the first place. :-)

--
Doug Miller (alphageek at milmac dot com)

How come we choose from just two people to run for president and 50 for Miss America?