Clarke,

I highly doubt that you will find an electrical inspector willing to pass a residential installation that protects a #10 conductor
that is protected by either a 40 or 50 A breaker. Even though the current carrying capacity of a #10 THHN is 40 A, the NEC limits
it to 30A. Can you get away with it? Probably. Will meet code and pass an inspection? I sincerely doubt it.

--
Al Reid

"It ain't what you don't know that gets you into trouble. It's what you know
for sure that just ain't so." --- Mark Twain

"Clarke Echols" wrote in message ...
First of all, be sure the person giving you advice is qualified to do so.
You're missing a lot of better input, so I'll give it a shot.

First of all, the NEC (National Electrical Code) specifies that circuit
breakers must be sized such that they do not exceed 80% of their trip
capacity under normal circumstances. If you are running motors that pull
high currents for a short time (saws, planers, jointers come to mind)
either at start-up or during operation, you work from maximum normal
operating current, not peak-load current. A #10 wire can carry 30 amps.
A 30 amp breaker is allowed to carry a steady-state load of 24 amps. Thus
you can use a 40-amp breaker on 30-ga. wire for motor loads (actually you
can use a 50-amp breaker if you're running an arc welder). Local codes
might vary, but I got this from a retired industrial electrician of
substantial experience. You have to go to the NEC and look in the area
that talks about motor and welding loads.

Since it's cold, I suggest pulling the 14-gauge wire and replacing it with
10-gauge with a 30-amp breaker. Run 4 wires, black, red, white, and green
into a subpanel in the garage. Put a 40-amp breaker in the main panel,
then connect the white to the neutral bus in the main panel and sub-panel,
connect green to the safety ground bus (where all the bare wires are)
in the main panel, and to the safety ground bus in the sub-panel. DO NOT
INSTALL THE BONDING SCREW IN THE SUB-PANEL! This is necessary in order
to keep neutral currents from flowing through the safety-ground wire
(required by code).

Connect the red and black wires to the L1 and L1 lugs on the sub-panel
and to the 40-amp 2-pole breaker in the main panel. Install a 20-amp
2-pole breaker for your table saw's 240-volt (not 220 -- that's a European
voltage) receptacle and wiring, then put in a pair of single-pole breakers
for two 120-volt, 20-amp circuits, using the normal wiring methods.

Then, when the frost is gone and spring/summer arrives, put in a bigger
conduit (1" would be nice, but it's a 70-year-old garage, so no sense
in overdoing things) and run #8 copper with a 50-amp breaker to the same
sub-panel. You can then put in a second 240-volt circuit, or just run
the TS and DC from a single 30-amp, 240-volt circuit with multiple
receptacles like I do in my 26 x 30-foot garage/shop.

I built my own home (7500 square feet plus garage) in the 1970s, and the
state electrical inspector took great pains to catch me on a code
violation. He came up with nothing. :-) I got my license as a
registered professional engineer in 1980, and have been wiring homes
from time to time since the 1950s. I also was responsible for
specifying wiring and grounding for industrial electricians in a
semiconductor manufacturing plant in the 1970s.

You really should get an electrical permit and have the work inspected
by local officials to protect yourself anytime you do this kind of work
if you are not absolutely dead-certain you know what you are doing. If
you don't, get someone who does to help you. Do-it-yourself books might
be useful, but they're no substitute for first-hand, first-rate knowledge
and experience, and wiring screw-ups can and have killed lots of people.

I saw a situation years ago of a homemaker who could have been killed.
She complained of sparks between washer and dryer. If she had touched
them both at the same time, she's have possibly been dead. Some idiot
"wired" 240V into the trailer for a dryer and got the wires on the wrong
terminals in the receptacle so there was 120 volts AC between the dryer
cabinet and the washer.

For more about overload protection for electrical motors as well as
grounding and other info, see

http://cnets.net/~eclectic/woodworki...arkeMotors.htm

Since you are considering dust collection, invest some time getting
educated on dust collection at

http://cnets.net/~eclectic/woodworki...lone/index.cfm

and when you're ready for a really exceptional cyclone dust collection
system in kit form so you can save some bucks and get the satisfaction
of building it yourself while getting first-class results, check out

http://cnets.net/~eclectic/woodworki...larkesKits.cfm

Clarke

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