skeezics wrote in
:

On Wed, 28 Jul 2004 15:29:29 +0000,
(Robert Bonomi) wrote:

In article ,
skeezics wrote:
im wiring my shop and have 2 pieces of equipment i am not sure of. a
true 3 hp compressor and a 3 hp unisaw. is a 20 amp circuit enough
for each or these or do i need to go to 25 or 30 amp? the compressor
says it needs 15.4 amps and the tablesaw says 15.5 amps. thanks all
...

NEC limit for permanently attached devices is 80% of breaker rating.
Which is 16A for a 20A breaker. So, you're OK on _that_ basis.

Then, there is the issue of 'start up' load, vs 'running' load.
Virtually any motor draws more power spinning up, than it does
running 'at speed'. However, with the table-saw, the start-up
current draw is _probably_ not going to approach the draw of a
maximum-load cut. The compressor probably has 'smarts' so that
the motor starts up 'unloaded', and then picks up the load.

Me, I'd 'over-engineer' the solution, and see what happens. After
all, wire is _cheap_. Pull 10 ga. wire, and use a 20A breaker,
initially. Preferably a 'motor rated' (or slo-blow) one, if I can
lay hands on it. In the context of _that_ wiring approach, If the 20A
breaker trips too frequently, it _is_ safe to replace the 20A breaker
with a 25A or 30A one.




i didnt think about the startup draw. thanks. this is going to be
permited and inspected also. im thinking 30 amp is the best way to go
but i am not sure if i can use a three wire plug or if i have to use a
4 wire plug and change all my equipment over to 4 wire. i know i need
4 wire for such things as dryers and stoves but that seems to be
overkill for ww equipment. any ideas?

skeez

I asked my electrician, who is also a woodworker. We put in a 30 amp
circuit for my new Unisaw a couple of years ago. With a twist lock
receptacle.

We also put in a master cutoff switch, with a place for a padlock, to lock
out everything on the new subpanel. The lights are on the old subpanel, as
are the plugs for the freezer, and non-shop tools. I don't want
unsupervised use of the shop by my grown sons, until I'm certain they have
a little more experience and safety training. They didn't take shop in
school...

A master electrician did it right, and I don't worry about it. I have
enough to be concerned about.

Patriarch