In article ,
skeezics wrote:
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.
You're _legal_ with 20A breaker.
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?
If the device is 240V _only_, then 3-wire is code-compliant Hot1, Hot2,
and _ground_ (usually through the conduit itself; flex conduit or non-metallic
sheathed cable does require a ground *wire*). No neutral. If there's
any 120V 'stuff' in the device, (typically lights, timer, etc.) then a
neutral wire, in addition to the ground is required.
Recommendation: pull the neutral to the box, *even*if* you don't use it _now_.
Again, wire is cheap. and it gives the flexibility "down the road" to
run 120V equipment off that box. Or to slap up a double-gang box next to
the 240 outlet, with a pair of 120V duplex outlets -- one pair on each
side of the 240.