Yes. Doesn't the saw's manual tell you what size breaker to use?
You can't use a bigger breaker without ensuring that everything after
it is also rated for 30 amps, at least the hard-wired stuff (wire and
outlet). The purpose of a breaker is to protect the house from wire
insulation failing from heat, and starting a fire. The breaker is NOT
intended to protect your tools, although it can.
You can use bigger wire with a smaller breaker, to get the protection
you need yet reduce the resistance of the wire. You can't use a
larger breaker with a smaller wire, though.
Unless you're really far from the breaker, a larger wire won't make
that much difference. Larger wire reduces the resistive losses
somewhat, but the shorter the wire, the less an impact this will have.
A larger breaker won't do squat for you.
Larger wire is, however, more expensive and harder to work with.
10-2 with ground, a 30A plug and receptacle will make your life easy.
It is legal to use a tie handle most places, but DON'T do it.
A 2P-30A c'bkr with internal tie is not that expensive and offers added
You're on the right track standardizing on 30A circuits.
Basic rule of thumb for c'bkrs used on motor circuits:
A c'bkr needs to be sized about 2.5-3.0 as large as the FLA of the motor,
rounded up to the next std size c'bkr, in order to handle the inrush current
of the motor.
Thus, FLA.5 x 2.5 = 31.25A
And, FLA.5 x 3.0 = 37.25A
I'd try a 2P-30A; however, would not be surprised with an ocasional trip.
You could very easily use a 2P-40A for this application and be legal.
What does the saw mfg spec?
Puhlease. A 3HP saw occasionally tripping a 30A breaker? In what
universe do you think that can happen? You'd be unlikely to ever get a
trip on a 20A circuit with a 3HP saw. Maybe if he had 200' of feed,
but not in a normal run. 40A is more than twice as ridiculous as 30A
is in this application.
Not just the Uni--I have that same plug on my DJ20 and on my
DC380--all 3HP motors.
Unless Doug corrects me, I believe the use of a 6-15 receptacle on a
20A 240V circuit is permitted by the same exception as the 2-15 on a
20A 120V circuit is. Those -15 receptacles aren't "rated" for 15A,
they're "keyed" for 15A. In any event, I think all of that goes out
the window if it's a single receptacle and the only one on the circuit
(note a duplex receptacle is not a single receptacle).
It doesn't "need" to be sized that big.
For dedicated motor loads it's *permitted* to use an oversized breaker
should it be required. I have a 3HP motor on a 20A circuit, and I've
yet to trip the breaker.
3HP motor (Jet JTAS10) on a 240V/20A circuit now for more than 5 years
without a single trip, nuisance or otherwise.. I don't know where all
this "gotta have a huge breaker to avoid nuisance trips" BS is coming
from unless they're thinking about a 110V circuit.
There could be some justification in that case, 'cause a 110V/20A
circuit might be a little undersized for the FLA of a 3HP motor.
3HP = 2238 Watts = 20.35 Amps at 110 Volts (ignoring Power Factor,
A 20A circuit in the case of the OP certainly isn't "cutting corners."
In fact, it's more than adequate. 30A is decidedly overkill for 3HP @
240V (and will get Rick Christopherson positively apopleptic--and
rightly so). YOU recommended 40A. CYA? Please. That was just plain
Yes, if the circuit is wired with 12ga or larger wire
If you use a 30amp breaker, you need 10ga or larger wire. 30 amps is
more than you need for this application, and 10ga wire is larger than
needed unless you have an excessively long wire run from the breaker
to the outlet.
Yes, NEMA 6-20 configuration, if you use a 20 amp breaker
You'll spend more on wire (you may use 12ga wire with a 20A breaker, but you
must use 10ga wire with 30A), and you will be required to use 30A receptacles.
Using 10-3 (or 12-3) is pointless -- a 240V motor doesn't have, or use, a
neutral. All you need is two hots and a ground. 10-2 (or 12-2) is sufficient.
Again: you'll spend more on wire, and you'll be required to use 30A
receptacles. Code does not permit the use of anything but 30A receptacles on a
No. That will function as a double-pole 15A breaker.
Use a double-pole 20A breaker. Whether you use 12ga or 10ga wire is up to you,
but unless the saw is a long way from the breaker box, you're not likely to
see any benefit from the 10ga. Either way, though, use a 20A breaker, not a
Doug Miller (alphageek at milmac dot com)
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