Wiring and plug for a 3 hp cabinet saw

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Right, I gotcha -- but the OP had already stated his intent to use a 20A receptacle, and I wanted to emphasize that that was a no-go with a 30A circuit. Sorry for any confusion.
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Doug Miller (alphageek at milmac dot com)
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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.
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Even if that were legal and wise, it would still only give you a double pole 15 amp breaker, not 30 amp.
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"David Todtman" wrote:

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 protection.
You're on the right track standardizing on 30A circuits.
Have fun.
Lew
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"David Todtman" wrote:

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.
Lew
What does the saw mfg spec?
Lew
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On Mon, 15 Oct 2007 00:26:18 -0700, "Lew Hodgett"

Cite, please.

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.
--
LRod

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"LRod" wrote in message

... and, in the past the plug that comes standard on the 3HP Delta Unisaws is a NEMA 6-15P. It will work with a 6-15R, 15A receptacle, as well as a 20 amp, 6-20R receptacle.
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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).
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LRod

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wrote:

Exactly right, LRod.
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Doug Miller (alphageek at milmac dot com)
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So according to you, my 14.5A table saw should be on a 40A breaker.

Oddly enough, I've had that saw on a double-pole 30A breaker for five years now, with no trips -- even when ripping 12/4 hard maple. I'd be *very* surprised if the OP ever trips a 30A breaker.

As long as he uses a 40A receptacle, yes.
He could also use a double-pole 30A or 20A and be legal, and still not have to worry about nuisance trips.
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Doug Miller (alphageek at milmac dot com)
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Lew Hodgett wrote:

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.
Chris
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On Mon, 15 Oct 2007 09:29:19 -0600, Chris Friesen

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, Efficiency, etc.)
Tom Veatch Wichita, KS USA
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"Chris Friesen" wrote:

INRUSH!
Totally dependant on application.
Most wood working applications do not start under load, so the application is not that severe.
Lew

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On Mon, 15 Oct 2007 13:30:45 -0700, "Lew Hodgett"

Then the relevance of factoring it into your "recommendation" in this discussion is...?
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"LRod" wrote:

CYA.
For the amount of effort required to do the wiring, makes no sense trying to cut corners with tinkertoy components to save a couple of $.(Wire & wiring devices only)
Lew
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On Mon, 15 Oct 2007 14:47:14 -0700, "Lew Hodgett"

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 nuts.
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On Mon, 15 Oct 2007 02:45:37 GMT, "David Todtman"

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 need a 30amp receptacle, NEMA 6-30

NO, it would function as a 15amp breaker.

Tom Veatch Wichita, KS USA
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David Todtman wrote:

Same as my saw which is on a 20 amp circuit. Starting the saw will occasionally trip the circuit breaker.
--

dadiOH
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Curious: what's the nameplate amperage rating on the saw? How far is the receptacle from the breaker box? And is the circuit wired with 12ga wire as it should be?
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Doug Miller (alphageek at milmac dot com)
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Yes.
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 30A circuit.

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 30A.
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Doug Miller (alphageek at milmac dot com)
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