Amperage for 5HP table saw?

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See the disclaimer attached to my post. No, I'm not sure, because I didn't look it up myself; but I'm satisfied those guys knew what they were talking about. I'm comfortable with it. But then, I'm known for taking risks and living on the ragged edge. I used to hang off cliffs on ropes and ride motorcycles really fast. I don't have a guard on my tablesaw blade. And I used PVC pipe for airline. Don't do what I do. Do what makes YOU comfortable.
DonkeyHody If ignorance is bliss, why aren't more people happy?
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DonkeyHody writes:

Comfort is not the point. If you run an undersized wire, you're risking problems with the system that might become critical. If that system is part of your house wiring, failure could be fatal. I very much doubt the NEC allows a 40 amp breaker on 10 gauge wire, though many odd things are possible. I don't have even my old copies here to check, but your best source for a check will be your local building inspection office. After all, they have to pass your installation.
Another point: most electrical engineers of my acquaintance know very little about NEC and building codes in general. They have no need to know, unless their speciality is in some area of construction.
I've seen guys who can do a superb job of designing transport wiring systems for production lines that I would let wire the last motorcycle I had...and that was a bike without a headlight or taillight.
Charlie Self "There is nothing wrong with America that cannot be cured with what is right in America." William J. Clinton
http://hometown.aol.com/charliediy/myhomepage/business.html
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I'm anything but an electrician, but I learned early that the breaker is there to protect the wire, 'cause when wires fail houses burn.
djb
--
Is it time to change my sig line yet?

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30amp
John
On Tue, 02 Mar 2004 05:17:29 -0000, _firstname_@lr_dot_los-gatos_dot_ca.us wrote:

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I have a Left Tilt Unisaw with a 5 HP, single phase 230V, TEFC motor. It uses the full voltage motor starter (GPE). I have the saw connected to a 30 A breaker. The saw starts right up and has never tripped the breaker when starting or in use. While waiting for delivery of the saw, I talked to Delta technical support. They said I would need a 40 Ampere Slo-Blow Fuse. But as noted in earlier email, there is no such beast at Home Depot. Once I had the saw, I looked at rating of the motor starter. I was rated for 18-25 A devices. And I did verify that the motor was rate at 5 HP.
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I have a true 5 HP motor that is rated at 25 amps @ 230 volt. I did a quick check through a Grainger catalog and found only one 5 HP motor under 20 amps @ 230 volt. Most were 22-23 amps. Greg
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_firstname_@lr_dot_los-gatos_dot_ca.us wrote:

A web search shows that a typical 5 HP 230V motor draws about 24.5 amps. You could probably get away with a 30 amp breaker.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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Given that a breaker exists only to protect the wire connected to it and that is fact:
1) a 30A breaker connected to and protecting #10 wire will give (by your NEC code) 30 x 80% = 24 amps of continues current
2) You must get the FLA off the nameplate of the motor. Motors are ALL built with different efficiciencies and housing structures - therefore the only accurate current draw is that which was tested at the factory on their design model. Motors, at startup typically drew about 6 x FLA at startup, but today motors can easily hit 12 x FLA at startup because of lighter housing, thinner internal wiring etc - in otherwords the motors have been cheapened up.
3) If you motor nameplate, and it read 22 amps FLA - then you'd have 2 amps left over and you are good to go. If the motor nameplate on the other hand said 26 amps FLA you need to revisit the breaker/wire combination. It will still work but likely it will trip, maybe not for hours (only the breaker trip curve could answer that question) - the code can't stop you from attaching a 35 amp load to a 30 amp breaker combo - it just won't stay live very long.
The code derates by 20% to give you the easily calculated values that allow you to enjoy continuous power on a circuit. The derating comes from the fact that circuit breakers are thermal devices (BTW so are fuses) in that they have as part of their protection system, a bimetallic element that works on heat principles. Once you put a breaker in an enclosure, heat can build up and trip the breaker. Enclosure are build with minimum cubic inches of "cooling space" and in conjunction with the 20% derating rule offer you a product that can supply current on a continuous basis. Put that product in the boiler room of a ship, where the ambient temp is high and the breaker will trip sooner. Same applies to a "hot" woodworking shop - this is why the 20% derating. If you want to spend the money, you can buy 100% rated breakers which are certified as such and you can draw 100% of the current. These breakers start at 400Amp and go to 6000Amp.
Anyway, I digress - don't try to re-engineer some that has been designed for you and enforced by the NEC:
12A circuit = 15A breaker + #14 wire 16A circuit = 20A breaker + #12 wire 24A circuit = 30A breaker + #10 wire 32A circuit = 40A breaker + #8 wire
Once you pick the right size "service" - make sure you have the proper device to protect your motor - the upstream breaker has nothing to do with that - but that a lot more typing and I'm not good at that.
Regards John
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