Electrical Plugs and wiring and new to me equipment

[David Ashley]

So I have new "to me" saw with 2 motors 4.5HP at 18.2 Amps main and 1/2 HP 3.4 Amps score blade. 21.6 Total Amps, I know I could more then likely I would be fine on a 20 amp breaker but should I bone up to 30 Amps?

My plan is to use a 10 guage cord and 30 amp breaker... anyone think this is overkill?

I went to Lowes and started looking at plugs and wire, and started wondering which plug to use, they have the 3 and 4 prong Dryer looking plugs 14-30R, 6-30R funky looking version of a 110 outlet, L 6-30 and the twist locks. Assuming I use a 230V 30 amp plug does it really matter if I go with? Not to mention the twist lock ones are about 3X the cost...

Thanks everyone.

-David
New to me Laguna TSS

[Mark W Pugh]

So I have new "to me" saw with 2 motors 4.5HP at 18.2 Amps main and 1/2 HP 3.4 Amps score blade. 21.6 Total Amps, I know I could more then likely I would be fine on a 20 amp breaker but should I bone up to 30 Amps?

My plan is to use a 10 guage cord and 30 amp breaker... anyone think this is overkill?

I went to Lowes and started looking at plugs and wire, and started wondering which plug to use, they have the 3 and 4 prong Dryer looking plugs 14-30R, 6-30R funky looking version of a 110 outlet, L 6-30 and the twist locks. Assuming I use a 230V 30 amp plug does it really matter if I go with? Not to mention the twist lock ones are about 3X the cost...

Thanks everyone.

-David
New to me Laguna TSS

I'm not an electrician, but I would put the 30 amp breaker in. I would get a outlet and plug that matches other 220 outlets I have in the shop. I keep one style of outlet in shop. I'm sure someone with more experience will chime in.

[Ole Anderson]

Both motors appear to be 220 volt by their amp draw so you need a three prong outlet/cord, one ground and two hots. And yes you need a 30 amp circuit. No need for a twist lock unless you are hanging cords from the ceiling. Feed the outlet with 10-2 (wg) wire, but you could probably go with 12-3 for the cord from the saw to the outlet if you choose the proper wire, some are rated from 25-30 amps, others only 20 amps.

[Rod Sheridan]

Hi David, I run my 4HP slider on a 15A branch circuit.

That said, put in a 30 A circuit and use straight blade devices, not twist locks.

Regards, Rod.

[Wade Lippman]

I would ask the manufacturer what they recommend. If it is really 21.3a then you must have at least a 30a circuit; possibly a 40a circuit. The same plug as on 20a circuits would be quite improper.
Likewise, I can't imagine why 12/3 for a cord would be recommended over 10/2. I suppose the additional voltage drop in an 8' cord would be small, but why do it? And why /3?

[Mike Wilkins]

I utilized the twist-lock plugs for my 240 volt 20 and 30 amp machines. Call it overkill/anal/over-cautious/whatever, but you can use the straight lug plugs and life will go on. I sometimes over-think these things. I am not a production shop, just a single shop, serious amateur wood butcher.

[Sam Layton]

Hi David,

A 30 amp circuit is most appropriate. You must use a 10 gauge wire for the 30 amp circuit. Like Ole said, you need a ground and two hot wires. When you select a plug, you should use a three prong plug. If you have other 220, 30 amp tools in your shop, use the same plug type. What ever plug you use, just make sure it is rated for 220, 30 amps.

I use twist lock plugs for all of my 220 tools. The twist lock plugs are heavy duty, and stay connected. However, they are not necessary, just what I like. I would also use 10 gauge wire from the plug to the machine.

Good luck and enjoy your new saw, Sam

[Ken Combs]

Not all 3 pin 240v plugs are equal. Some (old dryer type) have two hots and a neutral, not a ground. Here is a good reference chart. When reading it, remember that if there is no 'g' pin, it is a 120/240V ungrounded, like the Nema 10 series.
I would select a NEMA 6-30 series plug and recept, with 10ga wire all the way.

Design load for a circuit should not exceed 80% of it's capacity per the NEC. So a 10ga/30 amp circuit can safely support 24 amps continuously. a 12ga cord is only rated for a 15 amp continuous load., 80% of the 20 amp rating.

[John Lanciani]

... So a 10ga/30 amp circuit can safely support 24 amps continuously. a 12ga cord is only rated for a 15 amp continuous load., 80% of the 20 amp rating.

That is just completely incorrect. Per the manufacturer; http://cmewire.com/catalog/sec19-FCX/FCX-Cu-01-AMP.pdf 12-3 S cord is rated for 25 amps continuous in this application (two current carrying conductors). NEC ampacity rules and derating requirements for permenantly installed building wiring do not apply to cord and plug connected equipment.

[Erik Loza]

I am a big fan of twist-locs, myself.

Erik

[Rick Moyer]

Just my take, but I always felt that if I ever did something stupid, I think I'd prefer that the plug came out of the outlet as opposed to the cord tearing and having bare live wire laying there. (sorry, slightly off topic).

I am a big fan of twist-locs, myself.

Erik

[Erik Christensen]

if it was me - I would wire for 30 amps including plug but start out with a 20 amp breaker. as long as you don't start both motors at the same time you are unlikely to trip the 20 amp breaker. the breaker is to not only protect the cord & plug but also your motors - bigger is not better as it takes a larger current surge (and therefore damage) to trip the breaker - the 30 amp cord may be OK but your motor might not

you trip the 20 amp more than rarely then you can go to 30amp with a new breaker

[Art Mann]

I have to disagree, Erik. There is almost no chance that a 20A breaker will protect a device where as 30A breaker will not. I can explain why if you like but it is a long discussion and requires some knowledge of electrical engineering.

[Ken Combs]

That is just completely incorrect. Per the manufacturer; http://cmewire.com/catalog/sec19-FCX/FCX-Cu-01-AMP.pdf 12-3 S cord is rated for 25 amps continuous in this application (two current carrying conductors). NEC ampacity rules and derating requirements for permenantly installed building wiring do not apply to cord and plug connected equipment.

I guess it's in the intended use and interpretation of the loads, a 10ga ciricuit has an ampacity of 30. The 12 ga cord set has an ampacity of 25. But, in my interpretation, neither should be loaded above 80% of their respective ampacity in continuous use. For a portable tool that likely will only be used for short periods that may be fine.

But, a table saw, planer, stationary sander or other similar tools may well be used for several minutes (hours?) without rest.

[John Lanciani]

I guess it's in the intended use and interpretation of the loads, a 10ga ciricuit has an ampacity of 30. The 12 ga cord set has an ampacity of 25. But, in my interpretation, neither should be loaded above 80% of their respective ampacity in continuous use. For a portable tool that likely will only be used for short periods that may be fine.

But, a table saw, planer, stationary sander or other similar tools may well be used for several minutes (hours?) without rest.

Continuous load is actually explicity defined by the NEC - NFPA 70-2014 Article 100-1 "Continuous load. A load where the maximum current is expected to continue for three hours or more." There isn't a home shop in the world pushing a machine at "maximum current" for 3 hours straight.

Further, continuous duty is defined as "Operation at a substantially constant load for an indefinitely long time." This doesnt sound like normal home shop use to me, either.

Additionally, #10 copper is derated to 30 amps for NM cable, in a wire in pipe installation where all of the components are rated for 90 deg. C, the ampacity of #10 copper with THHN insulation is 40 amps.

Also, NFPA70-2014 table 400.5 covers ampacities of flexible cords and it mirrors the link I posted above. #12 S cord with two current carrying conductors is rated for continuous use at 25 amps at 30 deg.C ambient temp. No need for interpretation, its all very clear.