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what gauge for 3hp Unisaw leed in wire?

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Forum topic by KipD posted 03-03-2018 03:29 AM 464 views 0 times favorited 7 replies Add to Favorites Watch
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KipD

17 posts in 294 days


03-03-2018 03:29 AM

1989 34-806 type 2 Unisaw has new Leeson 3hp single phase 230V motor 120728.00, with full load 13 amps. I would like to put a longer lead in wire- like 15 to 20’. I am using 6-20 NEMA type plug/receptacles. I have some nice Carol SJO 12-3 12 gauge wire. I want to know if this meets requirements. I contacted Leeson- and they referred me to some distributors. But people couldn’t tell me- or possibly didn’t understand what I was asking. I’m not asking about the wire being run in the walls- I’m talking about the wire that’s connected to the table saw that’s got the male plug that goes in the wall. I’m pretty sure 12 gauge is fine for a standard 8 or 10 foot power cord (and I think stock may be 14ga?)- but I don’t know what length before you have to switch to 10 gauge. I know….. 10 gauge “would be nice”- or “adequate”. But I would like to know how to calculate minimum wire gauge needed at longer lengths.

Thanks, Kip…...


7 replies so far

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MrUnix

7046 posts in 2400 days


#1 posted 03-03-2018 03:50 AM

12ga is fine. (here is a handy chart)

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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ArtMann

1142 posts in 1017 days


#2 posted 03-03-2018 04:05 AM

Let’s just do a little math here as an example. Suppose you have a 25 foot extension cord and the saw is drawing 13 amps. The current actually has to travel through 50 feet of wire.

10 AWG is about 0.00125 ohms per foot. The voltage drop would then be 50 X .00125 X 13 = 0.81 volts drop

12 AWG is about 0.0016 ohms per foot. In this case 50 X .0016 X 13 = 1.04 volts drop

14 AWG voltage drop would be 50 X .0025 X 13 = 1.63 volts drop

AS you can see, 12 AWG is more than adequate and 14 AWG isn’t all that bad, assuming the voltage starts off at the right level. You are right in assuming that the length of wire can make a difference but not enough to matter in this case.

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KipD

17 posts in 294 days


#3 posted 03-03-2018 08:20 PM

Thanks- very helpful.

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KipD

17 posts in 294 days


#4 posted 03-05-2018 02:14 AM

Found a nice and simple Siemens Excel calculator at “DA estimated voltage drop calculator xls”. You can input your values for a detailed calculation. Did not post screen shot because, last I checked, Photobucket was wacky. I’ll check again- want to be able to post pictures.

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MrUnix

7046 posts in 2400 days


#5 posted 03-05-2018 02:18 AM

There are a bunch of calculators on-line – most of the major wire manufacturers have them.

Cheers,
Brad

PS: There is no need for photobucket or paying their ransom… you can upload pictures directly to this site.

-- Brad in FL - In Dog I trust... everything else is questionable

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coxhaus

93 posts in 1095 days


#6 posted 03-06-2018 04:46 AM

My old Unisaw has a 3 hp motor and is rated for 16 amps @240v. Weird there is a 3 amp difference between motors.

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KipD

17 posts in 294 days


#7 posted 03-06-2018 10:07 AM


My old Unisaw has a 3 hp motor and is rated for 16 amps @240v. Weird there is a 3 amp difference between motors.

- coxhaus

Yah…. learning about this stuff. I do know that the Rigid 4512 with 1 1/2HP motor is rated at 13 amps @ 115V- so that’s a similar spec. The Leeson motor that comes with my saw and is the same one as shown in the spec sheet I attached, I think is new/current and/or recent design. I hope it’s as good as it’s expensive: cheapest online price $550….. list $1200 (!?).

If ratings are accurately and honestly done, this might mean that my 13A Unisaw motor is more effecient: created 3HP at 13 amps- like miles per gallon with a car. I have made a “Y” cheater cord using two household 115V outlets from opposing service legs to get 230V to test my Unisaw- this will give me an opportunity to measure amps with clamp-on ammeter.. Curious to see what start-up amps are. Then, I will try to put a load on it by cutting some hard wood to get a feel for amps and what “full load” and 3HP is like. My guess is that I won’t want to push it to more that 8 amps.

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