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Forum topic by MAYTAG posted 04-11-2008 04:12 PM 1084 views 0 times favorited 4 replies Add to Favorites Watch
View MAYTAG's profile


1 post in 3662 days

04-11-2008 04:12 PM

Hello All,

I just acquired a new table saw and planer. I intend on using the old ones for rough planing and ripping in a seperate area of the shop.

The saw is not really an issue, but the planer has a 3HP motor and requires 230V.

In this area of the shop, there is a already a 220 line of 12-2 wire on a 30A breaker. So I have two questions;

Can I use the 12-2 wire and if not, if I feed the line with 10-2, will this be sufficient for the planer on a 30A breaker?

4 replies so far

View GaryK's profile


10262 posts in 3953 days

#1 posted 04-11-2008 05:36 PM

#12 wire would be fine as long you are not more than 60 feet from the breaker.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View ww_kayak's profile


70 posts in 3689 days

#2 posted 04-11-2008 10:15 PM

In most areas I’d say Use 10-2

14 → 15A
12 → 20A
10 → 30A

-- Tom, Central New York

View tenontim's profile


2131 posts in 3709 days

#3 posted 04-12-2008 03:40 AM

Not to mention “code”, if it applies.

View dustmonkey's profile


19 posts in 3610 days

#4 posted 06-03-2008 02:46 AM

Ordinarily to comply with the National Electrical Code (NEC), you cannot have a 30A breaker protecting #12 wire, but motors have different requirements where protection can be higher to prevent breaker tripping during motor start-up. Motors draw approximatel 6-8 times full load current for up to 15 cycles (15/60 = 1/4 second). In order to size wire correctly for a single motor, you must multiply the motor namplate full load amps (FLA) by 125%. You can use the NEC tables if the nameplate does not list FLA. This will give you the minimum circuit amps (MCA). For example; If your MCA was 24A then you would need at least #10 wire. Then you select the next closets wire size that matches (but not smaller). Then you size the motor feeder protection (circuit breaker or fuse). Molded case circuit breakers can be sized up to 250% of the motor FLA. I usually go as high as 175% depending on the motor and its use, since some motors draw more on start-up dpending on their design and use.

For a 3HP 240V single phase moter the NEC lists 8.3A, 1.25×8.3=10.4A, so #12 wire should be fine. 8.3×2.5=20.8A, the code allows the next higher size breaker to be used as long as it does not exceed 400% of the motor FLA (for motors under 100A), since 30A is less than the 400% you are okay with a 30A breaker.

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