Branch Circuit for size for motor.

[KP2]

What is thae branch circuit conductor size for a 5 HP, 3 phase, 208 volt motor with a nameplate amperage of 15.3 amps and service factor of 1.15?

I come up with this:
Full Load Current is 16.7 amps
16.7 X 125% = 20.875
Because of the footnote *240.4(D) I feel that a # 12 is no good and I must use a # 10.
I thought that because it is for a motor like mentioned in 240.4(G) the small conductor rule does not apply, but I cant find anything in 430 to support this hunch and feel that a # 10 must be used.

Help if you can
Thanks
Kevin

 

[tom baker]

No, 12 is fine, its ampacity at 75 deg is 25 amps.
You have to read the rest of 240.4
240.4 Protection of Conductors.
Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).
G is what allows a small wire on a big breaker for a motor.

 

[KP2]

Thanks

Thanks

Thanks, I got caught up in the *.

 

[ozark01]

This guy sized his overcurrent and wire large enough not to be bothered with blown fuses. This is for a table saw in a old woodworking shop.

 

[tom baker]

Great picture I use that in one of my classes.
Interesting how what we put in 40 years ago we thought was safe, but compare it to todays products!
A common error is to install the largest size fuse possible in the clips. Now that black tape is special.

 

[ozark01]

This building originally had a 3-phase 240 delta service and it was converted to a 120/240 volt single phase. They used the same disconnects and moved a few wires to get neutrals where they needed them. It was quite a messy electricial system. The buyers (Meal-on-Wheels) were going to make the builidng into a kitchen.