Wire Size

[Alwayslearningelec]

I know I'm sure I've asked this before, shame on me.

So if the breaker is 150A but the combo starter at the exhaust fan is 200A and fan HP is 60HP at 480v. what is the order/ process of sizing.

I don't see a FLA in the EF schedule but I believe you start by calculating the motor load(amps), then you size the OCPD? But there are two, the starter and the breaker.

The wire should be sized to the 200A starter/disco or 150A breaker?

 

[d0nut]

Answer C: None of the above. 96.25A.

It should be sized to the MCA, which is based on the motor's FLA. Motor circuits are unique in that the upstream overcurrent protection is only required to provide short circuit protection and needs to be sized to allow the motor to start. The circuit's overload protection is provided separately.

 

[steve66]

For motors, I always use my Square D slide rule data calculator. Many of the supply houses gave them away, and you can still find them on ebay. (The back side has 3 phase motors.)

There is also an online version:

Motor Data Calculator | Schneider Electric

d2g0qnfxuxm8zr.cloudfront.net

 

[tjdilly]

Like D0nut says.

60HP motor is 77FLA per table 430.250.

Conductors are sized at 125% (or higher) of the FLA. So, conductors must exceed 96.25A rated.
Breakers are sized at 250% (or lower) of the FLA. NEC 430.52. So, breaker must not exceed 192.5A, use table 430.6 which is 175A. 150A breaker is more than acceptable.

 

[augie47]

In your case the 200 amp breaker is serving more as a disconnect with the 150 providing SCGF protection. As noted the conductor ampacity must be 96 or greater

 

[infinity]

The conductors are sizes according to the table FLC not FLA. Next standard size up rule can also be used.

 

[Dsg319]

name plate HP to go to FLC in NEC and size SCGF.

And motor FLA for overloads.

 

[Jraef]

For motors, I always use my Square D slide rule data calculator. Many of the supply houses gave them away, and you can still find them on ebay. (The back side has 3 phase motors.)

There is also an online version:

Motor Data Calculator | Schneider Electric

d2g0qnfxuxm8zr.cloudfront.net

View attachment 2580335

I miss those, they are hard to come by now. At one time I owned one from every manufacturer I had to deal with, including Clark Control and Arrow Hart. The only ones I can find now are AB, Sq.D and Siemens/Furnas. No idea what happened to the rest, but likely got swept up in one of my wife’s “junk purge” events…