Multiple-Motors per feeder

[Keri_WW]

Once and for all I want to make sure I am doing this correctly per NEC 430/440! Please see the attached CAD photo. I have a grouping of 4 exhaust fans on a remote section of the roof, where it would be somewhat of a waste to run separate feeds to each. So it is my intent to power them from one feed to a wireway. The motors are (1) 1.5 HP and (3) 1 HP. I will give 2 examples at different voltages just to be sure:

480V
3A * 1.25 + 2.1 + 2.1 + 2.1 = 10A
Minimum feeder size #12
MOCP (Panel Breaker) - 10A * 250% = 25A

208V
6.9A * 1.25 + 4.8 + 4.8 + 4.8 = 23A
Minimum feeder size #10
MOCP (Panel Breaker) - 23A * 250% = 60A

The real questions I have are as follows:
1) Did I size the breaker feeding the wireway correctly?
2) If the disconnects are fused, will that suffice for motor overload protection?
3) If motor overload is provided by default from the manufacturer, do those disconnects need to be fused?
4) Is this the best way to set up a system? And did I miss anything??

Thanks so much!
Keri

 

[augie47]

Actually per 430.62, your feeder SC/GF protection is determined by the sum of the largest branch circuit SCGF protection plus the sum of the FLA for the other loads.
In your situation #1 3 x 2.5 + 3 x 2.1 = 13.8 next size = 15
#2 6.9 x 2.5 + 3 x 4.8 = 32 next size= 35

Fuses are an acceptable overload protection device per 430.32 although some type of separate overload device is more often used. How are these units started ? by a contactor or just a switch ?

Not to rain on your parade and I do not know all the specifics, but a circuit breaker (or breakers) suppling (4) manual motor starers (or magnetic if control is needed) with 4 sets of conductors in one conduit might be to a greater cost advantage than the "common feeder" in this situation.

 

[Keri_WW]

The big problem with going the other way (feeding them all individually) is that I would then need to find a whole lot of panel space! I'm talking 10 fans, 3-poles each!

These fans are controlled via a DDC panel which turns them on based on a set schedule of occupancy; so basically they will run continuously for a set amount of hours out of the day.

Edit: I should also add that it is the mechanical contractor's responsibility to provide the starter/disconnects on this job, so I was attempting to make it as easy as possible for my EC.

 

[augie47]

In that case your plan may be the best. I might add, if you are going 480, the 15 amp max breaker would still allow you a number of fans per breaker
which could save you a little bit of panel space.