VFD package disconnect means

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skeshesh

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Los Angeles, Ca
We're designing an HVAC upgrade to a facility. Mechanical engineer is using 4 new air handling units which consist of a supply fan and a return fan (10hp, 5hp respectively). The package manufacturer will provide circuit breakers for each individual VFD and the control scheme allows for only one motor (fan) to operate at a given time. I was wondering if it's required per code to provide an external disconnect for the entire package or if the circuit breakers can be used as the disconnect means.
 
My first concern would be if their breakers meet the following:
440.14 Location.
Disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment. The disconnecting means shall be permitted to be installed on or within the air-conditioning or refrigerating equipment.
 
Yes I believe that req. is met. I've also sized conductors req. per 430.24. Also let me add that the units are fed from an existing MCC (600A horiz./300A vert.). The new molded case CBs that will be installed in said MCC could be used as disconnect means but they're definitly not very close to the units; units will be on the roof while the MCC is in an electrical room, and while the electrical room has a ladder leading directly to the roof, it is certainly not "in sight" if you're standing next to motors.
 
You need to comply with 430.102(B) and unless the installation meets the requirements of the exception, you will have to provide a disconnect within sight of the motors.
 
I gather you have a feeder that goes out to 8 VFDs that each have their own MCCB.

The feeder disconnect is in the existing MCC. It does not appear to qualify as the required disconnect for any of the motors.

If the MCCB for each VFD meets the requirements as a disconnecting means location wise (within 50 feet, readily accessible, etc.) I don't see that you need anything else.
 
VFD disco

VFD disco

If the MCCB for each VFD meets the requirements as a disconnecting means location wise (within 50 feet, readily accessible, etc.) I don't see that you need anything else.
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Yea that's pretty much what I'm getting at but I concerned if, based on the fact that only one motor is running at a given time, I am satisfying 430.102(B). (as don pointed out). Also, I think I could use exception 430.102(B)(b) as this is an industrial military building and they have trained staff on base 24/7. At the same time, I've seen some really shady work done by military maint. guys so I don't know if its safe to assume the exception.

At the end of the day, I think I might toss in a disconnect anyway, since these guys really don't care that much about the budget. Still I like learn the proper code application for my own knowledge.
 
I would appear that you could use the circuit breakers as the disconnecting means as per Art.430.102. Exception (Lockable) and (B). Ref: 2008 Code Cycle
 
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