2 motors on single overload

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mpieper

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In our planned installation we have a rooftop fan atop of a curb which houses an associated motorized damper. Can the damper motor be powered from the fan's T-leads without requirement for "separate overloads" (NEC 430)?

The fan mfgr's literature does not necessarily show the motor controller and/or overloads in their simplified wiring diagram; however, it does show the 2 motors sharing power from a disconnect. I assume this to be the local disconnect which is provided by the fan manufacturer within the fan housing.

Fan motors are 208V, 3ph, and as large as 5HP. Most are fractional.
Damper motors are 208V, 1ph, "impedance protected" and do not indicate their amp draw. The supplier simply asserts that they draw "milliamps".
There is 1 damper motor per fan motor. Damper & Fan motor operate simultaneously (without any other control or interlock). A combo starter (with adjustable overloads) has been provided for the fan motor. We have requested that the electrical contractor wire the damper motor off of the fan motor's T-leads (that is the conductors between the starter's overload and the fan motor).

I can't disagree with the electrical contractor's interpretation of Article 430 (separate overloads); however, its seems to be industry standard to wire the damper motor from the fan motor starter's T-leads. Is there an NEC basis for wiring damper motors in this way?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
Just an opinion, but it appears to me that 430.32(A)(4) would allow the damper motor to be connected to the "T" leads, but, the reference to 430.32(D)(2) would likely require you to have a lower SC/GF protective device, especially with the larger blower motors, so some type in-line fuse might be in order.
 
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