430.53(c)

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thetacon

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I am looking for clarification about how to use this as a compliant install. The Mechanical contractor set the HRV units on the rooftop of the building today. On the spec sheet it showed that it was a single point connection requiring one 50 amp 3 phase ckt. I roughed in a 6-3 nmb to the unit. when I opened up the unit today it had 2- 3 hp blower motors and 7k of strip heat. the two motors are to run continuously and the heat elements are on call when needed. THis unit had the heater contactor and controls in on section and the two blower motors in a second section. they were independent of each other.In the past the units had a terminal where I landed L1 L2 L3 and the rest was taken care within the unit.Is there a compliant way to put them on one ckt or do I need a ckt for each section?

thanks
 
Nameplate data?

Anything pertinent in the manual/instructions?

The preceding bear heavily on doing a compliant installation.
 
there is no paper work with the unit. The name plate Has the MCA at 26 .2 amps for the motors that are sitting the upper section.. the lower section where the heat strips are located show an fla of 25 amps. the mech contractor said it is actually 2 separate units that are combined into one in the field they recommended 2 disconnects and 2 ckts but that is no easy task as the building has already been sheetrocked
 
Call the manufacture and see if there are installation instructions or a name plate available that would cover this installation

Just curious about the NM cable to this unit. Commercial building? Exposed or not?
 
thetacon said:
there is no paper work with the unit. The name plate Has the MCA at 26 .2 amps for the motors that are sitting the upper section.. the lower section where the heat strips are located show an fla of 25 amps. the mech contractor said it is actually 2 separate units that are combined into one in the field they recommended 2 disconnects and 2 ckts but that is no easy task as the building has already been sheetrocked
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If the circuit run is sufficiently sized as a feeder, mount two "disconnecting means" on the unit. Local disconnects are likely required anyway. You can use two fused disconnect switches or a small breaker subpanel. Either way enclosure(s) must be rated for weather exposure. Apply tap rules for the two disconnect method.

It is possible to run both sections off one circuit... but this depends heavily on manufacturer data. If there is an MCA for each section, I don't believe you can supply both with one circuit as the combined rating necessary to supply both sections would likely be greater than both MCA's.
 
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the ckt i have there is large enough it is good for 55 amps . the unit is 5'x5' can i land the home run on a disconnect then in the controller tap to each motor either a manuel starter or a fuse block to provide the overload protection to the 2 motors
 
thetacon said:
the ckt i have there is large enough it is good for 55 amps . the unit is 5'x5' can i land the home run on a disconnect then in the controller tap to each motor either a manuel starter or a fuse block to provide the overload protection to the 2 motors
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While what you suggest may be sufficient, technically, I believe the intent of most Article 430 & 440 requirements is to provide overcurrent, short-circuit protection prior to equipment entry. Additionally, changing internal wiring without manufacturer blessing will likely void listing and warranty.
 
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