Multiple Air Compressors. Branch circuit or feeder calculation?

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Nitty

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I am looking into a project that involves wiring four air compressors, specs show "Input Package Amps (max)" at 310 amps. This is a large industrial facility with multiple services. The customer wants to place the four ACs next to under utilized service equipment. This service equipment is rated at 2000 amps. Question - Since the compressors would be placed with-in 50 feet of the service distribution gear and the circuit breaker protecting each unit would serve as the disconnecting means, would the circuit from the breaker to the compressor be seen as a individual branch circuit or a feeder? According to the definitions it appears to be a ind. branch circuit ( just seems a little odd to call a 400 amp circuit a branch circuit).The reason for asking this is the NEC treats branch circuits different from feeders when determining load calculations. If it is a feeder I would use 220-50, 430-25 to determine load applied to service, equaling (310x4) 1240 amps. No mention of 125% of largest load.If they are considered branch circuits then I have to take 125% of each unit to determine load on the service. (310x1.25) x 4 = 1550The difference is substantial when applying this calculation to the parameters of 220.87.
 

Smart $

Esteemed Member
Location
Ohio
A/C compressors are a special-purpose branch circuit. See 210.2 and its Table and referenced Article 440 sections. If the "Input Package Amps (max)" at 310 amps is actually an MCA rating, it already includes 125% for the motor compressor.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
A/C compressors are a special-purpose branch circuit. See 210.2 and its Table and referenced Article 440 sections. If the "Input Package Amps (max)" at 310 amps is actually an MCA rating, it already includes 125% for the motor compressor.

It sounds like these are skid mounted AIR compressors, not air conditioning compressors.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
With those size compressors and that size service you might want to take a close look at your available fault current and equipment ratings. I have seen some of those where the manufacturer calls for current-limiting fuses ahead of their equipment.
 
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