Multiple wires in Conduit

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delectric123

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I am making an electrical installation consisting of 12 - ventilating fans operating on 240 Volts 3 Phase with each fan motor having a FLA rating of 4.2 A. These fans are all approximately 200 ft. away from the control room. In the control room, the breaker panel is about 10 ft. away from the contactor boxes? The contactor boxes are factory assembled with each box housing 4 contactors with thermal overloads. The boxes are wired for connection to one breaker. Would a 20 amp breaker be permissible?If a 20 amp is allowed, and I?d use 12 AWG wire for going to all the fans, would it be allowed to have all the wires(36 current-carrying conductors) in the same raceway?(PVC conduit)
 
In my opinion:
NEC requires the values in Part XIV Tables be used for most calculations so I will assume you motors are 1HP which would correspond with your 4.2 amps.
Section 430.52 limits the SC-GF protection to 250% in most cases so your maximum breaker for one motor would be a 15 amp breaker if there is no SC-GF protection in your controller cabinet most lilely limiting you to two motors per breaker.
Your conductor ampacity would be required to be 5.25 amps. 36 ccc in one conduit would have a derating factor of .40 so your #12s would be fine, in fact a #14 would be adequate.
 
Section 430.52 gives the maximum rating the overload device can be set. Section 430.53 (C) (4) clarifies my situation. Each motor is protected by a thermal overload on the contacter. 4.2 x 4 = 16.8 i don't think the 80% breaker rule applies to me because these motors will never be under heavy load. my concern was 36 current-carrying conducters..........will those 12 AWG wires be overcurrent-protected from the 20 amp Breaker?
 
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delectric123 said:
Section 430.52 gives the maximum rating the overload device can be set. Section 430.53 (C) (4) clarifies my situation. Each motor is protected by a thermal overload on the contacter. 4.2 x 4 = 16.8 i don't think the 80% breaker rule applies to me because these motors will never be under heavy load. my concern was 36 current-carrying conducters..........will those 12 AWG wires be overcurrent-protected from the 20 amp Breaker?
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What code section would exempt you from the "80%" rule for conductor ampacity or OCPD loading for a regular breaker?

The heaters/thermal overloads provide over current protection, the breaker provides GF-SC protection for the conductors.

Your minimum conductor ampacity is 4.2 x 1.25 + (3*4.2) = 17.45.
 
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that applies to feedersthe motors are after the breaker panel, so they're on branch circuits.NEC dictates that to size overcurrent protection add together 125% FLA of largest motor, plus FLA of others.(1.25 * 4.2) + 4.2 + 4.2 + 4.2 = 17.85
 
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