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Old 04-19-2019, 11:33 AM   #1
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Default Motor Feeder Conductor Temperature Rating

I was looking at some cable sizing for an Industrial MCC and i looking at the MCC Details, Allen Bradley 2100 MCC, it says

"MCCs are rated for use with 75 C (167 F) cable. Cable must be sized by using a 75 C (167 F) column in NEC Table 310.15 (B) (16) (NFPA 70-2017). The temperature rating of the lugs is not relevant."

Although that is for NEC, but i am presuming CEC would be the same.

Just searching i ran into the discussion below which seems to suggest that if the motor is Class A, then 90C table is acceptable.

electriciantalk.com/f31/motor-feed-conductor-temperature-rating-82729/

My understanding is that all sizing needs to be done per the 75C table, as that's what the MCC design suggests, but wondering if that is not necessary or covered somehow differently in code.
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Old 04-19-2019, 01:35 PM   #2
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Originally Posted by arbitarytwist View Post
I was looking at some cable sizing for an Industrial MCC and i looking at the MCC Details, Allen Bradley 2100 MCC, it says

"MCCs are rated for use with 75 C (167 F) cable. Cable must be sized by using a 75 C (167 F) column in NEC Table 310.15 (B) (16) (NFPA 70-2017). The temperature rating of the lugs is not relevant."

Although that is for NEC, but i am presuming CEC would be the same.

Just searching i ran into the discussion below which seems to suggest that if the motor is Class A, then 90C table is acceptable.

electriciantalk.com/f31/motor-feed-conductor-temperature-rating-82729/

My understanding is that all sizing needs to be done per the 75C table, as that's what the MCC design suggests, but wondering if that is not necessary or covered somehow differently in code.
Only the first 1.2 meters of conductor connected to the MCC would have to be rated at 75 degrees, not the whole length from MCC to the motor. 4-006(5)

Same goes for the conductor connected to the motor. If the motor is a class “A” motor and 90 degree rated conductors are used, only the fist 1.2 m of conductor connected to the motor is permitted to be rated at 90 degrees. 28-104(2)+(3)

Wiring from junction box to junction box that is not connected to any equipment can have it’s ampacity rated at the temperature rating of the conductor. 4-006 is only for wires connected to equipment.
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Old 04-19-2019, 07:08 PM   #3
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Only the first 1.2 meters of conductor connected to the MCC would have to be rated at 75 degrees, not the whole length from MCC to the motor. 4-006(5)

Same goes for the conductor connected to the motor. If the motor is a class A motor and 90 degree rated conductors are used, only the fist 1.2 m of conductor connected to the motor is permitted to be rated at 90 degrees. 28-104(2)+(3)

Wiring from junction box to junction box that is not connected to any equipment can have its ampacity rated at the temperature rating of the conductor. 4-006 is only for wires connected to equipment.
So in that case its 75C if you go direct from MCC to Motor Class A or not if the MCC is "rated for 75C"
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Old 04-19-2019, 07:41 PM   #4
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So in that case its 75C if you go direct from MCC to Motor Class A or not if the MCC is "rated for 75C"
Yes.
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