Conductors Feeding the Branch Circuit

[fifty60]

Inside an industrial machine I have single equipment circuit breaker that feeds multiple branch circuits. Do the conductors between the main equipment circuit breaker and the branch circuits need to be sized to the Main OCPD or can they be sized to the Branch OCPD?

For example, I have a machine that the main power conductors land into a 60A circuit breaker. The conductors a then from the 60A breaker out to four 10 A breakers. I know the conductors coming into the 60A breaker have to be sized for the 60A breaker (6AWG), but do the conductors going from the 60A breaker to the 60A breaker have to be 6AWG, or can they be sized to the branch OCPD?

 

[Dennis Alwon]

Are you saying that the machine doesn't call for a 60 amp breaker from the panel? I am confused. If the minimum circuit ampacity for the machine is 50 amps then the wire and breaker feeding the machine can be sized for the 50 amp load.

 

[dkidd]

Inside an industrial machine I have single equipment circuit breaker that feeds multiple branch circuits. Do the conductors between the main equipment circuit breaker and the branch circuits need to be sized to the Main OCPD or can they be sized to the Branch OCPD?

For example, I have a machine that the main power conductors land into a 60A circuit breaker. The conductors a then from the 60A breaker out to four 10 A breakers. I know the conductors coming into the 60A breaker have to be sized for the 60A breaker (6AWG), but do the conductors going from the 60A breaker to the 60A breaker have to be 6AWG, or can they be sized to the branch OCPD?

I would treat them like taps and size for the 10A breakers. I don't know what any industrial control panel standards like UL 508 would say.

 

[Sahib]

Also, if possible, bring 60A and 10A breakers close together if you are field wiring the equipment.

 

[fifty60]

The Machine has a molded case circuit breaker attached to its electrical sub panel. The main power wires feeding the panel are landed directly into this circuit breaker. The amp rating of the circuit breaker is 60A. The ampacity of the wires feeding the breaker is 65A (6AWG).

I have the wires coming out of the circuit breaker land inside a distribution block that has 1 conductor hole for each incoming line, and 4 corresponding holes for load connections.

I consider the 60A breaker the "machine disconnect". This disconnect is feeding 4 other 10A breakers. The load side of the distribution blocks described above connect directly each one of the 10A breakers. The conductors I am concerned with are the conductors between the 60A "Machine Disconnect" and each one of the 10A branches.

I know in Germany, they want you to only make conductor size changes at OCPD's. UL508 doesn't directly address this, but does say that the wire ampacity should be sufficient for the load. NFPA 70 talks about this indirectly when it talks about Feeder's, Taps, and Branch circuits. But i do not see it addressed specifically.

I think I should treat each one of the conductors coming out of the distribution block as "Feeder Taps", and as long as they are 10 feet or less I can size them to the branch circuit breaker they are connected to......

 

[raider1]

UL 508A has requirements for feeder taps that mirror 240.21(B).

I would treat the conductors like feeder taps and size them as such.

Chris