Equipment Overcurrent Protection

[overkill94]

Regarding overcurrent protection for an individual piece of equipment (i.e. CNC lathe), NEC section 409.21 is a bit confusing for me.

I've called out fuses provided with a piece of equipment as being oversized (i.e. 200 Amp fuses provided with a piece of equipment rated at 80 Amps and the upstream circuit breaker also being 200 Amps) and gotten some pushback from the manufacturer. They maintain that as long as each branch circuit is properly protected then it doesn't really matter what the main overcurrent protection is as long as it properly protects the incoming wiring (which makes sense to me).

Am I misreading this section or should a calculation be made for every piece of equipment as far as overcurrent protection is concerned?

 

[GoldDigger]

A piece of equipment containing one or more motors will almost always contain it's own overLOAD protection for each motor.
Given that low level (up to several times normal maybe) overcurrent protection is provided that way, the upstream branch breaker only needs to provide short circuit and ground fault protection for the wires.
The manufacturer will specify the maximum size of that external OCPD. If two or more such machines up on one branch circuit and the branch breaker ends up larger than the max size for any of the machines, those machines will need their own fused disconnect or other OCPD.
If the situation involves only motors rather than motor-containing machines, then there is a specific NEC rule for such circuits.

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[overkill94]

A piece of equipment containing one or more motors will almost always contain it's own overLOAD protection for each motor.
Given that low level (up to several times normal maybe) overcurrent protection is provided that way, the upstream branch breaker only needs to provide short circuit and ground fault protection for the wires.
The manufacturer will specify the maximum size of that external OCPD. If two or more such machines up on one branch circuit and the branch breaker ends up larger than the max size for any of the machines, those machines will need their own fused disconnect or other OCPD.
If the situation involves only motors rather than motor-containing machines, then there is a specific NEC rule for such circuits.

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This is a conveyor system which consists mostly of motors but also some transformers and power supplies for various controls. Each motor has its own combination overload as well as fuses for each handful of motors but the main overcurrent protection is much larger than the combined load for the unit.