OCPD Requirement

[Electriman]

Greetings,

When we are dealing with power electronic equipment i.e. VFDs, UPSs, DC chargers, do we need to specify a circuit breaker as OCPD for output cable protection considering that these devices usually have over current protection imbedded in their control algorithms? What is the position of the NEC in this regard?

Thanks

 

[retirede]

The NEC basically stops at the connection of the utilization equipment.

 

[Jraef]

The NEC will require that you follow manufacturer's instructions, which for most reputable manufacturers, includes what OCPD must be used for the device. Usually what they give you is a MAXIMUM size, but also a specific type of breaker, fuse etc. Then because you also must pay attention to the SCCR now, you may find there are restrictions on what OCPD can be used and maintain a reasonable SCCR level, usually being fuses. It's worth paying close attention to because inspectors are getting educated on what to look for now.