Using utility breaker for arc flash protection 1

[PowerDawg]

I represent a utility that serves a chip mill. The chip mill’s MCC room is served by a 1500 kVA, 4160/480V transformer. The MCC room has no main disconnect, just individual disconnects serving various equipment. The chip mill is asking us if they can install a protection relay in their MCC room and use it to trip our substation breaker due to arc flash protection concerns. The chip mill is the only customer on that breaker. This seems to be the cheapest way to protect their employees from arc flash since they do not have a single source main breaker in their MCC room. I, however, have concerns about them relying on our station breaker for their protection. It seems to me that I would be putting our company at a liability risk by allowing the chip mill to trip our breaker should something go wrong and our breaker fail to operate. Is it reasonable for them to ask to trip our breaker or should I just tell them they will have to install their own main breaker to use for their own protection?

 

[PowerDawg]

Since we have been serving the load (since 1996), the plant calls us when they have a shut down and we physically remove the underground cable from our bus to give them an air gap to work behind in doing their maintenance.

 

[VTer]

I am not sure who owns the transformer and how the service is set up but I would assume that at least one article of the local/national electrical code will mandate that your customer has a main OCPD, being their main service disconnect or secondary transformer overload protection. The first requirement is to meet the electrical code, everything else comes after. Advise them to investigate that first. If the main OCPD is required then there are multiple options to allow for AF reduction in the MCC.

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