Using utility breaker for arc flash protection
Using utility breaker for arc flash protection
(OP)
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?






RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
Even if they install their own main breaker, someone working on or around the main breaker will still be dependent on the utility's primary side device for protection - that is just the nature of services.
But I agree that the customer should install their own main breaker and make that the new service disconnect - preferably remote from the existing main board. Reliance on transfer tripping of a utility-side breaker creates concerns on both sides of the meter. We have also had industrial customer install their own primary protection (reclosers), after buying the transformer from the utility. They are using transfer trip on these reclosers for arc-flash reduction.
RE: Using utility breaker for arc flash protection
We generally have more confidence that utility equipment will operate properly than customer gear. We used to allow customers to own the overcurrent protection device, but changed practices after discovering a customer had removed the batteries from a switchgear lineup. We generally allow customer to provide a trip signal to our breaker.
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
So for this case, the substation breaker feeds directly to the customers 1500kVA txf? Seems odd that there are no primary fuses on transformer and this is a relatively small transformer in the big power world.
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
It would (hopefully) trip the upstream breaker, but the arc would be gone by that point. Things could get a little exciting if the upstream breaker failed to clear and fault clearance was by backup protection - not sure I like the idea but offering it to provoke discussion. Has anyone used these and had one operate 'for real'?
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
If the fuse were defective, they the liability should go to the fuse manufacturer. If the fuse were pre-damaged, then the liability should go to the customer.
I think we would do that if a customer asked. If you know someone on our board, we might do a lot more. But a transfer trip would be a NO.
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
Would the utility be willing to confirm by measurement that there is no voltage on the high side of the transformer? If the transformer is the only possible source to the switchgear, this may be satisfactory.
RE: Using utility breaker for arc flash protection
RE: Using utility breaker for arc flash protection
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