CTs on line side of main disconnect in MCC
CTs on line side of main disconnect in MCC
(OP)
I'm looking for opinions or even standards I am unaware of on this issue.
I am being asked to move the CTs for a power monitor to the LINE side of a 600A main fused disconnect switch of an MCC. This is a non standard configuration for us and requires significant re-engineering, something I'd like to avoid (not because I'm lazy but because the customer wants it FAST). Are there any reasons I'm not thinking of for NOT doing this? I was thinking safety, but if the disconnect was open (so the door could open), there could not be any current flowing so no output potential on the CTs. So this issue doesn't hold much water. I also know that utility CTs are generally on the line side of a service disconnect, so it's not unheard of. Anything else? Or am I all wet and we should develop a standard configuration this way because lots of people are going to ask for it? To that issue, we have been making MCCs for 50+ years, this has apparently never come up before.
I am being asked to move the CTs for a power monitor to the LINE side of a 600A main fused disconnect switch of an MCC. This is a non standard configuration for us and requires significant re-engineering, something I'd like to avoid (not because I'm lazy but because the customer wants it FAST). Are there any reasons I'm not thinking of for NOT doing this? I was thinking safety, but if the disconnect was open (so the door could open), there could not be any current flowing so no output potential on the CTs. So this issue doesn't hold much water. I also know that utility CTs are generally on the line side of a service disconnect, so it's not unheard of. Anything else? Or am I all wet and we should develop a standard configuration this way because lots of people are going to ask for it? To that issue, we have been making MCCs for 50+ years, this has apparently never come up before.
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RE: CTs on line side of main disconnect in MCC
Current will be the same on the line or load side, except for a fault in the switch so there's no technical reason either side would not work.
I would push the safety during testing issue.
Good luck.
RE: CTs on line side of main disconnect in MCC
But for a power monitor I'm not sure what he gains by changing location.
Taking a contrary position to rcwilson's comment about de-energised working on the CT, if the bus is dual-fed then it may be possible to take an incomer out of service for maintenance more easily than taking the bus down.
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RE: CTs on line side of main disconnect in MCC
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies