att: metering experts

[kooman]

guys i need a metering expert, i was sent out to check a meter installation for accuracy today and need help. the service is 277/480, it has 3-200:5 ct's, also has 3 voltage trans for the old 120 volt meter that is there and they are 2.4:1 ratio (288 to 120). my question is on the multiplier, the 200:5 ct's would be a 40 mult. but then do you multiply that times the 2.4 to make it a 96 mult? (that is what the office is billing) this is my understanding but want to make sure. thanks

[Trbl639]

Not an expert, but I believe that is right!!

Electric Lady will know for sure, she is the Resident Metering Expert!!! She is a Pro there!!

[Boomer gone soft]

That sure sounds right to me also.

[electriklady]

How'd I miss this one?

yes.....the multiplier is a product of the pt and ct ratios.

Since I became qualified to work transformer rated(last year) I have have limited contact with pts..........unless they are an old install.........mainly primary metering as we dont use pts anymore except on primary metering.....on occasion I find an "oldie goldy" with both cts and pts......if we have to rewire the cts(broken wires,cracked insulation) we remove the pts and rewire the cts......otherwise we just "let sleeping dogs lie."

[Electriceel]

You are exactly right for the multiplier. CT ratio times PT ratio equals meter multiplier.
We used to allow 480 volts in the meter socket, I realize the new meters are multi-range 120/480. We started having trouble with failed meters, went back and installed PT's and have eliminated basically all of our problems from spikes.
Also a lot safer, think about it, 480 volts in a socket with those close quarters, 120 sounds and is a lot safer.