Protection and metering CT question

[elecsun]

Recently we recieved one medium voltage feeder panel(13.8kV,60Hz system) where Common protection class Ct's used for protection relay(multifunction relay which has the facility to read currents,voltage etc)and ammeter with selector switch.Does ANSI/IEEE stanadrd allow such panel wiring?Is there any need to install ammeter with selector switch when modern multifunction relays can be used for measurements purpose also?!!

 

[dpc]

It's done all the time. There is nothing in ANSI or IEEE to preclude this.

But there can be times when an analog ammeter is handy to have, so there is nothing wrong with having both.

But if you're concerned about revenue or billing metering, the relay and the protection CTs will not be accurate enough to satisfy the requirements for revenue metering in most cases.