Harris Institute of Technical Training

1.) A correctly wired 5S meter installed on a 4 wire 277/480 circuit with 3 CTs would have the following wiring connection with Va-n and Vc-n being the two voltages connected to the meter potential coils.

2.) The ‘a’ phase CT would be wired to the first meter stator current coil with Va-n voltage on the stator potential coil (polarity of ‘a’ phase CT current matched with the polarity voltage of ‘a’ to non-polarity ‘n’ on the potential coil.)

3.) The ‘c’ phase CT would be wired to the second meter stator current coil with Vc-n voltage on the stator potential coil (polarity of ‘c’ phase CT current matched with the polarity voltage of ‘c’ to non-polarity ‘n’ on the potential coil.)

4.) The ‘b’ phase CT is connected to both meter stator current coils:

4a.) One would be wired to the first meter stator current coil with Va-n voltage on the stator potential coil (the non-polarity of ‘b’ phase CT current matched with the polarity voltage of ‘a’ phase to non-polarity ‘n’ on the potential coil).

4b.) The second would be wired to the other meter stator current coil with Vc-n voltage on the stator potential coil (the non-polarity of ‘b’ phase CT current matched with the polarity voltage of ‘c’ phase to non-polarity ‘n’ on the potential coil). [Note: ‘b’ phase CT current is wired so that it goes backwards through each of the two meter current coils].

This correctly wired 5S meter on a 4 wire WYE service will measure all connected loads to an accuracy that is viewed correct by industry standards. (See vector diagram for reference).