Harris Institute of Technical Training

Now, to address the mis-wired installation you described and what that metering error was:

1.) Va-n and Vc-n are still the two voltages connected to the meter potential coils.

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

3.) The ‘c’ phase CT would have been 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’ phase to non-polarity ‘n’ on the potential coil.)

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

4b.) The ‘a’ phase CT would have been wired to the second meter stator current coil with Vc-n voltage on the stator potential coil (the non-polarity of ‘a’ phase CT current matched with the polarity voltage of ‘c’ to non-polarity ‘n’ on the potential coil). Now ‘a’ phase CT current is wired so that it goes backwards through each of the two meter current coils. (See vector diagram for reference).