out of the toroid. If they conduct current during a ground fault, the net magnetic effect will be zero
and no current will be seen by the relay.4 Because the secondary current is a true reflection of the
total three-phase primary current, there is no CT error due to any unbalanced primary current. The
CT ratio can be any standard value that will provide the relay current from the available ground
current for adequate pickup. Since there will be no error current, the relay can be an instantaneous
relay set at a low value. Typical relay calculations are shown in the following examples.