Basler Electric BE1-11t - Manual (Page 225)

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On occasion, however, protection engineers will encounter situations where CT polarity is reversed for a
specific application. That is, non-polarity of the CT secondary will be in phase with the primary current
flow (Figure 168). For example, a transformer differential CT from a breaker with a different polarity
convention such as low voltage switchgear, or a bus differential CT taken from the low side of a
transformer.
Orientation of CT polarity relative to primary current flow establishes the secondary CT terminal that
should be connected to polarity of the BE1-11t.
Figure 166. Standard CT Polarity
Figure 167. Current Transformer Action
BE1-11t Terminals and Connectors