Don't Reverse the Polarity: A Guide to Wiring FLEX-CORE® Current Transformers

So, you've purchased one or more FLEX-CORE® current transformers, connected them to a power source and a meter, but the output isn't what you expected.   If you've read our latest article Prevent Polarity Reversal in Current Transformers, you may have realized the mistake, the wiring is reversed. Below we describe how to identify and correctly wire a FLEX-CORE® current transformer.

Our model FCL split-core current transformers have an arrow that indicates the direction of the current flow "→ This Side To Load," and with this given orientation, the X1 terminal (black lead) is the positive side. As a bonus, the FCL current transformers have engraved markings of the H1, which faces the line (source).

While the FCL series current transformers have a black lead wire designated as X1 or positive, the other current transformers with lead wires like 2RL, 5ARL, 7RL series of solid-core, and the 615 and 616 split-core series current transformers have the white lead wire as the X1.

Current transformers have subtractive polarities with the H1 and X1 markings on the same side of the current transformers, typically the H1 on the left side and X1 on the right side when facing the current transformer.

When facing the H1/P1 markings of the JAK-0C and JAK-0S current transformers, the X1 polarity mark is on the left side of the secondary terminal connections, which one can find on the top.

The medium voltage bus bar type of current transformers like the CTWH3-60-T50, JKM-3C, and JKM-5C have different placements of the H1-H2 and X1-X2 markings.

The above illustrations are the typical arrangement of the H1-H2 and X1-X2 polarity markings for current transformers. Other current transformers like the auxiliary and summation current transformers follow the same polarity marking conventions, but the placements may be different.

While correct polarity connections of the current transformers are essential for accurate readings of a metering device, it is critical to have the correct polarities installed for relay protection applications, because incorrect connections cause incorrect operation of the protection relays during fault conditions, and that could have catastrophic consequences to equipment and safety of personnel.

If you're still having problems with inaccurate meter readings, please give us a call (614) 889-6152, our experienced support team can help you diagnose the problem.

Split-Core Current Transformers