Paralleling Current Transformers

Current Transformers Object

This page discusses the issues of using current transformers (CTs) in parallel. Circuits with multiple conductors (common on high current circuits): Measuring Parallel Conductors. To add the power and energy readings of multiple branch circuits and measure them with one WattNode.

When paralleling CTs, the effective CT rated amps CtAmps is equivalent to the sum of the individual CT rated amps. So if you parallel two 100A CTs, the effective CtAmps is 200A. If you parallel three 50A CTs, the effective CtAmps is 150A.

Current Transformers

All parallel CTs must be exactly the same model: same amp rating, same frame size, and same style. Different CT models have different internal burden resistors, so combining them in parallel will not work correctly.

Add one set of CTs at a time, checking the WattNode output each time, to ensure none of the CTs are reversed or incorrectly phased.