Why Current Transformers cannot be connected in parallel

Answer Posted / mark fisher

Current transformers should be connected in series to
provide accurate signals for relaying or metering.

A CT has a very low resistance in the secondary winding.
Therefore, connecting two CT's in series does not
significantly alter the resistance of the circuit (i.e.
.0001 ohm + .0001 ohm = .0002 ohm). The voltage drop caused
by the addition of a second CT to the circuit is negligible.
Connecting two independent CT's in series to obtain a "Net
Current" value in a Breaker-and-a-Half configuration is
quite common.

However, connecting two CT's in parallel will result in the
effective resistance of the circuit being significantly
lower than the resistance of either individual CT (i.e.
.0001 ohm // .0001 ohm = .00005 ohm) and will cause the
voltage to be significantly higher (4X) than with a single
CT.

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