What is the current multiplier for a current transformer (CT) rated at 200/5?

The correct answer reflects the relationship between the primary current rating and the secondary current rating of a current transformer (CT). A CT rated at 200/5 means it is designed to take a primary current of 200 amps and convert that down to a secondary current of 5 amps.

To determine the current multiplier, you divide the primary current by the secondary current. In this case, it is calculated as follows:

200 (primary current) ÷ 5 (secondary current) = 40.

This reflects that for every ampere of current that flows through the primary winding, the CT will produce 1/40th of that current in its secondary winding.

This multiplier is crucial in applications such as metering and protection, where it allows devices rated for lower currents to safely measure or react to higher currents in the system. Understanding this relationship helps linemen interpret and utilize readings accurately.