If a CT has a current ratio of 500:1 and indicates 67 mA, what is the current in the primary circuit conductor?

To determine the current in the primary circuit conductor when a current transformer (CT) indicates a secondary current of 67 mA with a ratio of 500:1, you multiply the secondary current reading by the CT’s current ratio.

The current ratio of 500:1 means that for every 500 amps flowing in the primary circuit, the CT will output 1 amp in the secondary circuit. To find the primary current, you can set up the calculation as follows:

1. Convert the secondary current from milliamps to amps. Since 67 mA equals 0.067 A (because 1 A = 1000 mA, so you divide 67 by 1000).

2. Use the current ratio to calculate the primary current:

Primary Current (I_primary) = Secondary Current (I_secondary) x Current Ratio

I_primary = 0.067 A x 500

This calculation gives:

I_primary = 33.5 A

Thus, the current in the primary circuit conductor is 33.5 amps. This explanation shows how to approach problems involving current transformers and their ratios, reinforcing the relationship between primary and secondary currents in electrical systems.