How many current transformers are used in one distribution box

A distribution box can have one, two, or three current transformers, depending on the measurement and protection requirements of the system.

Typical Configurations

One Current Transformer:

• Used to measure current from a single line or a single-phase system.
• Can measure a three-phase balanced line because the currents in each phase are nearly equal.
• Commonly applied for expanding the range of single-phase meters, measuring single-phase current, or sampling for reactive power controllers . Two Current Transformers:
• If installed on the same phase bus, functions similarly to a single CT.
• If installed on two different phase buses, used to measure three-phase currents in balanced or unbalanced systems. The third phase current can be calculated from the other two, enabling monitoring and protection of the entire system . Three Current Transformers:
• Used for accurate measurement of three-phase balanced or unbalanced currents.
• Can be connected to three-phase meters for precise energy measurement.
• Often used with thermal relays to expand their range and enhance system safety and reliability .

Additional Notes

Some distribution boxes may contain more than three CTs (up to five or six) to serve multiple measurement or protection functions simultaneously, such as monitoring different circuits or providing signals to multiple devices . The exact number depends on the system design, load configuration, and the need for metering, protection, and control. In summary, the number of current transformers in a distribution box is not fixed; it ranges from one to three for standard applications, with additional CTs added for more complex monitoring or protection requirements.