Commissioning Tests and Preventive Maintenance on Schneider Low-Voltage Circuit Breakers.

What are low-voltage circuit breakers?

Low-voltage circuit breakers are devices designed to interrupt the electrical current in a circuit under abnormal conditions, most commonly due to overloads or short circuits, as well as under normal conditions, such as a circuit de-energization.

Low-voltage circuit breakers are suitable for circuits with a rated voltage below 1000 V. To meet the protection criteria, circuit breakers must satisfy the following conditions:

The nominal voltage of the circuit breaker must be equal to or greater than the system voltage. If the breaker’s voltage is higher, its interruption capacity is considered based on the system’s nominal voltage.
The circuit breaker’s nominal current capacity must be equal to or greater than the maximum current that may flow through it.
The interruption capacity of the circuit breaker must be equal to or greater than the three-phase or phase-to-ground short-circuit current—whichever has the greater magnitude—at the point of installation.
The circuit breaker’s insulation level must comply with the system’s insulation level.

Low-voltage circuit breakers manufactured by Schneider, which feature Micrologic, STR, or NSX protection units, can have their performance tested using test kits suitable for each model.

Including these tests during system commissioning is essential to verify the proper performance of the equipment under normal load, overload, and short-circuit conditions, including checking whether the operation times align with the designed protection curves.

For testing circuit breakers with Micrologic and STR units, the FFTK 34559 and S33594 test kits are used: