Long time delay (tr) sets length of time that the circuit breaker will carry a sustained overload before tripping. The delay bands are labeled in seconds of over current at six times the ampere rating. Long-time delay is an inverse time characteristic in that the tripping time decreases as the current increases.

What is IR in breaker?

1. Continuous Amps (Ir) Continuous Amps (Ir) varies the level of current the circuit breaker will carry without tripping. Ir is a percentage of the circuit breaker’s nominal rating (In). … For example, a 1000 amp breaker can be changed from 1000 amps to 800 amps by adjusting the breaker continuous amps setting to 80%.

What is io on Mccb?

‘Io’ is the course setting for the ‘long time’ protection threshold. ‘Ir’ is the fine setting for the long time protecton. You work out you overload protection using In x Io x Ir. Isd is the threshold of the short time pickup.