60-100 words

[1]         How does a magnetic relay operate?

Magnetic relay overloads are of the solenoid type, consisting of an iron plunger surrounded by a coil, one for each phase protected. The coil carries line current, or a proportion of line current if transformers are used. At a predetermined value, the plunger is attracted to the centre of the coil and a pushrod activates a trip bar which opens an auxiliary contact in the operating circuit and activates a mechanical latch.

[2]        What are the four fault ratings of a circuit breaker?

The four fault ratings of a circuit breaker are;

The symmetrical breaking current; the rms value of the AC component of the breaking current.

The asymmetrical breaking current; the rms value of the total breaking current which includes both AC and the DC components.

The making current; the peak value of maximum current loop, including the DC component in any pole during the first cycle of current when the circuit is closed.