First of all, the simplest difference between them is: 1P circuit breaker can only disconnect one line alone, 2P circuit breaker can disconnect two lines at the same time, and 3P circuit breaker can open three lines at the same time.
Infer their application:
1P circuit breakers are often used in occasions where only one live wire needs to be disconnected.
For example, 1P circuit breaker is used to control the live wire of the lighting circuit.
2P circuit breakers are often used in occasions where two wires need to be disconnected at the same time.
Such as single-phase 220V socket, single-phase 380V welding machine, etc.
3P circuit breakers are often used where three wires need to be disconnected at the same time.
Because the ground wire does not need to pass through the switch, the 3P circuit breaker is mainly used for three-phase electrical equipment.
Such as three-phase motors, three-phase welders, three-phase ovens, etc.
4P circuit breakers are often used in occasions where four wires need to be disconnected at the same time, mainly for low-voltage power distribution lines. Such as floor master switch, workshop master switch, three-phase five-wire electrical equipment master switch, etc.