Why should the air switch have both overload protection and short circuit protection

Air switch (hereinafter referred to as "air switch", here we specifically refer to the GB10963.1 standard household circuit breaker) protection object is mainly cable, the main question is "why should the air switch set overload protection and short circuit protection" can be extended to "why should the cable set overload protection and short circuit protection at the same time"

1.What is overcurrent?

The loop current that is greater than the rated carrying current of the loop conductor is overcurrent, including overload current and short-circuit current.

2.the cable overload protection

The electrical circuit due to too much electrical equipment or electrical equipment itself overload (such as motor mechanical load is too large) and other reasons, the current value is many times the rated current of the circuit, the result is that the cable operating temperature exceeds the allowable value, the cable insulation accelerated deterioration, shorten the life. For example, for PVC cables, the maximum allowable working temperature for a long time is 70°C, and the allowable transient temperature in the case of short circuit does not exceed 160 ° C.

The cable can withstand a certain overload current for a certain period of time, but the duration should be limited. If the overload current lasts too long, the cable insulation will be damaged, which may eventually cause short circuit fault. Temperature state of the insulation layer of the cable under normal current, overload current, and short circuit current.

Therefore, In the standard value of the circuit breaker product, the circuit breaker is required to be 1.13In, the overload current does not operate within 1 hour (In≤63A}), and when the current is opened at 1.45In, the overload line must be removed within 1 hour. Overload current is allowed to continue for 1 hour to take into account the continuity of the power supply and the cable itself has a certain overload capacity, can not be slightly overloaded line, the circuit breaker will cut off the power, which will affect the normal production and life of residents.

The protection object of the circuit breaker is the cable. Under overload conditions, long-term overload will cause the temperature to rise, resulting in damage to the insulation layer of the cable, and eventually a short circuit fault.

Under short circuit conditions, the temperature will rise in a very short time, if not cut in time, it may cause spontaneous combustion of the insulation layer, so as a protection component of the circuit breaker, both overload protection function, but also need short circuit protection function.

Post time: Sep-25-2023