Let's analyze the type of tripping curve.

1. A-type tripping curve: magnetic tripping current is (2-3) In, suitable for protection of semiconductor electronic circuits, with small power supply transformer measuring circuit or line length and low current system.
2. B-type tripping curve: magnetic tripping current is (3-5) In, suitable for pure resistance load and low-voltage lighting circuit, often used to protect household distribution system, household appliances and personal safety protection.
3. C-type tripping curve: magnetic tripping current is (5-10) In, suitable for inductive load and high-inductive lighting circuit, often used to protect distribution lines and lighting lines with high turn-on current.
4. D-type tripping curve: magnetic tripping current is (10-20) In, suitable for high inductive load and large impulse current system, often used to protect equipment with high impulse current, such as transformers, solenoid valves.

The use range of miniature circuit breakers with different tripping curves is:
A characteristic: 2 times rated current, seldom used, generally used for semiconductor protection;
B characteristic: 2~3 times rated current, generally used for the two circuit protection of transformer side.
Characteristic C: 5 ~ 10 times rated current, which is the most commonly used in light-duty places, commonly used for building lighting sockets, power distribution panels and so on;
D characteristic: 10-20 times rated current, can be used in heavy-load starting place, can avoid the instantaneous current after starting equipment caused by excessive switching unnecessary overload tripping, generally used for power distribution., small power motor start.

Maintenance electricians must know the type and scope of application of household circuit breaker, in order to choose the most appropriate small circuit breakers in daily power maintenance work, equipment and lines can also be more safe operation.

C characteristic of household circuit breaker is suitable for line protection of inductive load and high inductive illumination system; D characteristic of circuit breaker is suitable for protection of power supply and distribution lines with high inductive load and large impulse current; the biggest difference between them is the ability to resist impulse current.

The difference between C-type and D-type release is that their instantaneous release current is different (i.e. multiple of rated current Ie), so the choice of C-type release or D-type release depends on the type and nature of the load.

C characteristic of household circuit breaker is suitable for line protection of inductive load and high inductive illumination system; D characteristic of circuit breaker is suitable for protection of power supply and distribution lines with high inductive load and large impulse current; the biggest difference between them is the ability to resist impulse current. The starting impulse current of the motor effectively protects the equipment and circuit of this stage under the effective protection of the D-type 63 Amp MCB, and it is no longer important whether the D-characteristic circuit breaker of the upper stage is D-characteristic or C-characteristic, unless the type of the D-characteristic circuit breaker of this stage is too large, the upper stage circuit breaker acts before it in the short circuit state.

According to the national standard, the tripping current of qualified D-type 63 Amp MCB should be 10-14 times of rated current, and the tripping current of C-type circuit breaker should be 5-10 times of rated current. Under reasonable circumstances, type C is generally suitable for lighting lines, and D is suitable for industry.

63 Amp MCB used for motor startup should be type D, type C for distribution control and lighting, type D for short-circuit segment multiple larger than type C, such as rated 32A switch, D short-circuit segment capacity is about 7-10 times rated, C is about 4-7 times.

Popularly speaking, C is suitable for lighting, and D is suitable for power.