SPD Specific Disconnector (SSD), a SPD special backup protection device of low-voltage power system can withstand the expected surge current of the protected SPD, and can disconnect the device that passes through the power current due to the SPD fault, and has the characteristics of small power current action, also known as SCB.

In general, the backup protection of SPD normally uses fuse or circuit breaker. However, since the surge withstand capacity of fuse and circuit breaker is positively related to the rated current value, it means that if they want to pass the surge test, their rated current value needs to be relatively large. For example, if they pass the tests of 20 kA (In) and 40 kA (Imax), the fuse needs 125 A gL/gG; the circuit breaker needs 63 A-100 A, and the action current of 125 A fuse is up to 625 A within 5 s, which is almost the same value for the circuit breaker meeting the same surge test. This characteristic leads to a blind area for the backup protection of fuses and circuit breakers for SPD. The typical situation is that the capacity of the power system is small, in case of short circuit, the fuse of SPD will not act, so SPD will catch fire quickly. Most SPD fires are caused by this mismatch, and the backup protection does not act.

The characteristic of SSD is that it can pass the surge test matching with SPD. At the same time, it can be triggered by a small power current, generally around 3 A, which is also to ensure that the protection can be started before the SPD catches fire. SSD has the characteristics of high surge withstanding capability, small power current start-up, slim size, high sensitivity and strong breaking capacity.

PTG SSD could perfectly co-operate with PTG SPD, thus achieves excellent protection performance. PTG SSD is designed with a single-pole assembly free structure, which makes it user-friendly.