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Low voltage switchgear and controlgear

Basic concepts:
Switchgear and control equipment is a basic term, which includes switchgear and its combination with auxiliary control, detection, protection and adjustment devices. It also includes the combination of electrical appliances and devices with internal wiring, auxiliary devices, housing and supporting structural parts. Switchgear is used for power generation, transmission, distribution and electric energy conversion functions. The control equipment is used for the control function of the power consumption device.

Switchgear and control equipment involve three basic concepts:

• isolation
For safety, cut off the power supply or separate the device or bus section from each power supply to form an isolated section of the device (for example, when it is necessary to work on a live conductor). Such as load switch, disconnector, circuit breaker with isolation function, etc.

• control (on-off)
For the purpose of operation and maintenance, connect or disconnect under normal operating conditions. Such as contactor and motor starter, switch, emergency switch, etc.

• protection
To prevent abnormal conditions of cables, equipment and personnel, such as overload, short circuit and grounding fault, the method of disconnecting fault current is used to isolate the fault. Such as: circuit breaker, switch fuse group, protective relay and control appliance combination, etc.


1. Fuse:
It is mainly used as short-circuit protection. When the circuit is short circuited or seriously overloaded, it will automatically fuse and cut off the circuit for protection. It is divided into general type and semiconductor special type.

2. Load switch / fuse switch (switch fuse group):
Mechanical switching devices that can connect, carry and disconnect normal current and carry current under abnormal conditions (these switches cannot disconnect abnormal short-circuit current)

3. Frame circuit breaker (ACB):
The rated current is 6300A; Rated voltage to 1000V; Breaking capacity up to 150ka; Protection release with microprocessor technology.

4. Molded case circuit breaker (MCCB):
The rated current is 3200A; Rated voltage to 690V; Breaking capacity up to 200kA; The protection release adopts thermal electromagnetic or microprocessor technology.

5. Miniature circuit breaker (MCB)
The rated current is not more than 125A; Rated voltage to 690V; Breaking capacity up to 50kA

6. Thermal electromagnetic protection release is adopted
Residual current (leakage) circuit breaker (rccb/rcbo) RCBO is generally composed of MCB and residual current accessories. Only the miniature circuit breaker with residual current protection is called RCCB, and the residual current protection device is called RCD.

Post time: Jul-04-2022