Must the low voltage disconnector lag behind the low voltage circuit breaker?

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Must the low voltage disconnector lag behind the low voltage circuit breaker?
07 20 , 2021

Is there such a view that the disconnector is a low-level, and the circuit breaker is a high-level, where the disconnector is used, the circuit breaker can be used instead? This idea is debatable, but disconnectors and circuit breakers have their own applications.

Low voltage circuit breaker is a mechanical switching apparatus that can make, carry, and break current under normal circuit conditions, and can also make, carry, and break fault current for a certain time under abnormal conditions such as short circuit. Low voltage circuit breakers can be divided into frame circuit breakers (ACB), molded case circuit breakers (MCCB) and micro circuit breakers (MCB). The low voltage isolator switch has the function of isolator and switch. First of all, it has the isolation function. At the same time, it can be connected, withstand and break the load current under normal circumstances. That is to say, the isolator switch has the function of both isolator and switch.

The function of the isolator is to disconnect the power supply of the electrical line or electrical equipment. At the same time, you can see the obvious disconnect point. The isolator can not protect the line or equipment. But the switch does not necessarily have isolation function, it has the function of switching on and off the load current, can withstand a certain period of short circuit current. For example, the semiconductor switch can not be used as an isolator, because the semiconductor switch electrical appliances are not physically isolated, exceeding the requirements of the leakage current of the isolator is less than 0.5mA, so the semiconductor must not be used as an isolator.

In fact, there are many applications of the isolator switch, but in some places, the use of the isolator switch is replaced by the circuit breaker, especially in the civil field, which not only fails to design and construction in accordance with the requirements of the specification, but also increases the cost of the project. The applications of the disconnecting switch are as follows:

(1) The upper main distribution cabinet is protected by circuit breakers or fuses, and the radiation-type power supply mode is adopted to enter the household. There is no branch in the middle of the power supply line. The cable inlet switch to the distribution cabinet should be isolated.

(2) Separating appliances should be set on the main circuit of the two power inlet lines of the double electric source cutting device, and special isolating switches should be used.

(3) whether the low voltage power distribution cabinet needs to be installed separately needs specific analysis, if the low voltage power distribution cabinet is a cabinet of drawers, you can not set up the isolation appliance, because the cabinet of drawers can be the circuit breaker and other overall out; If the low voltage distribution cabinet is a fixed cabinet, a disconnecting switch must be installed or a circuit breaker with an isolating function must be used.

(4) The total incoming line of the cable branch box should adopt a special disconnecting switch, and each branch circuit should adopt a fuse type disconnecting switch or MCCB with complete isolation function.

In short, in order to facilitate the maintenance, testing and overhaul of electrical lines or electrical equipment, it is essential to install a disconnecting switch in a place that is easy to operate and easy to observe.

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