A miniature circuit breaker(mcb) is a small-capacity plastic case circuit breaker with a very compact structure. It is generally composed of an operating mechanism, contacts, protection devices (various trip units), and an arc extinguishing system. Miniature circuit breaker is a kind of complex electrical apparatus. In addition to the correct selection and adjustment, it must be properly maintained to ensure its safe operation.

Miniature circuit breakers

Notes on installation of miniature circuit breaker

After the circuit is connected, check whether the wiring is correct. If the miniature circuit breaker can breaking normally, it indicates that the leakage protector is installed correctly. Otherwise, check the circuit and eliminate the fault. After the leakage protector is put into operation, the user should check whether the miniature circuit breaker operates normally through the test button after a period of time. (the function of the test button is to check the operation state of the miniature circuit breaker when it is closed and energized after it is newly installed or operated for a certain period of time). Press the test button, the miniature circuit breaker can break off, indicating that it operates normally and can be used continuously. If the miniature circuit breaker can not be disconnected, it means that the miniature circuit breaker or circuit has fault, and it needs to be checked.

Four pole leakage miniature circuit breaker must be connected to the zero line to make the electronic circuit work normally.

The load wiring of the small leakage circuit breaker must pass through the load end of the miniature circuit breaker. It is not allowed that any phase line or zero line of the load does not pass through the small leakage circuit breaker. Otherwise, the artificial "leakage" will cause the miniature circuit breaker to fail to close and cause "misoperation". In addition, in order to protect lines and equipment more effectively, leakage miniature circuit breaker and fuse can be used together.

In order to reduce the occurrence of "zero breaking" accident of three-phase circuit, it is necessary to avoid installing unnecessary miniature circuit breaker contacts on the neutral line, that is, under the condition of ensuring the safety of electrical maintenance, four pole miniature circuit breakers should be installed as little as possible.

No matter whether there is total equipotential bonding in the building, the miniature circuit breaker of TT system power incoming line should realize the isolation of neutral line and phase line at the same time, but the TN-S system and TN-C-S system with total equipotential connection do not need this kind of building electrical equipment.

Except for the miniature circuit breaker with leakage protection function, other power conversion miniature circuit breakers do not need to isolate the neutral line.

No matter what kind of grounding system, the small circuit breaker of single-phase power supply incoming line shall be able to disconnect phase line and neutral line at the same time.

For different types of miniature circuit breakers, different instantaneous release and corresponding current grade products are selected. When selecting the rated current and the corresponding instantaneous release, the rated current of the load and the maximum short-circuit current that may be output must be considered. When the maximum short-circuit current is greater than or equal to the setting value of B, C, D type instantaneous release, the short-circuit protection can work.

Before installing leakage protector, the original power supply protection type of miniature circuit breaker must be made clear so as to judge whether it can be directly installed or need to be modified. Before the installation of leakage miniature circuit breaker, some equipment have adopted some power supply protection types, but some protection types are not suitable for direct installation of leakage miniature circuit breaker, otherwise it will cause misoperation or refuse to operate the switch.

Before installing the miniature circuit breaker, it is necessary to carefully check the position of the incoming and outgoing line ends of the installed miniature circuit breaker. It is not allowed to connect in reverse. During the installation, it is necessary to pay attention to the safety of electricity consumption. It is better to install the circuit breaker in a special distribution box and operate it by the personnel with electrician's license.

Matters needing attention in maintenance and use of miniature circuit breaker

Before use, wipe the rust proof grease on the working face of electromagnet to avoid affecting its action value.

During regular maintenance, the dust falling on the automatic switch shall be removed to avoid reducing its insulation.

After using for a certain number of times, the burr and particles on the contact surface should be removed; when the contact wear exceeds 1 / 3 of the original thickness, it should be replaced.

Once the setting value of the release is adjusted, it should not be changed at will, but it should be checked regularly to avoid misoperation or non action of the release. After long-term use, check whether the spring is rusty and stuck, so as not to affect its action. For semiconductor release, its action should be checked regularly with test button.

After breaking the short-circuit current of the miniature circuit breaker, the contact should be checked in time when the superior power supply is cut off. If serious electric burn marks are found, dry cloth can be used to wipe off; if the contact points are found to be singed, fine sandpaper or fine grain file can be used for careful trimming. However, the main contact is generally not allowed to be trimmed with a file.

The dust on the circuit breaker should be removed regularly and the action value of various releases should be checked. The operating mechanism usually fills the transmission part with lubricating oil every two years.

After breaking short-circuit current or using for a long time, the metal particles and black soot on the wall and grid of the interrupter should be removed to maintain good insulation and arc extinguishing performance.

It is not allowed to take down the arc extinguishing cover during operation, and it should be replaced in time when it is damaged, so as to avoid the accident that the current cannot be extinguished in case of short circuit.

If the miniature circuit breaker is disconnected due to the fault of the protected circuit (leakage, overload or short circuit), the operating handle should be in the tripping position (middle position). After finding out the cause and eliminating the fault, pull down the operating handle (i.e. put it in the "off" position) to make the operating mechanism "buckle again" before closing operation (please note the different meanings of three positions of the operating handle of miniature circuit breaker).