1, 3P is used for three fire wire wiring, that is, 380V wiring, generally used for 380V electrical appliances. 4P is used for three fire and one zero wiring, usually used for 380V electrical appliances with a zero line, and of course, can also be done as a master switch. 3P is a three-open, three-phase control, three inbound (outbound) terminals, into the three fire wires. Usually used for three-phase power bus switch and three-phase electrical equipment. 4P is in the three open on the basis of adding a terminal, for the zero terminal with N said.
2, 1P, 2P is used for single-phase; 3P, 4P is used for three-phase. When used for protective zero, only 1P, 3P; and when used for protective grounding, it is best to use 2P, 4P. And 1P + N only in the phase line with a protector, when the work at the same time disconnect the phase line.
The 3, 4P switch's have two uses.
One, for electrical isolation, used to disconnect the neutral line, to ensure the safety of maintenance personnel during electrical maintenance, our country in the past, widely used in the so-called zero protection of the TN-C system, because of the system's neutral line is the PEN line, can not be cut off with a gate knife, the line is commonly used in the 3P switch, in the process of electrical maintenance, the N line is not completely isolated resulting in a click of the accident. And 4P switch can effectively disconnect the N line, play the role of electrical isolation.
Two, used as a functional switch, such as dual power automatic switching device (ATS). However, 4P switch use process there is a risk of breaking "zero", so in the power supply and distribution design should be careful to use 4P switch.
Expanded information:
Operating Principle of Air Switch
There are 3 types of stripping methods: thermoactive, electromagnetic and compound stripping. When a general overload occurs in the line, the overload current can not make the electromagnetic release action,
but can make the thermal element to produce a certain amount of heat, prompting the bimetal heat upward bending, push the lever to make the hook and latch disconnect, the main contact break, cut off the power supply. When a short circuit or serious overload current occurs in the line, the short circuit current exceeds the value of the instantaneous debugging current, the electromagnetic debugger generates a large enough suction force to suck the armature and hit the lever, so that the hitch rotates upward around the rotating axle seat to disengage from the locking device, which breaks the three main contacts and cuts off the power supply under the action of the spring counterforce.
The disconnecting mechanism of the switch is a set of connecting rod device. When the main contacts are closed by the operating mechanism, they are locked in the closed position by the locking hook. If a fault occurs in the circuit, the relevant striker will act to disengage the locking hook in the striker mechanism, so the main contact is quickly broken under the action of the release spring. According to the different protective role, the release can be divided into overcurrent release and loss of voltage release and other types.