Leakage protector installation necessity - Solutions - Huaqiang Electronic Network

Photocoupler

The protection zero is generally adopted by the TN-CS system or the TN-S system, that is, the neutral line is repeatedly grounded before the power is put into the household, and the repeated grounding resistance is ≤10 Ω. After entering the household, the working zero line N and the protective zero line PE must be separated. At this point, the wire is connected to the metal casing of all electrical equipment through the grounding hole of the three-hole socket. After the zero line is introduced into the Distribution Box, it should be insulated from the ground like the phase line. If the phase line is short-circuited, the short-circuit current forms a closed loop through the neutral line and the ground. At this time, the loop impedance is small, and the short-circuit current is large, so that the large short-circuit current causes the protection switch to trip, and the power supply circuit is cut off to achieve the purpose of safety protection. Figure 1
Shown. Short circuit current IK = U/Zd where:
IK-phase line short-circuit current, A
U - phase voltage,
Zd — the sum of the neutral impedance and the repetitive grounding resistance, Ω
However, the TN-CS system can only protect the casing of the electrical equipment from being charged when it is charged, but not the phase-to-ground short circuit.
The reason is: when the phase is short-circuited (that is, the single-phase short-circuit caused by the insulation damage of the equipment, referred to as the fault short-circuit), the short-circuit current is naturally contacted by the device and the ground, and the resistance flows to the neutral point of the power source. Since the natural contact resistance is large at this time, and the short-circuit current is small, it is not enough for the fuse and the circuit breaker to operate, and the circuit is cut off, but the arc spark caused by the fault can be sustained for a long time or even ignited. as shown in picture 2.

In order to overcome the above problems, the installation of leakage protector in building electrical design and construction has become an effective means of protection against electric shock or leakage.
In addition, the installation of leakage protectors in residential buildings is also the need for design and construction in accordance with the national standard GB6829295.