The residual current transformer should distinguish the phase line, N line and PE line in the power grid before threading. The phase line and the N line must pass through the residual current transformer together, and the PE line cannot pass through the transformer.
In the system, if the N line does not pass through the transformer together with the phase line, once the three-phase load is unbalanced, there will be current flowing through the N line, and the detector detects a current signal, and a malfunction occurs. If the PE wire passes through the transformer together with the N wire and the phase wire, it will cause refusal or malfunction of the monitoring detector. The N lines between different circuits are not connected at many points or are repeatedly grounded, otherwise it will cause malfunctions. During the trial operation of the system, the leakage current value is too large and an alarm occurs, a large part of which is caused by this situation.
Not all residual current monitoring needs to pass the phase wire into the transformer, the total residual current monitoring method of the TN-S system can be excluded, it can only wear a cable to pass the residual current transformer. The advantage is that a small residual current transformer can be used to improve the measurement accuracy; later, if the transformer fails, it is easy to maintain.
There is no problem with the direction of installation of the residual current transformer. The transformer can be hung directly on the cable or fixed in the distribution box. It should be installed in a place convenient for maintenance, as far as possible away from strong magnetic fields.
The installation of the residual current transformer and the upper or lower end of the switch breaker will not affect the monitoring of the protected circuit. In order to facilitate later maintenance, it is better to install it at the lower port of the switch. It is not necessary to power off the upper-level switch during power-off and overhaul, just disconnect this level switch.