Types and principles of leakage action of leakage circuit breakers - News - Global IC Trade Starts Here.

In the TN-CS system, if the detection circuit is placed between the PEN conductor and the live (L) line in the TN-C section, a leakage current on the PE line of the TN-S section may cause the residual current device (RCD) to fail to operate. This happens because the RCD is not detecting the leakage current correctly due to the configuration of the system. In a TN-S system, if the neutral (N) line is mistakenly connected to the switch, a break in the N line combined with a leakage on the live (L) line can lead to the RCD failing to trip. This is because the detection circuit does not sense the leakage current properly when the N line is disconnected. In a TN-CS system, if the installer incorrectly connects the N line and the PE line together, it can cause the RCD to malfunction during a leakage event. The connection between the neutral and protective earth creates an unintended path for current, leading to false tripping or failure to trip. Additionally, if the sensitivity of the RCD is set too low during installation, it may not detect small but dangerous leakage currents. This can result in the device refusing to operate even when there is a real fault present. The main causes of RCD malfunctions include: 1. Incorrect wiring where the PE and N lines are swapped in a TN-CS system, which leads to improper operation. 2. Using a three-pole RCD in a three-phase four-wire lighting and power system, causing the zero line to carry current and trigger false trips. 3. High-power electrical appliances near the RCD can generate electromagnetic interference when turned on or off, which may cause the device to malfunction. 4. Low insulation resistance between phase and neutral lines can allow some current to leak to ground, creating unbalanced currents that confuse the RCD’s zero-sequence transformer. 5. Connecting the PE line of equipment casing to the working neutral line can create a path for leakage current, triggering unwanted trips. 6. If the three-phase power lines are not passed through the zero-sequence transformer in the same direction, it can cause incorrect current balance and lead to malfunctions. 7. Setting the RCD sensitivity too high can result in unnecessary tripping, even under normal operating conditions. These issues highlight the importance of proper installation, correct selection of devices, and regular maintenance to ensure the reliable performance of residual current devices. Understanding these common problems can help electricians avoid mistakes and improve the safety and efficiency of electrical systems.

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