How to properly install a residual current transformer?
Sep 19, 2025| 1. Pre-installation Preparation
Power-off Operation: Ensure the circuit is completely de-energized. Wear insulating gloves and safety glasses. Check that the transformer is intact and of the correct specifications.
Tools and Materials: Use copper wire with a cross-section of 2.5 mm² or greater for the secondary circuit. Number the wire ends to avoid confusion.
2. Installation Steps
Securing Position:
Drill holes in the panel and secure the transformer base with screws to ensure a secure fit.
The installation location should be near the starting or ending point of the circuit, away from strong magnetic objects (such as iron).
Wiring Requirements:
Three-phase, four-wire system: The three-phase live wires (A, B, and C) and the neutral wire (N) of the circuit breaker output must all pass through the transformer hole. The protective ground wire (PE) must not pass through.
Single-phase system: Both the live and neutral wires must pass through the transformer. 3. Wiring Specifications
Polarity Check:
The primary (P1/P2) and secondary (S1/S2) terminals must be wired according to the reverse polarity principle to avoid reverse polarity, which can cause measurement errors or false protection trips.
On the secondary side, connect S1 to the positive terminal of the instrument, S2 to the negative terminal and ground, and unused windings must be short-circuited and grounded.
Grounding Requirements: The secondary output must be grounded at a single point to prevent interference.
4. Testing and Verification
Power-on Test: Apply power gradually from the low-voltage side and use a multimeter to check whether the output current is normal.
Function Verification: Simulate a leakage current (such as grounding the neutral line) to confirm whether the protective device trips within 30mA (for household use) or the set threshold.
Common Errors and Precautions
Do not open the secondary side: This may result in dangerous high voltage.
Avoid multiple grounding points on the neutral line: This will disrupt current balance and cause false trips.
Regular Maintenance: Clean the housing and test response speed and functionality.
