How to properly install a current transformer
May 18, 2026| 1. Installation Direction and Polarity: The primary side of the current transformer has terminals P1 and P2 (or L1 and L2). Current should flow into P1 and out through P2.
During installation, terminal P1 must face the power supply side (e.g., the top of the transformer or switchgear), and terminal P2 must face the load side; otherwise, metering may be reversed or protection may malfunction.
The secondary side corresponds to S1 and S2. S1 is connected to the positive terminal of the measuring equipment, and S2 must be reliably grounded to prevent high voltage from entering the secondary circuit.
2. Primary Side Installation Requirements: For through-hole type current transformers, ensure that the conductors pass vertically through the center hole to avoid eccentricity or tilting, which could affect magnetic circuit closure.
When multiple cables pass through, ensure that the three-phase cables are symmetrically centered, especially in zero-sequence current measurement, as asymmetry can lead to errors.
After installation, open-type current transformers must have both halves aligned and securely fastened to prevent magnetic circuit leakage from affecting performance.
3. Secondary Side Wiring and Safety Specifications
Secondary circuit conductors should use 2.5mm² or larger copper core wires, and the length should not exceed 50m to reduce voltage drop.
Open circuit on the secondary side is strictly prohibited: An open circuit during operation will induce high voltage (up to several kilovolts) on the secondary side, endangering personal and equipment safety. Before replacing instruments, terminals S1-S2 must be short-circuited.
Grounding must be secure. Terminal S2 should be connected to a dedicated grounding copper busbar, not to the cabinet bolts, to avoid poor contact.
4. Environmental and Fixing Requirements
The installation location should avoid strong electromagnetic interference sources, and the vertical installation tilt should be ≤1°.
The mounting bracket should be stable to prevent loosening due to vibration; when installed inside a distribution box, a ventilation space of ≥80mm should be reserved at the top.
