How to avoid incorrect installation of current transformers
Jun 05, 2026| 1. Prevent Reversed Polarity and Direction
P1 must face the power supply side (e.g., transformer or incoming line), and P2 must face the load side.
On the secondary side, S1 is connected to the instrument's positive terminal, and S2 is connected to the negative terminal and grounded.
After installation, use a DC method or a polarity ratio tester to verify the polarity on-site, ensuring that P1 and S1 are the same terminal.
2. Prevent Open Circuits on the Secondary Side (Most Crucial Safety Measure)
Fuses or switches are strictly prohibited from being installed in the secondary circuit to prevent open circuits caused by misoperation.
Before repairing or replacing instruments, the S1-S2 terminals must be reliably shorted with a jumper or shorting wire before proceeding.
After wiring, check that all terminals are secure to prevent loosening and open circuits during operation.
3. Proper Grounding, Prevent Multiple Grounding Points
The S2 terminal must be reliably grounded at one point, connected to the dedicated grounding copper busbar in the control room. Do not connect it to the cabinet or bolts to avoid poor contact.
Simultaneous grounding at both ends S1 and S2 is strictly prohibited, as this will create a circulating current and cause the protection device to malfunction.
4. Ensure Primary Side Installation Quality: For through-hole type CTs, the conductors should pass vertically and centered through the central hole to avoid eccentricity or tilting affecting magnetic circuit closure.
When multiple cables are through-hole, the three phases should be arranged symmetrically, especially in zero-sequence current measurement, as asymmetry will lead to errors.
Open-type CTs must be completely closed and the screws tightened after installation to prevent magnetic circuit leakage from affecting performance.
5. Reasonable Selection of Turns Ratio and Matching Load: The turns ratio should ensure that the normal operating current is within 60%~120% of the rated value to guarantee measurement accuracy.
The total impedance of the instruments connected to the secondary side must not exceed the CT's rated capacity (e.g., 15VA), otherwise it will cause increased errors or core saturation.
6. Environmental and Fixing Requirements: The installation location should be dry, well-ventilated, and away from strong electromagnetic interference sources.
Vertical installation tilt ≤ 1°, and the bracket should be firmly fixed to prevent vibration and loosening. When installing inside the distribution box, leave ≥ 80mm of ventilation space at the top to avoid overheating and affecting its lifespan.
