How to Properly Install Split Core Current Transformers?
Dec 26, 2025| I. Pre-Installation Preparation
1. Selection and Verification
Select the transformer ratio based on the load current. For example, if the measured maximum current is 820A, select an 800/5A transformer. Ensure the operating current is between 60% and 120% of the rated value.
Inspect the appearance. Use a 5x magnifying glass to check for cracks or pores in the porcelain bushing. Then, use a 2500V megohmmeter to measure the insulation resistance. The insulation resistance between the primary and secondary windings and ground should be >1000MΩ.
2. Tools and Materials
Prepare specialized tools such as a high-precision phase meter (for polarity measurement), hydraulic crimping pliers (for wire crimping), and an infrared thermal imager (for temperature rise measurement).
Use TRJ-2.5mm² soft copper wire for the secondary windings, and ≥4mm² yellow-green bicolor wire for the grounding wire. The sealing sealant should be temperature resistant from -40℃ to 200℃ and flame-retardant (V-0 grade).
II. Installation Steps
1. Power Off Operation
Ensure the circuit is powered off before installation to prevent electric shock.
2. Current Transformer Installation
Open the current transformer and clip it onto the cable being measured, ensuring the current direction aligns with the arrow on the casing.
Secure the current transformer with nylon cable ties to prevent slippage.
3. Secondary Wiring
The secondary side of the current transformer has two wires, red and black. Connect the red wire to the instrument's IA*, IB*, and IC* terminals, and the black wire to the instrument's IA, IB, and IC terminals.
The wiring must be secure to prevent loosening or oxidation.
4. Power-On Check
After verifying the wiring is correct, connect the power supply. The current transformer will begin measuring the circuit current.
III. Precautions
1. Current Direction
The current transformer cable should pass through the center point: P1 in, P2 out.
2. Current Transformer Fixing
Secure the current transformer with nylon cable ties to prevent slippage.
3. Current Transformer Wiring
When used with a multi-function meter or ammeter, connect the red wire to the meter's IA*, IB*, and IC* terminals on the secondary side, and connect the black wire to the meter's IA, IB, and IC terminals.
4. Safety Specifications
The secondary side of the current transformer must be reliably grounded at one point to prevent high voltage from entering the secondary side.
Fuses are not allowed in the secondary circuit to avoid open circuits caused by fuse failure.
IV. Common Problems and Solutions
1. Secondary Side Open Circuit: Immediately short-circuit the secondary terminals (S1-S2) and check if the wiring is secure.
2. Incorrect Polarity: Verify the polarity using a phase meter or DC method to ensure correct wiring.
3. Poor Insulation: Measure the insulation resistance with a 2500V megohmmeter. If it is <1000MΩ, replace the current transformer.
