How to ground a current transformer?

I. Grounding Principles and Location
1. Single-Point Grounding:
On the secondary side, grounding is permitted only at the S2 terminal. Multiple grounding is prohibited (to prevent circulating current interference).
The grounding wire must be connected directly to the dedicated grounding busbar on the power distribution cabinet; it must not be connected to non-standard locations such as the cabinet door.
2. Metal Casing Grounding:
The transformer's metal casing must be grounded independently, separate from the secondary circuit grounding point, to prevent interference.
II. Wiring Procedures
1. Secondary Grounding:
Reliably ground the S2 terminal using a copper wire (cross-section ≥ 2.5 mm²) to ensure a ground resistance of ≤ 4Ω.
In a three-phase system, the S2 terminals of all transformers must be short-circuited and then grounded together.
2. Isolation of the Primary and Secondary Sides:
The primary side (P1/P2) and the secondary side (S1/S2) must be strictly separated to avoid reverse polarity (L1/K1 are the same terminals). III. Safety Precautions
1. Opening the secondary side is strictly prohibited:
During operation, an open secondary side circuit can generate high voltage (up to several thousand volts), potentially damaging equipment or endangering personnel.
Grounding provides a discharge path, reducing risk.
2. Insulation Inspection:
Before installation, ensure that the transformer insulation is intact and the grounding wire is not loose or corroded.
IV. Special Scenarios
Zero-sequence current transformer: The cable ground wire must pass through the transformer's center hole to ensure that the ground current is detected.
Low-voltage system: If the secondary side voltage is low, grounding may be omitted after evaluation, but the insulation level must be ensured to meet the standard.