Installing a CT in a switchgear cabinet requires careful planning, precise mechanical work, and strict adherence to safety and clearance requirements. The confined space and proximity to live conductors make this a particularly demanding installation environment.
The first step is to verify that the switchgear has been de-energized and locked out. De-energize the primary conductor whenever possible before installing, removing, or repositioning the CT. Use lockout/tagout, arc-flash PPE, and site-approved live-work procedures where applicable. Inspect the CT for any damage before installation, and verify that its ratings are suitable for the application.
Mechanical mounting is the next critical phase. The CT must be mounted horizontally and vertically level, with the base fitted flush against the cabinet mounting surface without looseness or tilt, to avoid vibration-induced noise and data fluctuations during operation-. For through-core CTs, the busbar must pass through the center of the CT window-not touching one side-to prevent magnetic field offset that would cause accuracy errors. When multiple CTs are installed side by side, maintain adequate spacing to avoid interference.
For installations on medium-voltage insulated busbars inside switchgear panels, mechanical mounting practices must ensure secure positioning while maintaining required clearance distances-. The CT should be fixed with appropriate mounting brackets or DIN rail mounting, depending on the CT model and cabinet design. Do not force the CT into position or modify the CT housing, core mating surfaces, lead wires, mounting hardware, or insulation system in any way.
Wiring and secondary connections must be completed with the same care as the mechanical installation. The secondary current wire should be routed away from high-voltage conductors and power cables. Do not run signal wires in the same conduit or bundle that carries power mains or high-level voltage or currents. Use the shortest usable length of a suitably sized cable for secondary connections, and select the cable diameter in accordance with the required length so as not to overburden the CT.
For meter and relay connections, conduit should run from the CT enclosure to the test switch portion of the meter base or socket. Metering circuit conduit must not contain LB joints, condulets, junction boxes, or flexible connections that could compromise the integrity of the circuit-.
Before energizing the switchgear, verify that the CT secondary circuit is properly connected or shorted. An open secondary can develop hazardous voltage and may damage equipment or create a shock hazard. Verify polarity and phase alignment, and ensure that the secondary circuit is grounded at one point. After energization, check the current readings on the meter or relay to confirm correct operation.