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Simple Guide to Installing a Three-Phase kWh Sub Meter and CTs

Tools and Materials Needed

  •  Three-phase kWh sub-meter (compatible with your voltage and current requirements).
  • Current Transformers (CTs) rated for your system.
  • Electrical panel and necessary breakers.
  • Screwdrivers and pliers.
  • Wire stripper and cutter.
  • Voltage-rated wiring.
  • Insulation tape and cable ties.
  • Personal Protective Equipment (PPE) (gloves, goggles, etc.).
  •  Multimeter for verification.
  • Installation manual for your specific sub-meter model.

Steps for Installation

Preparation

  • Turn off the main power supply to the panel where the sub-meter will be installed.
  • Ensure you are familiar with the electrical schematic and wiring diagrams for your sub-meter and CTs.
  • Confirm that your sub-meter and CTs are rated for the correct voltage and current for your system.

Mount the kWh Sub-Meter

  • Locate a suitable spot on or near the electrical panel.
  • Secure the sub-meter with screws or DIN rail mounts, as required.

Install the Current Transformers (CTs)

  • Identify the three-phase conductors (L1, L2, L3) in your panel.
  • Place each CT around the corresponding conductor. Ensure the orientation follows the marked arrow (often labelled "Load" or "P1") to point toward the load.
  • Tighten the CT around the conductor securely.

    Wire the CTs to the Sub-Meter

  • Connect the secondary wires from each CT to the corresponding input terminals on the sub-meter (e.g., CT1 to L1, CT2 to L2, CT3 to L3).
  • Use the colour codes or labels provided in the installation manual for correct polarity (S1 and S2 terminals).

    Connect the Voltage Inputs

  • Connect the phase wires (L1, L2, L3) and neutral wire to the voltage input terminals on the sub-meter.
  • Use appropriate fuses or breakers for protection as recommended in the sub-meter manual.


    Verify Connections

  • Double-check all connections:
  • Correct CT to phase matching (CT1 to L1, CT2 to L2, CT3 to L3).
  • Voltage connections are properly aligned to the respective input terminals.


    Power Up and Test

  • Turn the power back on.
  • Use a multimeter to verify that the voltage inputs to the sub-meter are correct.
  • Check that the sub-meter powers on and displays correctly.
  • If your sub-meter requires programming for CT ratios or system configuration, follow the manual to input these settings.


    Secure Wiring

  • Bundle and secure loose wires with cable ties.
  • Ensure all connections are insulated and safe from accidental contact.


    Verify Functionality

  • Confirm that the sub-meter is correctly measuring the voltage, current, and energy usage for all three phases.
  • Compare readings with a known load or reference meter to ensure accuracy.


    Tips for Safe Installation

  • If you are not experienced with electrical systems, hire a licensed electrician to perform the installation.
  • Adhere to local electrical codes and regulations.