If you are metering electricity with any of our Omnimeter models you will need to pair the Omnimeter with 1–3 Current Transformers (CTs), depending on the electrical system that you are metering. When choosing the CT model that will be best for your system, consider these factors:

  • What is the outside diameter of your wire in millimeters?  Order a CT that will fit around the wire (this is the most common ordering mistake). It is ok to oversize the CT (the wire passing through can be much smaller then the CT aperture) but if it is too small then you will need to replace the CT(s).
  • What is the amperage of your electrical system? Each CT has an amperage rating. Make sure that the CT model that you choose has an amperage rating the meets or exceeds the amperage rating of your electrical system.
  • Do you want to use solid-core CTs or split-core CTs?  Solid-core CTs are are lower priced but require you to disconnect the primary wire, slip the CT over the wire, and then re-connect the primary wire.  Split-core CTs simply clamp around the primary wire in place.

The quantity of CTs that you will need, by electrical system:

  • Use 1 CT for single phase 2-wire systems (one hot and one neutral, with or without ground)

  • Use 1 CT for 2-wire systems (two hot wires and no neutral)

  • Use 2 CTs for a 120/240V three-wire system (two hots and a neutral, with or without ground)

  • Use 2 CTs for 3-phase 3-wire systems (without neutral)

  • Use 3 CTs for 3-phase 4-wire systems (with neutral)