How to Mount a Current Transformer (CT) in a Compressor

How to Mount a Current Transformer (CT) in a Compressor

A current transformer (CT) helps measure the electrical load on your compressor’s motor. Correct placement, wiring, and safety procedures ensure accurate readings and trouble-free operation.
A CT measures motor current indirectly by detecting the magnetic field around a conductor.
It’s commonly used for:
  1. Motor load monitoring
  2. VFD (Variable Frequency Drive) feedback
  3. Motor protection and diagnostics

How to install a CT

Alert
Safety First! Before you start:
  1. Isolate power – Perform lockout/tagout on the compressor.
  2. Verify with a multimeter that no voltage is present.
  3. Wear PPE – Gloves and safety glasses are recommended.

Choose the Right CT
Select a CT that:
  1. Matches or slightly exceeds the motor’s maximum current rating (e.g., a 100 A CT for motors up to 100 A)
  2. Has the correct output type for your controller or meter (5 A, 1 A, or 0.333 V)
  3. Fits around the motor cable’s size
For clarification of which CT you must use, we refer to our Support Article where you can find a detailed Table.

Identify the Correct Cable
Locate the motor supply cable after the contactor or VFD output.
Only pass one phase conductor through each CT and do not pass multiple conductors through a single CT unless it’s a 3-phase CT — doing so will cancel out the measurement.

Install the CT
  1. Open, place around the selected phase conductor, and latch securely.
  2. Follow orientation markings (arrows should point towards the motor).
  3. Secure with cable ties to prevent movement.



Connect the CT to DRIVE+
  1. Use twisted-pair shielded cable for wiring between the CT and DRIVE+
  2. Keep the wiring short and away from high-voltage cables. This to prevent that we have any interference with the signal due to the High-Voltage cables.

Never install on live wiring — even split-core CTs require a power-off panel.
For VFD-driven compressors, mount the CT on the output side (between VFD and motor).
Label the CT’s location for easier future servicing. This makes it easier to identify the use of the installed CT if it is required.

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