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What is the recommended wire size for extending the current transformer (CT) wire length?

Issue:

What is the recommended wire size for extending the current transformer (CT) wire length?

Product Line:

Current Transformer

Environment:

Current Transformer

Cause:

Customer is requesting to extend the length of the CT with minimal accuracy discrepancy.

Resolution: 

Typically 12 Gauge is used for lengths between 0 to 25 feet, 10 Gauge for 25 to 50 feet, and 8 Gauge for over 50 feet.
Extending the cable adds resistance (burden) to the current circuit, so the idea is to minimize the amount of resistance in the wiring so that the accuracy is affected at a minimum.

Follow the steps and chart below for a more accurate selection in wire gauge.

  1. From CT specification/data sheet, find the rated secondary current (typically 5A) and burden at rated accuracy
  2. On the top chart, use a straight edge to draw a line from the first column through the second column, to the third column.  Use the values in step one for the intersection points for the first and second column.
  3. Read the Impedance from the third column.  This will be used for the bottom chart to determine the wire size.
  4. On the bottom chart, use a straight edge to draw a line from the impedance value determined in step 3 to the approximate distance from the CT to the input of the meter, including the connection to the CT shorting block.  Extend this line to the first column to determine the wire size.
  5. If the extended line falls between two wire sizes, use the larger wire size (note: smaller AWG # is larger wire size)
 



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