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What does CT “burden” mean?

Why do you care about burden when ordering current transformers?

Many of our customers regularly request quotes for standard and custom 5A ratio type current transformers but only ask for the window size and the input current with no knowledge of the “burden”. The burden is specified as VA or resistance (or impedance). We can not guarantee the accuracy without the burden.

The burden is the termination impedance of the measuring instrument. The measuring instrument can be an analog or digital energy meter, a data logger or a recorder. All instruments that use a current transformer to measure line current must terminate the CT with a resistance (impedance in same case which means there is some inductance involved).

A CT supplier should be given the burden when ordering. Technically, the total burden for a CT is the internal winding resistance, the connecting lead resistance and the measuring instrument input resistance.
Some CTs are installed a long distance from the measuring instrument and the connecting leads can have a resistance as much as 0.002 ohms per foot (both ways because the current makes a complete round trip). This resistance will cause an error if not taken into account.

Below is a table of CT burdens that you can use to tell your CT supplier full information about what you need in addition to input current and window opening:

Burden_Resistor_Chart

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