7 Simple How to Find Current Transformer (CT) Polarity

7 Simple Ways to Find CT Polarity:

Current Transformer is used to sense the primary line current. Generally current transformer is called as CT. CTs are two terminal equipment. The output current from the CT comes from one terminal and the same amount if current return to the same CT after circulating the other electrical devices.

The output from the Current Transformers are directly given to the electrical sensing devices such as protection relays, energy meter, current measurement meter etc. to get exact result from those devices, the current transformer’s terminal polarity to be connected correctly with the devices polarity.

Otherwise (polarity reversed), the devices starts malfunctioning, i.e energy meter shows negative readings, relay may read negative current hence relay may activate the trip circuit, reverse power relay activation is alternator or generator circuits etc. Let’s see how to identify the current transformer polarity…

Method 1: Identify through Ferrules numbering:

Ferrules identification is a core of our electrical circuit. Ferrules are nothing but a numbering the cable terminal with the plastic ring punched. It uses to read an electrical circuit by anyone.

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Here the CT terminals are numbered by S1 and S2. The S1 and S2 numbers are unique number for CT cable and both the number are mentioned in tail end and head end. Tail end means panel board are junction box side and head end means CT terminal side…

Method 2: Using manufacture sticker P1 and P2.

Normally CT P1 mentions the current entering side and P2 says current leaving side. By the way you can identify, the current entering terminal is S1 and Current leaving terminal as S2.

Method3: Using K and L identification:

Some of the manufactures use the K and L mark instead of P1 and P2. The same way K mentions current entering terminal S1 and L mentions the current leaving terminal S2.

Method 4: Current Entering and leaving:

The primary current entering terminal is S1 and the primary current leaving is S2.

Method 5: Using MOV terminal

The MOV means Metal Oxide Varister. It is used to protect the circuit against high voltage. In MOV use to protect the current transformer from secondary open circuit disaster. The MOV is installed CT S1 terminal by the way you can identify.

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Method 6: Connecting Energy meter

This method is field test method. You have to connect the current transformer to the energy meter. If the energy meter shows the negative value means you have to change the polarity of the connection either CT or energy meter side.

Method 7: Using Modern Testing equipment:

Some of the modern testers are used to identify the CT polarity in offline.

Video Tutorial for Identifying CT Polarity:




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