Polarity Testing of an Unmarked CT

Normally the hole or the big terminals is the primary side. The small terminals are the secondary side.

If your ct has a big hole through the centre, put a conductor (copper wire) through the hole. Connect a direct current Avo meter (with a centre zero scale on the mili volt setting) on the secondary of the CT.

Use a car battery (12v) and connect the negative to the one side of the piece of conductor. Flick (connect quickly and release) the positive side of the battery on the other side of the conductor. While doing this look at the avo meter.

If you get a reading to the positive side of the meter, it means that the secondary terminal connected to the positive side of the avometer is the same as the primary positive. In other words this will be P1 and S1 of the CT.

Normally the hole or the big terminals is the primary side. The small terminals are the secondary side.

What can I say, that's about as good a layman's answer as you are going to get.

f you are also trying to figure out the turns ratio of the secondary then you will need to pass a known current thru the primary. If you don't fully understand what I have just said above STOP as an open-circuited secondary side of a CT can kill. Learn more about current transformers before proceeding any further.

http://en.wikipedia.org/wiki/Current_transformer

Can you provide more information on what type of CT you have and your application?