Why must you short out the secondary terminals on a current transformer when removing the ammeter from circuit

Answer 1

Your open circuit current transformer is effectively a voltage transformer with a very small number of primary turns (often just one) and a large number of secondary turns.

For example a 500/5 CT (turns ratio of 100) on a 480v circuit could produce 480 X 100 = 4,800v (not quite this high in practice)

This high voltage created will break down the insulation of the CT windings and burn it up. There are stories of extreme cases where the CT has exploded, I don't know if they are true. Also the high voltages produced on this control wiring could be hazardous.

Answer 2

You must never open circuit a CT as an explosively large voltage will be induced across the terminals.

Answer 3

Current through the primary will induce high voltage between the secondary leads of the CT. Not only is this a hazard to human life, it can and will cause insulation failure and/or equipment damage.

Answer 4

To prevent potentially lethal voltages from appearing across them.

Several people around here don't seem to understand what a 'current transformer' even is. Suggest you study a bit and find out ☺

Doug

Answer 5

Just to break the stalemate, Doug has it right.

Edit, The earlier wrong answer has been removed, making my comment meaningless, but there WAS a wrong answer, and Doug's is still right.

Answer 6

Go Dougie!