22

I have an oportunity today to fit my additional ct coils purchased from the shop to my bare busbar today. I have yet to reprogram my new emontx to which they will be connected to a 3 phase sketch or install it physically in position. I will power down to install them however would it be safe to leave them unplugged when the power is back on, or should I short cuircit them?

23

This page in Learn says:

If an unburdened CT (i.e. one without a burden resistor) is attached to a current-carrying conductor, the CT will generate an unsafe voltage at its leads which could break down the insulation and destroy the C.T.

The YHDC transformer sold in the Shop has internal Zener diodes to limit the maximum unburdened voltage output to a safe level. CTs with internal burden resistors (‘the voltage output’ type) are also protected against developing dangerous voltages.

Always connect the C.T. leads before clipping it round a current-carrying conductor, and always un-clip the C.T. from the current-carrying conductor before disconnecting its leads.

Never open-circuit a C.T. whilst it is on a current-carrying conductor. It is always safe to short-circuit a C.T.

24

And never trust the built-in protective device to make the CT “safe.” (Zener, TVS, etc.)
i.e. never assune an open-circuited CT on a live current-carrying conductor is safe just because it has diodes, etc, built in.

25

A c.t. when short-circuited has the minimum load - normal current, zero voltage. If you invert everything you know about a ‘normal’ voltage transformer, you won’t be too far wrong for a current transformer.

26

Hi thanks everybody for your replies. Ill short circuit them before putting the load back on.