Grounding Current Transformers


Thread Starter


Why does a Current tranformer have a ground terminal on secondary side?
What purpose does this serve? The reason i want to know this is that, i observe a different behavior in secondary voltage when the secondary is grounded.

Can anyone help me with this?


Curt Wuollet

It serves several purposes, one being safety in case of an insulation breakdown. Since the secondary is isolated and there should be no potential to ground, grounding it shouldn't produce any change in a _valid_ reading with an indicator that can be referenced to ground. If it does, you have noise or leakage or something that changes with the ground. Unless whatever you are reading it with is referenced to something else or not isolated, I would tend to believe a referenced reading before a floating one.


Q1: The ground-terminal protects endangerment of human life if there is a primary-insulation failure resulting in energization of the secondary winding at primary-voltage level.

Q2: "...I observe a different behavior..." This is indicative of either a faulty CT, or a an external wiring error.

Phil Corso