NGR CT Ratio Question

[MEP_PM]

I was told today that the CT ratio of the NGR has an affect on the system and if a 100:5 CT was used in lieu of a 50:5 CT there could be problems. If the trip device is rated for and can be adjusted to accommodate either CT ratio, I?m unclear why there could be a problem? Can anyone help me understand how the CT selection can change to system operation or cause a negative affect? The only thing I can come up with is the sensitivity of the sensor. Any thoughts?

Thanks

 

[jim dungar]

Effectively, there is a low level cut off point for the accuracy of a CT.
A 100:5 CT will not 'transform' a 5A signal in the same manner as a 50:5 unit will.

 

[SG-1]

Agree with Jim.

The higher ratio CT will introduce more error into the relay's response. You want to size the CT fairly close to the expected current.