CT Ratios Calculation

I dread to answer such a simple question on such a dangerous application where the qualified electrical engineer designer should know, so I am closing my eyes while I answer the question as follows.......

The ratio is chosen by looking in the relay manual to see what current inputs the relay accepts (to get the CT secondary current value) while the primary current value is chosen by calculating the maximum current running through the CT primary followed by selecting a CT that has the same or higher primary current rating. The two make up the ratio.

Get someone qualified to check your work before you submit your tender/order the CT/submit your homework, etc.

_{Jack - I am qualified to do this, are you?}

thank you for your input. I know it is somewhat a straight question to ask. what concerned me is that these line CT's are for differential scheme. and I wanted to make sure before rushing into selection.

This is obviously homework.

No company would hire someone to do this work who would then have these questions.

You are not qualified, and any company would clearly see this...as do you.

thank you for such a reply. you could have provided an educational feedback instead of such a judgmental one