This is very simple.Kwhr meters are available for 1 Amp or 5 Amps.therefore CT Secondary should be either 1 or 5.The primary of CT should be greater than the Maximum Primary current rounded of to nearest hundred. supposing the maximum primary current is 920 Amps the CT ratio is to be 1000/5 or 1000/1.

Actually, best practice is to size the CT ratio to have the expected normal load fall into the middle of the range. This is where the CT's accuracy is best and most stable under temperature variances. It also allows more head room for overloads. If you put a 920A continuous load through a 1000:5 CT, whenever something inductive turns on it will drive the CT into saturation. So for a 920A normalized load, I would use a 2000:5 CT (or 2000:1 if the WHM needs a 1A input).

Dear sir

Thanks for your comment and well taken, I have mentioned Maximum permissible current as an example for the persons to understand.It was not normal current.

Thanks for the information kind Sirs. I have an additional inquiry.

If I have a total computed load of, for example I = 630A, I could still use the 1000:5 CT rating? (If my meter requires 5A).

Yes, it would work fine, but again, I would opt for a 1200:5 if possible.