The rating factor is one of the most important factors when it comes to CTs. The rating factor (RF) of CTs implies the maximum continuous current that can flow through the CT primary without exceeding the thermal capability of its windings.
The typical values of rating factors for CT range from 1.0 to 4.0.
A CT having RF of 4.0 having a secondary rating of 5 A can produce up to 20 A of secondary current.
Similarly, A CT having RF of 2.0 having a secondary rating of 5 A can produce up to 10 A of secondary current.
While implementing measurement circuits the RF of CT should and must be kept in mind.
Also see: Working and construction of CT