While bgautreau is technically correct concerning "rating factor", you must still take into account your transformer ratio.
In your case a 2000:5 CT is a 400 to 1 ratio, so when it is used on a 4000A service it will provide an output of 10A. Your measuring equipment may not be able to deal with this large of a value.
The rating factor should only be used to allow for momentary overcurrents (i.e. motor start-up)which do not need to be be measured accurately
