Secondary CT Leads

The CT leads are not very long because the way the CTs are constructed, that being an enameled wire wound on a laminated silicon-iron core. From the bushing to the junction box the current wire needs insulation but the enamel isn't enough. Is easier and safer to use factory insulated wire (cable) than to try to insulate the leads in the manufacturing process for a transformer.

No, it won't affect the CT's performance. However, it may affect yours. The CT junction box usually does not have terminal blocks, or even much space to make terminations to the CT secondary wires. It is also usually located very close to the energized transformer bushings, where you don't want to go near. That is why the manufacturer brings the CT wiring to the CT terminal box, so that you have a place where you can easily access the CT wiring even when the transformer is energized. The CT wiring is brought to terminal blocks (usually of shorting terminal type) where you can do external wiring at a safe distance from the energized transformer terminals.

Caution!!!! NEVER open circuit a CT secondary when it is energized on the primary! That is why the manufacturer should provide shorting terminal blocks, so the secondary can be short-circuited if there were any need to make a change in the external wiring while energized. However, it is always preferred to de-energize the transformer when working on the CT circuits.