What is extension cable?
When you take compensating Cable?

Extension cable is defined according to IEC 584-3 as original thermal material (from 0 ° C to 200 ° C) with an accuracy class 1 (± 1.5 ° C) or class 2 (± 2.5 ° C).

Compensating cable is an alloy, which behaves in the temperature range of 0 ° C to 100 ° C, similar to the original thermal material, but only with the class 2 (± 2.5 ° C) according to IEC 584-3.