The length of the unshielded input/output circuit conductors between the product and the coupling/decoupling network (s) shall be less than or equal to 6.5 feet (2 m). If it is specified in the manufacturer’s installation instructions that input/output circuit shall only be connected with shielded cables, then in these cases, the transients shall be applied directly (i.e. without the 40 ohm series resistor) to the shield of a 65.5 ft (20 m) length of shielded cable. Current compensated chokes may be used to decouple input/output circuits carrying high frequency signals, to reduce attenuation problems