A telecom copper cable placed in the vicinity of a power line will suffer electromagnetic perturbation. This will be especially important in the case of monophase lines (railways traction system) as compared to three phase lines (power lines). Signal perturbation, which causes reduction in the signal/noise ratio, could lead to accidents such as aspect change of railway signals. This is why it is essential to measure the screening effect of the cable armoring, represented by the Reduction Factor rk.
The test equipment for the reduction factor complies with the standards while allowing for a variable distance between the loop conductor and the cable under test.