Understanding cable standards for low voltage conductors in high voltage environments
Maybe the problem here is that the UL voltage of 600V printed on the jacket of a cable does always mean that the inside individual wires are capable to have 600V difference in voltage to each other. It automatically means an insulation withstanding at least 600V to the outside of the jacket. Those who demand the value of 600V printed on the jacket should reconsider their request. The insulation voltage of a (signal) cable's multiple inside low voltage wires to the cable's outside is only mentioned in the cable's specification, but never printed on the jacket, since it would be misleading.