How is a cable's voltage rating defined, and what key parameters characterize its electrical withstand capabilities?

A cable's voltage rating denotes the maximum electrical potential it can continuously sustain while meeting performance standards, typically expressed through dual values (U₀/U) representing phase-to-earth and phase-to-phase voltages respectively. These ratings—such as 0.6/1kV or 19/33kV configurations—employ RMS (Root Mean Square) measurements critical for alternating current systems, unlike direct current applications which utilize peak voltage specifications. The rating system incorporates three core parameters: U₀ (insulated conductor to ground potential), U (conductor-to-conductor potential), and Uₘ (maximum system voltage, often shown in parentheses).   Notably, direct current applications typically utilize 1.5x the alternating current rating, with specifications like BS 6724's 600/1000V AC cables suitable for 900V DC to ground or 1800V between conductors. This classification framework ensures compatibility across diverse electrical systems while accounting for insulation performance under sustained voltage stress.