For a device with operational isolation, the continuous working voltage that can be applied across the device in normal operation must be less than 42.5 V_RMS or 60 V_DC.

If the device is expected to function correctly with more than 42.5 V_RMS or 60 V_DC applied continuously across the isolation barrier, then the circuitry on both sides of the barrier must be regarded as operating at an unsafe voltage, and further isolation or insulation systems must form a barrier between these circuits and any user-accessible circuitry according to safety standard requirements.