| differences of potential normally existing between conductors and between conductors and earth as follows:
a) Extra-low voltage: not exceeding 50 V a.c. or 120 V ripple-free d.c.
b) Low voltage: exceeding upper limits of extra-low voltage, but not exceeding 1 000 V a.c. or 1 500 V d.c.
c) High voltage: exceeding upper limits of low voltage |