The light line fulfils two functions: first, it provides a sturdy in-line mounting rail on which to fix the electrical units, and second, it provides a housing for the electrical cables that bring power to the units. All the light-line sections are made of hot-dip galvanized steel with a white or silver finish and available in lengths of 1, 2 and 3 electrical units 36 and 58 W.A flat ribbon cable (5 or 7 wires) or two flat ribbon cables (2 x 5 or 2 x 7 wires) are integrated in the light line and guarantee (in combination with an integrated phase selection switch and contact blocks) safe and correct cabling. The 7-wire cable is used to integrate light regulation or emergency lighting for those electrical units that are equipped with emergency battery packs. Double wiring (2 x 5 or 2 x 7 wires) is needed to provide a completely separate mains supply to the electrical units. Double wiring is mostly used for emergency lighting by central emergency batteries or separate switching. Hence, no extra contact blocks or wiring are required.