Main cable cross-section dimensioning factors
Definition : Nominal current of circuits
The total circuit power must be analysed and calculated:
lamp power consumption;
any lamp ballast or transformer losses.
Depending on the type of load and any compensation, a power factor must be applied. A poor power factor, for example, can double the current flowing through the circuits.
For sizing electrical distribution, one should allow for the fact that the lamps consume 1.5 to 2 times their nominal current:
at end of life for all lamps;
during the long preheating phase for high-intensity discharge lamps.
Definition : Single-phase or three-phase distribution with or without neutral
In most buildings used for tertiary or commercial purposes, the lighting system is distributed via a single-phase circuit. To optimise the cabling, especially for highpower
applications over large areas, three-phase distribution is sometimes used: 230 V between phase and neutral or between phases, or 400 V between phases for high-power lamps (2000 W).
Definition : Length of electrical distribution
The cable resistance induces a voltage drop proportional to the cable length and the current. It can cause malfunctions when the lamps are switched on or reduce the luminosity in steady state.
The length of the circuits and the distributed power require an appropriate cable cross-section.
Definition : Conductive material
Copper is less resistive but more expensive than aluminum. The use of aluminum is reserved for high-current electrical distribution.
