Conductors for low-voltage installations

As the high temperatures associated with the operation of low-voltage halogen lamps place severe demands on lamp holder conductors, a skilful combination of conductor and insulation is essential. Tin-plated copper conductors with silicone insulation are recommended for temperatures of up to 180 °C at the cable´s conductor; nickel-plated copper cables with polytetrafluoroethylene (PTFE) sheathing are recommended for temperatures of up to 250 °C. Welded connections ensure the most effective heat discharge. Control measurements should be carried out if other connection types are used, e.g. crimping or plug connectors. To prevent the risk of additional heat generation, the maximum permissible current load must be observed when dimensioning the conductor cross-section. When using electromagnetic transformers, the conductor resistance causes a relatively large voltage drop. This drop in voltage is always associated with a reduction of luminous flux. For instance, an 11 % drop in voltage will lead to a 30 % drop in luminous flux. For this reason, care should be taken to ensure secondary conductors are kept as short as possible and conductor cross-sections are adequately dimensioned when wiring luminaires. Nevertheless, transformers should not be mounted too near the light source (> 25 cm clearance if possible) to prevent the heat generated by the lamp from raising the ambient temperature above the critical level for a transformer.
As electronic converters operate at high frequencies, consideration must be taken of the skin effect, i.e. the displacement of the electrons from the middle of the conductor to its surface. As a result, the full cross-section of the conductor is no longer used, the resistance increases and the voltage drops. In addition, the alternating current resistance, which is caused by the inductance of the feed line, can result in an even greater voltage drop. It is therefore recommended that lamp conductors be laid closely parallel or twisted together.

Voltage losses (V) from a two-metre secondary conductor
Working frequency
Load W
Cross-section mm²
0,75
1
1,5
50 Hz ( electromagnetic transformers)
50
0,38
0,29
0,2
any wiring layout
100
0,74
0,56
0,39
40 kHz (electronic converters)
50
1,4
1,25
1,2
any wiring layout (loops)
100
3,3
3,1
3
40 kHz (electronic converters)
50
0,5
0,45
0,35
wires twisted together or closely parallel
100
1,2
1
0,85
Conductors for installations with halogen lamps
All conductors must be selected to suit the luminaire conditions (see table) in terms of material, cross-section and insulation. Testing these conductors under unfavourable conditions is essential as the commonly occurring high temperatures considerably reduce the conductivity of the conductor and hence its current-carrying capacity.
Insulation
Conductor
Cross-section
Mains voltage
Max. temperature
Material
mm²
V
°C
Si
Cu tin-plated
0,75
300
180
PTFE
Cu nickel-plated
0,75
500
250
PTFE
Cu nickel-plated
1
500
250
PTFE
Ni
1
500
250
PTFE
Ni
1,5
500
250