Earth leakage currents in lighting circuits depend on the quality of all system components and on the circumstances (humidity, dust, age). With respect to luminaires, IEC 598 restricts these currents to 0.5 or 1 mA, depending on the insulation classification.The earth connection may consist of an earth lead or the capacitance between the luminaire and its surroundings.
The earth leakage current of a ballast normally is very low: all ballasts undergo a high-voltage insulation test of 2500 V to check their insulation resistance.This can be checked in practice with a Megger (Megohm meter) of minimum 500 V DC, resulting in an insulation resistance of more than 2 Megohm.Tests with burning lamps can give earth leakage currents of about 1 to 2 mA per lamp circuit. In older installations these values can be somewhat higher due to humidity, dust, cable capacity or during the starting period. But the earth leakage current never should be higher than 5 mA per lamp circuit.
There are two different applications for earth leakage devices:
1)to protect people from direct contact with live parts, reacting to the current through the human body; there are 10 and 30 mA devices,
2)to protect people and grounded installations, reacting to the direct current to earth; there are devices of 300 mA and higher.
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Fault finding
When a lighting installation becomes inoperative, a complex, thorough, trouble-shooting procedure may prove overly time-consuming. In many cases, a simple check of the power switches, lamps and gear may provide the quickest response to the problem. In some cases, however, it may be necessary to isolate the problem systematically and perform complete electrical tests in order to restore the lighting properly. Besides, it is important to know if the installation or individual isolated lighting points did function well before the failure.
There are four basic causes of failures:
A:lamp-related: not starting, cycling, too bright or dim,
B:gear-related: too hot or damaged ballast, capacitor, starter,
C:installation-related: cable too hot, terminals or lampholder damaged, blown fuses, contactors or circuit breakers switched,
D:supply-voltage-related: too high, too low, wrong frequency, bad voltage waveform.
There are also four basic trouble-shooting methods:
1.visual inspection,
2.quick fix for restoring lighting,
3.trouble-shooting checklist,
4.electrical tests.
1A:Visual inspection of lamps
End-of-life of lamps is characterized by low light output and/or different colours.Visual signs include blackening at the ends of the arc tube and electrode tip deterioration.
Additional checks:
-broken lamp pins,
-broken or loose electrodes in lamp tube,
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