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5
3.18 Circuit breakers, fusing and earth leakage
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.
3 19
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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