How do you troubleshoot several fixtures failing at once?
One dark light points to the fixture. Several failing together point to the circuit, and the pattern of which lights are out shows what kind of circuit fault to look for.
On a series circuit with isolation transformers the loop stays complete when one fixture fails, so one dark light points at the fixture. If several fixtures fail together, suspect the circuit, not the fixture. The pattern shows which fault. Every second light dark means one interleaved circuit is out, usually an open circuit or a CCR problem. Lights beyond a point dark while those before it stay lit suggests a short circuit that bypasses the rest of the loop, with the CCR seeing a smaller load. Scattered lights dark with the loop complete points to a common cause such as water in pits, connector faults, surge damage or ageing sources.
Several lights dim together points to the step setting, or to leakage or heavy loading that stops the CCR delivering its current, so the CCR output current is read first. ATC is told, the CCR is switched off, isolated and locked out, and the circuit is proved dead and earthed as the site procedure requires before anything is touched. The outage is reported (for example by NOTAM) as the authority requires. The loop is then split into sections and tested by continuity or insulation resistance. If the circuit and transformers are healthy, each affected fixture is checked on its own side: secondary, connector, then the fixture. After repair the circuit is retested and the findings recorded.
Frequently Asked Questions
Q1Why are several failed fixtures treated differently from one?
On a series circuit with isolation transformers the loop stays complete when one fixture fails, so one dark light points to the fixture side. If several fixtures fail together, the cause is suspected in the circuit, not in the fixtures.
Q2What does it mean if every second light is dark?
Lights in a zone are often interleaved across two circuits, so losing one circuit leaves every second light lit instead of a gap in the pattern. The dark lights are on the circuit that has failed, usually an open circuit or a CCR problem, found from the CCR alarm and output.
Q3What if the lights beyond a certain point are dark and the ones before it are lit?
That pattern suggests a short circuit. Current takes the shortcut and bypasses the rest of the loop, so fixtures before the short usually stay lit and those beyond it go dark. The CCR sees a smaller load and holds its current at a lower voltage.
Q4What if several scattered lights are dark but the loop is complete?
A common cause is likely rather than a break in the loop. Water in pits, connector faults, surge damage and ageing light sources are checked, and each affected fixture is then tested on its own side, starting with the secondary and the connector.
Q5Why would several lights be dim together?
Dim lights point to the brightness step setting, or to leakage or heavy loading that stops the CCR delivering its current. The CCR output current is read at the selected step before the fixtures are blamed.
Q6What is done before any fixture or circuit is touched?
ATC is told, the CCR is switched off, isolated and locked out, and the circuit is proved dead and earthed as the site procedure requires. The loop is then divided into sections and tested by continuity or insulation resistance. After repair the circuit is retested and the findings recorded.
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