What is circuit expansion?
Adding fixtures, transformers and cable to an existing series circuit — only as far as the CCR’s rating allows.
Circuit expansion is adding fixtures, isolation transformers or cable to an existing series circuit, such as when a taxiway is extended. Because every addition is in series on the same loop, it adds to the circuit’s load and cable length.
The total load after expansion must stay within the rating of the CCR, with spare capacity left. The new section is tied in only with the circuit isolated, locked out and proved dead, then the extended loop is tested and its readings recorded as the new baseline. If there is no headroom, the new lighting goes on a new circuit or a larger CCR.
- Check headroom. Existing load plus the addition must stay within the CCR rating, and the longer loop within its output voltage.
- Decide. Extend the circuit, or use a new circuit or CCR if there is no headroom.
- Isolate. CCR off, locked out and tagged; confirm the circuit is dead.
- Connect. Tie the new cable and transformers into the loop in series.
- Test. Continuity, insulation, and rated current with every fixture lit.
- Record. New baseline readings; update drawings and the zone map.
Frequently Asked Questions
Q1What is circuit expansion in airfield lighting?
Adding fixtures, isolation transformers or cable to an existing series circuit, for example when a taxiway is extended or extra lights are installed, instead of building a new circuit for them.
Q2What must be checked before expanding a circuit?
That the total load after the addition, made up of the lamps or LEDs, the isolation transformers and the extra cable, is still within the rating of the CCR serving the circuit, with spare capacity left. The extra cable and transformers also raise the voltage the CCR must supply, which must stay within its output voltage capability, and the circuit must keep operating at the same current and brightness steps.
Q3What if the CCR has no spare capacity?
The new lighting goes on a new circuit, normally with its own CCR, or the existing CCR is replaced with a larger one. Putting the new fixtures on their own zone also keeps faults and control separate.
Q4How is the new section connected?
With the circuit isolated, locked out and proved dead. The new primary cable is jointed or connected into the loop, with each new transformer connected in series, following the manufacturer's instructions and the site's permit-to-work procedure.
Q5What testing follows an expansion?
Continuity and insulation resistance tests on the extended loop, then a check that the circuit runs at its rated current and every new fixture lights at each brightness step. The results are compared with the design values.
Q6Why is the baseline updated?
Adding cable and transformers changes the loop's resistance and loading, so the old commissioning values no longer apply. The new readings are recorded as the baseline, and drawings and the zone map are updated, so later tests and fault finding compare against the right figures.
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