What is load testing?
Proving that a CCR holds its set current at every brightness step as the load changes, using a dummy load on the bench or the real circuit on site.
A constant current regulator is built to keep the current steady whatever the load. Load testing proves it. The CCR is run into a known load, a dummy load or load bank on the bench or the real circuit on site, and the output current is read at each brightness step and compared with the value for that step. The load is then changed within the CCR’s rating to confirm that the current stays within tolerance while the voltage follows the load.
The connected load must stay within the CCR’s rated capacity, and the test shows whether the CCR is overloaded or lightly loaded beyond what the manufacturer allows. Because the output can reach a hazardous voltage, the load is connected or changed only with the CCR isolated, locked out and proved dead, and the CCR is never run with an open output.
- Prepare. Get the permit, use a competent person, and gather calibrated instruments and the load plan from the manufacturer.
- Isolate & connect. Lock out and prove dead, then connect the dummy load, or confirm the real circuit is fully connected.
- Energise at the first step. Set the lowest brightness step, let the output settle and read the current.
- Step through. Check the output current at each brightness step against the value for that step.
- Vary the load. Change the load within the CCR rating, with the CCR isolated for each change, and read current and voltage again.
- Compare & record. Compare with the manufacturer’s values and earlier records, log the results, then isolate before disconnecting.
What the readings suggest
Current holds at every step
The CCR is regulating under load. Voltage then follows the load, so compare it with earlier records.
Current falls as load rises
The CCR may be at its limit, overloaded or faulty. Stop, isolate and investigate rather than keep running.
Voltage rises with load
This is expected. Voltage is the result of the current and the total load, so it rises as load is added.
Current drifts at light load
Some regulators hold less well when lightly loaded. Compare with the manufacturer’s guidance on minimum load.
Meter and display disagree
Check the instrument is true-RMS, in range and in calibration, and that both readings use the same step and load.
Always record
Log the load level, step, current, voltage, date and instrument, so changes can be trended over time.
Frequently Asked Questions
Q1What is load testing in airfield ground lighting?
Running a constant current regulator into a known load, either a dummy load or load bank on the bench or the real circuit on site, and checking that it holds its set current at each brightness step as the load changes, while staying within its rating.
Q2Why is a dummy load or load bank used?
It lets a CCR be tested away from the airfield circuit, for example after repair or before delivery. It stands in for the circuit load in a controlled and adjustable way, and it must be suitably rated for the CCR and the test.
Q3What does a load test show?
Whether the output current stays at the value for each step as the load changes, that the voltage rises and falls with the load as expected, and that the CCR is not overloaded. It gives confidence that the CCR will behave correctly on the real circuit.
Q4What load levels are used?
The levels and the tolerances on current are set by the CCR manufacturer, the applicable standard and the aerodrome's procedures, usually from a light load up to the full rated load. They are not given here and must be taken from those documents.
Q5Why must the output never be left open?
A CCR keeps driving its set current. An open output can produce a dangerously high voltage. The load is connected or changed only with the CCR switched off, locked out and proved dead, and the CCR is never run with its output open.
Q6When is load testing carried out?
At factory and site acceptance, after a CCR is repaired or replaced, during commissioning on the real circuit, when fixtures or cable are added or removed so that the load has changed, and when investigating a regulation problem.
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