What is circuit loading?
How full the regulator is. The same circuit can leave a CCR comfortably loaded, nearly full or barely used, and each state has its own problems.
Load calculation finds how many watts a circuit draws. Circuit loading asks the next question: against the regulator’s rating, how much is that? It is the load as a share of what the CCR can deliver, normally checked at the highest step.
1Too light and too heavy are both problems
A regulator is built to work within a range. Very light loading can leave it with poor power factor and less accurate regulation, depending on the design. Very heavy loading leaves no margin, and a regulator pushed past its rating cannot hold the current, so the lights dim. The goal is the middle.
| Loading | What it means | Action |
|---|---|---|
| Light | Far below rating: power factor and regulation accuracy can suffer, depending on design | Check the manufacturer's minimum loading; consider a smaller CCR or combining circuits |
| Design range | Comfortably inside the rating with room to grow | The aim for a new circuit |
| Near the limit | Little or no margin: one more fixture or longer cable can overload it | Plan a larger CCR, or split the circuit |
2Loading does not stay put
It rises when fixtures are added or cable is extended, and falls when fixtures fail or are replaced by lower-power types. An LED retrofit shows the catch: the fixtures draw far less, but the cable loss is unchanged at the same current, so the load does not fall in proportion. In the example, loading drops from 49% to 22% and may now be too light.
3Manage it by design and by checking
Size the CCR so the day-one loading sits in the design range with room to grow. Re-check it after every change to the circuit, including retrofits and repairs. If a circuit is too light, a smaller regulator or a combined circuit may suit; if it is too heavy, split the circuit or fit a larger regulator.
- Take the load. Use the circuit load at the highest step from the load calculation.
- Divide by the rating. Compare like with like, kW with kW or kVA with kVA, to get the loading as a percentage.
- Compare with the design range. Not too light, not near the limit.
- Check light loading. Confirm the CCR still regulates well, using the manufacturer’s minimum.
- Re-check after changes. Added fixtures, longer cable, retrofits, failures.
- Adjust. Split, combine or resize the circuit if loading has left the range.
| Term | Meaning |
|---|---|
| Circuit loading | Circuit load as a percentage of the CCR rating |
| Circuit load | Total power the circuit draws, from the load calculation |
| CCR rating | kW or kVA the regulator is built to deliver at rated current |
| Minimum loading | Lowest load at which the CCR still meets its specification |
| Design range | Loading band that leaves room for growth without running too light |
| Circuit splitting | Dividing fixtures between regulators to bring loading back in range |
Frequently Asked Questions
Q1What is circuit loading?
How much of a constant current regulator's rated capacity the series circuit actually uses, usually shown as a percentage of the regulator's kW or kVA rating at the highest step.
Q2How is it different from load calculation?
Load calculation finds how many watts the circuit draws. Circuit loading divides that figure by the regulator's rating to show how full the regulator is, and so whether it is well matched.
Q3What is wrong with a very light load?
A regulator run far below its rating can have poor power factor, more waveform distortion and less accurate current regulation, depending on its design. Check the manufacturer's stated minimum loading.
Q4What is wrong with a very heavy load?
There is no room for added fixtures, ageing or measurement error, and if the load grows past the rating the regulator cannot hold the current. The lights dim and the regulator may alarm.
Q5Why can an LED retrofit make loading worse?
LED fixtures draw far less than halogen lamps, so the load falls. But the cable loss stays the same at the same current, so the circuit may drop below the regulator's comfortable range.
Q6How does loading change over time?
It rises when fixtures are added or cable is extended, and falls when lamps are replaced by lower-power types or fixtures fail. Check it again after any change to the circuit.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.