Required CCR kVA rating for a series circuit, with expansion allowance, maximum loading, smallest standard size and spare capacity.
Start from the circuit load, add cable loss, allow for future fixtures, and divide by the loading you are willing to run the regulator at. The result is the rating you need, the smallest standard CCR that covers it, and how much room is left on that CCR.
Full-brightness power from the manufacturer's data sheet.
Maximum (full-brightness) series current, normally 6.6 A. Used for cable loss and rated voltage.
Used for the fixtures option only. Planning assumption.
Power factor of the transformer and lamp load (cable loss is treated as purely resistive). Planning assumption.
Extra load you want to be able to add later. Your project's own allowance.
Highest share of the CCR rating you will design to. Your project's own rule, not a standard value.
Standard nominal CCR ratings are treated as kVA capacity, which is the conservative reading (FAA ratings are quoted in kW, IEC in kVA). Confirm against the manufacturer's rating.
| Item | Value | Basis |
|---|---|---|
| Enter a valid load on the Calculate tab. | ||
Transformer efficiency, power factor, expansion allowance and maximum loading are planning assumptions. Standard CCR sizes are treated as nominal kVA capacity.
Quick answers on sizing the required CCR kVA rating for a series circuit.
It works out the required CCR kVA rating for a series circuit, with an expansion allowance and a maximum loading. It starts from the circuit load, adds cable loss, allows for future fixtures, and divides by the loading you are willing to run the regulator at. The result is the rating you need, the smallest standard CCR that covers it, and how much room is left on that CCR.
There are three ways. You can enter fixtures as quantity times watts, the known real load in kW excluding cable, or the known total load in kVA with everything included. With the known total, cable loss is assumed to be already included, so the cable inputs are ignored.
Real power is the number of fixtures times watts divided by transformer efficiency, plus the cable loss of current squared times cable resistance. The reactive power is the transformer-side real power times the tangent of the arccosine of the power factor, and the apparent power combines the real and reactive parts as a vector sum. Cable loss is resistive, so it carries no reactive part.
The future load is the present load times one plus the expansion allowance, which scales the whole present load, cable loss included. The required rating is the future load divided by the maximum CCR loading you set. Both the allowance and the maximum loading are your project's own rules, not standard values.
The smallest standard size at or above the required rating is selected, and the spare capacity is the rating times the maximum loading minus the present load, which still contains the expansion allowance. A 30 kVA CCR at 6.6 A is about 4.5 kV, so the next size up would exceed 5 kV, which is beyond standard 5 kV series cable, so the load is split across circuits. Sizes are treated as nominal kVA capacity, which is the conservative reading because FAA ratings are quoted in kW and IEC ratings in kVA.
100 fixtures of 45 W at 90 percent efficiency give 5,000 W, with 359 W of cable loss on 4,000 m of #8 AWG at 6.6 A. At a power factor of 0.95 the vector sum is 5.61 kVA, and 6.17 kVA with 10 percent expansion. At 90 percent maximum loading the required rating is 6.85 kVA, so the smallest standard CCR is 7.5 kVA, loaded 75 percent now and 82 percent after expansion. The spare above the present load is 1.14 kVA, which fits 21 extra fixtures, but that figure includes the 10 percent expansion allowance. With the allowance kept, 0.58 kVA is left, which fits 10 extra fixtures.
It is approximate. The count holds cable loss constant, and it is available with the fixtures option only. Treat it as a planning figure.
It does not model brightness steps, lamp-out conditions, CCR efficiency or input supply sizing. A lightly loaded CCR can perform poorly, so check the manufacturer's minimum-load guidance too. The sizes offered are nominal and your CCR data sheet governs, so final design shall be verified against the CCR manufacturer's rating and loading guidance.
Every step is shown so the result can be checked by hand.
Fixture power divided by transformer efficiency, plus cable loss, then combined with the reactive power of the load to give apparent power. Cable loss is resistive, so it carries no reactive part.
If you know the real load or the total kVA already, enter it directly.
The CCR should carry the future load without exceeding the maximum loading you set.
The smallest standard size at or above the required rating is selected. Spare capacity is what remains below the maximum loading. A 30 kVA CCR at 6.6 A is about 4.5 kV, so the next size up would exceed 5 kV, which is beyond standard 5 kV series cable, so the load is split across circuits.
The first spare is measured from the present load, so it includes the expansion allowance. The second shows what is left once that allowance is kept.
| Item | Value |
|---|---|
| 100 fixtures × 45 W at 90 % | 5,000 W |
| #8 AWG, 4,000 m, 6.6 A | 359 W cable loss |
| Total at PF 0.95 (vector sum) | 5.61 kVA |
| With 10 % expansion | 6.17 kVA |
| At 90 % max loading | 6.85 kVA required |
| Smallest standard CCR | 7.5 kVA |
| Loading now / after expansion | 75 % / 82 % |
| Spare to max loading | 1.14 kVA |
| Extra fixtures that fit | 21 |
| Spare after 10 % expansion | 0.58 kVA |
| Extra fixtures, expansion kept | 10 |
It does not model brightness steps, lamp-out conditions, CCR efficiency or input supply sizing. A lightly loaded CCR can perform poorly, so check the manufacturer's minimum-load guidance too. The sizes offered are nominal, and your CCR data sheet governs.
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