Circuit & Load Basis
Fixture Load Groups
| Group | Quantity | Watts each (W) | At transformers |
|---|
Primary Cable Loss
Margins & CCR Choice
Report Details
Every Size Compared
| CCR | Rated voltage | Loaded now | After expansion | Spare to max | Status |
|---|
Loading by Brightness Step
| Step | Current | Load | Share of CCR | % now | % with expansion | Voltage needed | vs rated |
|---|
Load by Group
| Group | Quantity | Watts each | At transformers | Share of fixtures |
|---|
How the CCR is selected and loaded
Every step is shown so the result can be checked by hand. For a quick rating on its own, CCR Capacity (#16) follows the same sizing logic. This tool adds the size-by-size comparison and the brightness-step loading.
1. Real load
Fixture watts are divided by the transformer efficiency, then the primary cable loss at full current and any other load are added.
2. Apparent load and expansion
Cable loss is resistive, so it carries no reactive part. This is the same treatment as Calculator #16.
3. Required rating and selection
The CCR must carry the future load without passing the maximum loading you set. The smallest ticked standard size at or above that rating is recommended. Beyond the largest size the load is split across circuits. A size is only recommended if its rated output voltage (kVA ÷ class rated current) stays within 5 kV: at 6.6 A that excludes 50 kVA, while on a 20 A circuit 50 kVA is acceptable.
Each size is then given a status: above 5 kV circuit rating, overloaded, above the maximum now, expansion exceeds the limit, lightly loaded, or suitable.
4. Loading at each brightness step
The fixture load is scaled by the step current ratio raised to a power n (2 for constant impedance, 1 for linear, 0 for constant power). Cable loss always scales with I².
The rated output voltage is the CCR kVA divided by full current. If a step needs more voltage than that, the table flags it. This mostly affects constant-power loads at low current.
Worked example
| Item | Value |
|---|---|
| 80 × 45 W + 24 × 100 W at 90 % | 6,667 W |
| #8 AWG, 4,000 m, 6.6 A | 359 W cable loss |
| Real load | 7,026 W |
| Apparent load at PF 0.95 (vector sum) | 7.36 kVA |
| With 10 % expansion | 8.10 kVA |
| At 90 % max loading | 9.00 kVA required |
| Smallest standard CCR | 10 kVA |
| Loading now / after expansion | 74 % / 81 % |
| Rated voltage / voltage needed | 1,515 V / 1,115 V |
| Spare to max loading | 1.64 kVA |
| Extra fixtures that fit | 24 |
| Spare after 10 % expansion | 0.90 kVA (13 fixtures) |
| Step B1 (2.8 A) / B5 (6.6 A), I² scaling | 13 % / 74 % |
What this tool does not do
It does not model lamp-out conditions, CCR efficiency or input power factor at low steps, or input supply sizing. Real lamp and LED behaviour varies by product, so the step scaling is an approximation. Isolating transformer no-load losses do not fall with current, so real loading at low steps is usually somewhat higher than shown. A lightly loaded CCR can perform poorly, so check the maker's minimum-load guidance. The sizes offered are nominal, and the CCR data sheet governs.