List your circuits once and get the transformer quantities, connected load, cable loss, kVA and CCR size for each, as a schedule you can export.
A circuit load schedule is the table a design or tender package hangs from. For each series circuit it carries the fixture count, the isolating transformers behind them, the load including transformer and cable losses, and the CCR that serves it. Enter the circuits and the schedule, the transformer count by size and the cable by conductor build themselves.
Applied to every circuit.
Power factor of the transformer and lamp load. Cable loss is treated as resistive.
Planning assumption. See Calculator #18.
A transformer is sized so the fixture watts stay within this share of its rating.
Conductor resistance is corrected from 20 °C.
One row per series circuit. Cable length is the total primary cable laid for the loop, out and back. The example circuits are placeholders to overwrite.
| Circuit | Description | Fixtures | W each | Transf. per fixture | Cable loop (m) | Conductor |
|---|
| Circuit | Description | Fixtures | Transf. | Size (W) | Fixture load (kW) | Transf. loss (kW) | Cable loss (kW) | Load (kW) | kVA | Output (V) | Required (kVA) | CCR | Loading (%) |
|---|
| Size (W) | Quantity |
|---|
| Conductor | Length (m) |
|---|
Every step is shown so a line can be checked by hand. It follows the same method as the CCR Capacity calculator.
Quantity is fixtures times transformers per fixture. The size is the smallest standard size whose rating, at your loading limit, covers one fixture's watts.
Fixture watts are divided by the transformer efficiency, then the cable loss is added. Cable resistance comes from the conductor value corrected for temperature.
Cable loss is resistive, so only the transformer and lamp load carries a reactive part.
Growth is added and the result is divided by the maximum loading. The CCR is the smallest standard size at or above that figure. Above 30 kVA the circuit is shown as a split. Standard CCR sizes are treated as kVA capacity.
| Item | Value |
|---|---|
| 120 × 45 W, 90 % transformers | 6.00 kW |
| 6,000 m of 6 mm² at 20 °C | 18.48 Ω |
| Cable loss, 6.6 A | 0.805 kW |
| Load | 6.805 kW |
| At PF 0.95 (vector sum) | 7.085 kVA |
| Output voltage | 1,073 V |
| × 1.10 ÷ 0.90 | 8.659 kVA |
| CCR | 10 kVA, 70.8 % loaded |
| Transformers | 120 × 45 W |
It does not check voltage drop on the secondary cables, split a circuit across CCRs for you, or account for different conductor sizes within one circuit. Fixture watts, transformer efficiency and the allowances are inputs, and the example circuits shown at the start are placeholders to overwrite.
Quick answers on how the circuit load schedule, transformer quantities and CCR sizes are worked out.
You list each series circuit once and the tool builds the schedule. For each circuit it gives the fixture count, the isolating transformer quantity and size, the connected load including transformer and cable losses, the kVA, the output voltage and the CCR that serves it. It also totals the transformers by size and the cable by conductor, and exports the schedule as a PDF or CSV.
The quantity is fixtures × transformers per fixture. The size is the smallest standard size whose rating, at your loading limit, covers one fixture's watts, so Size ≥ Wfixture ÷ loading limit. In the worked example, 120 × 45 W fixtures at a 90 % transformer loading limit need 120 × 45 W transformers.
P = n × W ÷ η + I² × Rcable, where Rcable = r20 × (1 + 0.00393 × (T − 20)) × length ÷ 1000. Fixture watts are divided by the transformer efficiency and the cable loss at the circuit current is added. For example, 6,000 m of 6 mm² at 20 °C is 18.48 Ω, which gives a cable loss of 0.805 kW at 6.6 A and a load of 6.805 kW.
S = √(P² + Q²), with Q = (n × W ÷ η) × tan(cos⁻¹ PF), and V = S ÷ I. The cable loss is resistive, so only the transformer and lamp load carries a reactive part. In the worked example, at a power factor of 0.95 the vector sum is 7.085 kVA and the output voltage is 1,073 V.
Required = S × (1 + growth) ÷ maximum loading, and the CCR is the smallest standard size at or above that figure. In the worked example, 7.085 kVA × 1.10 ÷ 0.90 is 8.659 kVA, so a 10 kVA CCR is chosen at 70.8 % loaded. Standard CCR sizes are treated as kVA capacity, and above 30 kVA the circuit is shown as a split.
No. The series current, power factor, transformer efficiency, loading limit, CCR expansion allowance, maximum CCR loading and cable temperature are inputs you set, and the example circuits are placeholders to overwrite. Each circuit is treated as one CCR, and the cable length is the total primary cable laid for the loop, out and back.
It does not check voltage drop on the secondary cables, split a circuit across CCRs for you, or account for different conductor sizes within one circuit. The schedule shall be checked against the approved layout, cable schedule and manufacturers' data before issue.
Please read before relying on any content on this page or on any result or record produced by it.