CCR and Circuit
Existing load
Add one row per kind of fixture already on the circuit. Watts are the lamp or fixture power on the secondary side.
| Description | Qty | W each | Total (W) |
|---|
Planned Additions
Fixtures you want to add. Leave empty to see only the spare capacity.
| Description | Qty | W each | Total (W) |
|---|
Report details
Build-up
Method and Worked Example
1. Existing load
With a measured kVA, that value is used directly and the cable and efficiency are only applied to added fixtures.
2. Spare capacity
Spare is measured against the usable capacity, not the nameplate rating.
3. Fixtures that fit
R_add is the resistance of the extra loop cable you enter for each added fixture.
Worked example
| Item | Value |
|---|---|
| 100 × 45 W, #8 AWG, 4,000 m, 6.6 A | 5.64 kVA |
| 10 kVA CCR at 90 % | 9.00 kVA usable |
| Spare capacity | 3.36 kVA |
| More 45 W fixtures | 63 |
| Plus 20 × 45 W planned | 6.69 kVA, 66.9 % |
What this tool does not do
It checks load capacity only. It does not check the maximum circuit voltage, the number of series transformers, cable insulation limits, or how the CCR behaves with lamps out. A measured kVA should be taken at the highest brightness step.
AGL Spare Capacity Calculator: Frequently Asked Questions
Quick answers on the remaining load capacity of a CCR circuit and whether planned fixtures will fit.
What does the AGL Spare Capacity Calculator do?
It works out the remaining load capacity on an existing CCR circuit below your maximum loading. It shows how many more fixtures of a chosen wattage would fit, checks a list of planned additions, and reports the load after additions and the CCR output voltage. It also produces a build-up and a PDF report.
How is the spare capacity calculated?
Spare = rating × maximum loading − Sexisting. It is measured against the usable capacity, not the nameplate rating. For example, a 10 kVA CCR at 90 % has 9.00 kVA usable, and with an existing load of 5.64 kVA the spare capacity is 3.36 kVA.
How is the existing load found?
Either from fixture groups or from a measured kVA. From fixture groups, S = (Σ qty × W ÷ η + I² × Rcable) ÷ PF, which includes transformer efficiency, the cable loss and the power factor. With a measured kVA, that value is used directly, and the cable and efficiency are applied only to added fixtures. A measured kVA should be taken at the highest brightness step.
How many more fixtures will fit?
n = floor(Spare ÷ Seach), where Seach = (W ÷ η + I² × Radd) ÷ PF and Radd is the resistance of the extra loop cable you enter for each added fixture. In the worked example, 100 × 45 W on #8 AWG with 4,000 m of cable at 6.6 A is 5.64 kVA, and 63 more 45 W fixtures fit.
How does it check planned additions?
Enter the groups of fixtures you want to add and the calculator adds their load, including the added cable. In the worked example, 20 × 45 W planned gives a load after additions of 6.69 kVA, which is 66.9 % of the CCR rating. Leave the list empty to see only the spare capacity.
Are the maximum loading, efficiency and power factor standard values?
No. They are planning assumptions and placeholders for your own design rules. The CCR rating is treated as kVA capacity, so check it against your CCR data sheet. Final design shall be verified against manufacturer data and the applicable project specification.
What does the Spare Capacity Calculator not check?
It checks load capacity only. It does not check the maximum circuit voltage, the number of series transformers, cable insulation limits, or how the CCR behaves with lamps out. Use the related calculators, such as Calculator #16 for the required CCR kVA rating and Calculator #13 for series circuit load, for those checks.