Choose the smallest primary cable conductor that keeps voltage drop, I²R loss, CCR output voltage and loading inside your limits.
Enter the circuit current, load and cable length, and the tool tests every conductor size on the list. It shows which sizes pass, which check fails on the ones that do not, and the longest run each size can serve. Temperature is applied to the resistance, so the result holds at your worst-case conductor temperature.
Highest series current the circuit will run, normally full brightness.
Fixture and isolating transformer load, without the primary cable. Take it from Calculator #13.
Of the fixtures and transformers, not the cable. Planning assumption.
The series current flows along the whole loop, so the loop cable is what counts.
Covers slack, joints and a future extension. It is added to the length.
Use the worst-case operating temperature. Copper resistance rises about 0.393 % per °C above 20 °C.
Insulation rating from the cable data sheet. Enter 0 to skip this check.
Your project's own design limit, not a standard value.
Also a project limit. Applied to the circuit load in kW.
Combined factor for ambient temperature, grouping and burial, from the cable data sheet. It applies only to sizes with an allowable current entered in the conductor data.
Resistances are nominal DC values at 20 °C. Replace them with your cable data sheet figures. Untick a size that is not stocked or not approved. Enter an allowable current to switch on the current-carrying check for that size.
| Use | Conductor | R at 20 °C (Ω/km) | Allowable current (A) |
|---|
The whole loop re-run in each conductor, from smallest to largest. The chosen size is highlighted.
| Conductor | R (Ω) | Drop (V) | Drop (%) | Loss (W) | Loss (%) | CCR out (V) | Loading | Max loop (m) | Result |
|---|
Every conductor goes through the same four checks. The smallest size that passes all the active ones is chosen.
The resistance per metre comes from the nominal value at 20 °C, corrected for temperature, then multiplied by the loop cable length including allowance.
The series current is the same everywhere, so the drop and the loss follow directly. They are compared with the load voltage and the load power.
The cable drop adds to the real part of the load voltage, and the load's reactive part stays as it is. The CCR must supply the phasor sum, and the cable insulation rating has to cover it.
If you enter an allowable current for a size, the circuit current is compared with it after the derating factor. Sizes with no allowable current are not checked on this point.
Each check gives its own longest loop length. The smallest of the three is the governing one, and it is shown in the table.
Here ρ is the resistance per metre at the conductor temperature.
| Item | Value |
|---|---|
| Current, load, power factor | 6.6 A, 5 kW, 0.95 |
| Loop cable, conductor temperature | 4,000 m, 40 °C |
| Load voltage (S ÷ I) | 797 V |
| 10 mm² Cu: R, drop | 7.895 Ω, 6.53 % |
| #6 AWG Cu: R | 5.591 Ω |
| #6 AWG Cu: drop | 36.9 V (4.63 %) |
| #6 AWG Cu: cable loss | 244 W (4.87 %) |
| #6 AWG Cu: CCR output | 833 V |
| Selected at 5 % and 5 % limits | #6 AWG Cu |
It uses nominal DC resistance and ignores cable reactance, skin effect, secondary cable tails, connectors and brightness steps. It does not check short-circuit withstand, earth-fault loop or mechanical strength, and it does not choose the cable insulation class. Where the circuit uses more than one conductor size in a run, size each section with Calculator #15.
Quick answers on how the smallest primary cable conductor is chosen against voltage drop, loss and CCR output.
It tests every conductor size on your list against the circuit current, load and cable length, and chooses the smallest size that keeps voltage drop, I²R loss, CCR output voltage and loading inside your limits. It shows which sizes pass, which check fails on the ones that do not, and the longest run each size can serve. It also produces a conductor comparison and a PDF report.
Every conductor goes through the same four checks: voltage drop, cable loss, CCR output voltage against the cable's rated voltage, and current loading. The smallest size that passes all the active checks is chosen. The rated-voltage check is skipped if you enter 0, and the current-loading check applies only to sizes with an allowable current entered.
R = R20 × [1 + 0.00393 × (T − 20)] × L ÷ 1000, using the loop cable length including allowance. The series current is the same everywhere, so Vdrop = I × R and Ploss = I² × R. The drop is compared with the load voltage (S ÷ I) and the loss with the load power.
The series current flows along the whole loop, so the loop cable is what counts. You can enter the total loop cable (out and back) or a one-way route length, which is doubled for the loop. The allowance covers slack, joints and a future extension and is added to the length.
The cable drop adds to the real part of the load voltage and the load's reactive part stays as it is, so VCCR = √[(P ÷ I + Vdrop)² + (Q ÷ I)²]. The CCR must supply that phasor sum, and the cable insulation rating has to cover it.
With 6.6 A, 5 kW and a power factor of 0.95 on a 4,000 m loop at 40 °C, the load voltage is 797 V. A 10 mm² Cu cable has R = 7.895 Ω and a 6.53 % drop, so it fails a 5 % limit. #6 AWG Cu has R = 5.591 Ω, a drop of 36.9 V (4.63 %), a cable loss of 244 W (4.87 %) and a CCR output of 833 V, so #6 AWG Cu is selected at 5 % and 5 % limits.
No. The maximum voltage drop and maximum cable loss are your project's own design limits, not standard values. The conductor resistances are nominal DC values at 20 °C, so replace them with your cable data sheet figures, and untick any size that is not stocked or not approved. The current derating factor combines ambient temperature, grouping and burial from the data sheet.
It uses nominal DC resistance and ignores cable reactance, skin effect, secondary cable tails, connectors and brightness steps. It does not check short-circuit withstand, earth-fault loop or mechanical strength, and it does not choose the cable insulation class. Where a circuit uses more than one conductor size in a run, size each section with Calculator #15. Final design shall be verified against the cable manufacturer's data and the project specification.
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