Solar Cable Voltage Drop Chart

Use this worksheet after a calculator result from PV string, combiner, inverter, and route screens is known. It records the current basis, conductor material, voltage-drop target, terminal temperature, derating conditions, and listed-equipment checks before a PV conductor choice moves forward.

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Quick reference table

PV cable sizing is a workflow, not a single table lookup. Check the DC source-circuit run with module Isc and the DC voltage-drop calculator, check the inverter output with AC current and the wire size calculator, then close both paths with ampacity, terminal temperature, conduit or rooftop derating, and listed-equipment instructions.

PV conductor workflow documentation

PV conductor workflow documentation
Run segment	Calculator to open	Record before final review
Module string or source circuit	DC voltage drop and solar combiner sizing	Module Isc, string count, source-circuit current, one-way length, conductor material, and DC voltage-drop target
Combiner output or array output circuit	Solar combiner sizing, ampacity calculator, and voltage drop chart	Combined current, continuous-current basis, OCPD review point, raceway route, terminal rating, and derating conditions
Inverter AC output circuit	Wire size calculator and voltage drop calculator	Inverter AC output current, voltage, phase, one-way distance, conductor material, ampacity basis, and voltage-drop target
Equipment termination	Ampacity chart and terminal temperature chart	Allowed conductor material, lug temperature rating, torque instructions, enclosure rating, and manufacturer installation instructions

PV cable review checklist

PV cable review checklist
Review layer	What to document	Why it matters
Current basis	Module Isc, combiner output current, inverter AC output current, and any continuous-current basis used	Wrong current basis makes every downstream conductor and OCPD check unreliable
Voltage drop	DC string voltage or AC output voltage, one-way route length, conductor material, and target percent drop	Long PV routes can lose harvest or reduce equipment voltage even when ampacity passes
Heat and derating	Ambient temperature, rooftop exposure, conduit grouping, current-carrying conductor count, and insulation family	PV conductors can be routed through hot rooftop and raceway conditions that reduce usable ampacity
Listed equipment	Module, combiner, inverter, disconnect, rapid-shutdown equipment, lugs, and cable product data	Listed equipment markings and instructions can be more restrictive than a planning worksheet

Formula basis

DC PV voltage drop check: Vdrop = I x R x 2 x one-way length / 1000. AC inverter-output check: use single-phase or three-phase voltage-drop formula from the wire size calculator.

I is the documented PV current basis: module Isc, combiner output current, or inverter AC output current.
R is conductor resistance for the selected material and size at the calculation basis.
One-way length is the routed path length, including rooftop, attic, wall, and equipment offsets.
The final conductor review still needs usable ampacity, terminal temperature, conductor-count adjustment, ambient correction, and equipment listing data.

Worked examples

DC string route checkA roof source circuit starts with module Isc and route length. Use the DC voltage-drop calculator for percent drop, then carry the same current basis into ampacity, rooftop, conduit, and equipment-listing review.

Inverter AC output checkAfter inverter sizing, use the inverter AC output current with the wire size calculator. Record phase, voltage, conductor material, distance, terminal basis, and whether ampacity or voltage drop controls the result.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

This worksheet is an educational planning estimate and does not reproduce NEC conductor, ampacity, or PV tables.
Voltage-drop targets are project-performance criteria unless the adopted code, contract, utility, equipment instruction, or AHJ makes a specific value mandatory.
Final PV conductor choices depend on the adopted NEC edition, equipment listings, manufacturer instructions, utility requirements, local amendments, and AHJ review.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Verify PV source-circuit current, overcurrent protection, conductor ampacity, terminal temperature, rooftop or ambient correction, conduit grouping, equipment listings, rapid-shutdown equipment, utility rules, adopted NEC requirements, and AHJ expectations before installation.
Do not copy worksheet values directly into permit drawings without checking the module, combiner, inverter, disconnect, cable, raceway, and lug data for the actual listed equipment.

How to use this chart

1Separate DC and AC runsStart by labeling whether the run is a PV source circuit, combiner output, battery-side DC run, or inverter AC output run because each path uses different calculator inputs.

2Carry the same current basisRecord module Isc, source-circuit current, combiner output current, or inverter AC output current before moving between voltage-drop, ampacity, and wire-size screens.

3Close with equipment dataBefore the result is treated as job-ready, verify terminal temperature, conductor material, cable type, conduit route, rooftop exposure, listed equipment, utility requirements, and AHJ expectations.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Map the routeWrite the physical route for each PV conductor segment, including roof, attic, wall, equipment pad, disconnect, combiner, and inverter offsets.
Run the linked calculatorsUse DC voltage drop for source or battery-side DC runs, wire size for inverter AC output runs, and ampacity for temperature, conductor count, and termination limits.
Record the controlling factorMark whether the selected conductor was controlled by ampacity, voltage drop, terminal temperature, derating, equipment listing, or a project-specific instruction.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Using inverter AC current for a DC source-circuit run or module Isc for the inverter AC output run.
Checking voltage drop but skipping terminal temperature, conductor-count adjustment, ambient heat, rooftop routing, or equipment listing data.
Treating a planning worksheet as final PV code approval without checking adopted NEC requirements, utility review, manufacturer instructions, and AHJ expectations.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Should PV cable sizing be a separate calculator?

For this worksheet, the safer workflow is a PV worksheet connected to existing calculators. DC source circuits use the DC voltage-drop and combiner tools; inverter AC output circuits use the wire size, voltage-drop, and ampacity tools. The worksheet keeps the PV documentation visible without pretending to replace listed-equipment or AHJ review.

Which current should I enter for PV voltage drop?

Use the documented current basis for the run being screened. For a module source circuit, use module Isc with the required source-circuit review. For inverter AC output, use the inverter output current from the inverter data or sizing result.

Can voltage drop control PV conductor size?

Yes. A conductor can pass ampacity and still be increased because the PV route is long, the voltage is low, the run is sensitive, or the project uses a tight harvest-loss target.