Electrical reference chart
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.
Quick reference table
PV cable sizing is a workflow, not a single table lookup. Screen the DC source-circuit run with module Isc and the DC voltage-drop calculator, screen 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 handoff
| 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
| 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 |
How to use this chart
Separate DC and AC runs
Start 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.
Carry the same current basis
Record module Isc, source-circuit current, combiner output current, or inverter AC output current before moving between voltage-drop, ampacity, and wire-size screens.
Close with equipment data
Before 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.
Formula basis
DC PV voltage drop screen: Vdrop = I x R x 2 x one-way length / 1000. AC inverter-output screen: 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 screen
A 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 screen
After 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.
Related calculators
DC Voltage Drop Calculator
Calculate voltage drop for DC circuits including solar, battery, automotive, and low-voltage systems. Critical for sizing conductors in 12V, 24V, 48V, and other DC applications.
Wire Size Calculator
Calculate NEC-style wire sizes from load current, ampacity basis, and voltage-drop targets
Wire Ampacity Calculator
Calculate conductor ampacity with temperature correction, conductor-count adjustment, and 60°C or 75°C termination checks
Solar Combiner Sizing Calculator
Screen PV source-circuit current, string OCPD review points, combiner output current, and inverter input-current warnings from module Isc and parallel strings.
Inverter Sizing Calculator
Screen solar PV inverter AC size, DC/AC ratio range, and cold-weather string counts from module data.
Related charts
Voltage Drop Chart
Use this voltage drop chart: 3% equals 3.6 V at 120 V, 7.2 V at 240 V, and 14.4 V at 480 V; 5% equals 6 V, 12 V, and 24 V.
Wire Size Chart
Screen conductor size from calculated load, copper or aluminum material, terminal rating, derating, voltage drop, and equipment notes.
Ampacity Chart
Review conductor ampacity as a heat problem: material, insulation, terminal rating, ambient correction, bundling adjustment, and equipment limits.
Solar Combiner Sizing Chart
Use a solar combiner sizing chart to document module Isc, parallel strings, source-circuit current, string fuse review, output current, and equipment follow-up.
Inverter Sizing Chart
Use an inverter sizing chart to document array kWdc, target DC/AC ratio, module Voc and Vmp, cold-weather string voltage, MPPT window, and inverter follow-up.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.