PV Cable Sizing & Voltage Drop Guide
A practical buyer guide for choosing 4mm2, 6mm2, and 10mm2 solar DC cable, estimating voltage drop, and preparing a clean RFQ for H1Z2Z2-K or PV1-F cable orders.
Cable size
Choose conductor cross-section based on current, route length, installation method, and loss target.
Voltage drop
Estimate DC loss before ordering cable, especially on long rooftop and ground-mount runs.
RFQ clarity
Specify standard, voltage, color, length, packing, and document needs to avoid quotation gaps.
Quick Answer: 4mm2 vs 6mm2 vs 10mm2 PV Cable
For many rooftop projects, 4mm2 and 6mm2 are the main options. 4mm2 can be economical on short string runs, while 6mm2 gives lower resistance and more design margin. 10mm2 is usually selected when route length, string current, or energy-loss economics justify the higher material cost.
| Cable Size | Copper Resistance Reference | Common Use | Buyer Note |
|---|---|---|---|
| 4mm2 | 4.61 ohm/km | Short residential strings, compact rooftop cable runs | Cost-efficient, but check voltage drop on longer runs or hot roofs. |
| 6mm2 | 3.08 ohm/km | Residential and C&I strings, longer rooftop runs | Common upgrade when buyers need lower voltage drop or higher current margin. |
| 10mm2 | 1.83 ohm/km | Long DC runs, utility strings, combiner feeder sections | Higher material cost; useful when cable loss or run length becomes critical. |
Resistance values are planning references for copper conductors near 20 C. Final ampacity and voltage drop must be checked against datasheet, installation method, ambient temperature, grouping, and local electrical code.
PV DC Voltage Drop Formula
Voltage drop = 2 x L x I x R
L is one-way cable length in meters, I is string current in amps, and R is cable resistance in ohms per meter. The factor 2 accounts for the positive and negative conductor path in a DC circuit.
Step 1: Estimate voltage drop in volts
Use the full conductor path. For example, a 40 m one-way rooftop run is 80 m total conductor path for DC voltage drop.
Step 2: Convert to percentage
Voltage drop percentage = voltage drop in volts / operating string voltage x 100. Higher string voltage usually reduces the percentage loss for the same cable run.
Worked Examples for Buyers
| Scenario | Cable | Length | Current | Voltage | Result | Action |
|---|---|---|---|---|---|---|
| Short rooftop string | 4mm2 | 30 m one-way | 13 A | 600 V | Approx. 0.60% voltage drop | Usually acceptable if local code and datasheet ampacity are satisfied. |
| Longer residential run | 4mm2 | 60 m one-way | 13 A | 600 V | Approx. 1.20% voltage drop | Review 6mm2 if the project target is close to 1% or roof temperature is high. |
| C&I rooftop string | 6mm2 | 80 m one-way | 16 A | 900 V | Approx. 0.88% voltage drop | Good starting point for many 1000V/1500V commercial layouts. |
| Long combiner feeder | 10mm2 | 120 m one-way | 20 A | 1000 V | Approx. 0.88% voltage drop | Often justified when route length and energy loss matter more than cable cost. |
Do Not Size Cable by Price Alone
A cheaper 4mm2 cable can become more expensive over the project life if it causes higher energy loss or fails local design checks. A larger cable can also be unnecessary if the run is short. The right decision balances cable price, energy yield, installation method, temperature, and documentation requirements.
PV Cable RFQ Checklist
A clear RFQ reduces back-and-forth and helps the supplier quote the correct cable, packing, and documents from the start.
Related PV Cable Products
H1Z2Z2-K 4mm2 PV Cable
Common residential and short-run rooftop solar cable option.
H1Z2Z2-K 6mm2 PV Cable
Common upgrade for longer runs, hotter roofs, or lower voltage drop targets.
H1Z2Z2-K 10mm2 PV Cable
Used when long runs or feeder sections require lower resistance.
PV1-F 4mm2 PV Cable
Alternative cable option when the project specification calls for PV1-F.
PV Cable Sizing FAQ
Is 4mm2 or 6mm2 PV cable better for rooftop solar?
Both can be suitable depending on current, string length, installation method, temperature, and local code. 4mm2 is common for short residential strings, while 6mm2 is often selected for longer runs, higher current modules, hotter roofs, or lower voltage drop targets.
How do I calculate DC voltage drop for a PV string?
For a two-conductor DC circuit, voltage drop can be estimated as 2 x one-way cable length x string current x cable resistance per meter. Divide the voltage drop by the string operating voltage to get the percentage voltage drop.
What voltage drop target should buyers use for PV DC cable?
Many project teams target around 1% to 2% voltage drop on DC string runs, but the acceptable value depends on project economics, local design practice, inverter MPPT range, cable cost, and installation constraints.
What information should be included in a PV cable RFQ?
Include conductor size, standard, rated voltage, color, length per roll or pre-cut length, connector requirement, packaging, target market documents, quantity, destination port, and inspection requirements.
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