4mm² and 6mm² are the two cable sizes that appear most often in PV string wiring. For most rooftop strings under 15m one-way, 4mm² H1Z2Z2-K is the practical default. For longer runs, higher-current modules or voltage-drop-sensitive designs, 6mm² is the right choice.
The decision should come from a current and voltage-drop calculation — not from habit or simply copying a previous project BOM.
Current capacity: what each size handles
4mm² H1Z2Z2-K has a rated ampacity of approximately 32A free-air (IEC 60364-5-52 reference), but in PV practice the continuous design current from a typical string is 10–14A Isc. At these levels, 4mm² is thermally adequate for most installations. 6mm² provides headroom for higher-current modules (Isc above 13–15A) or installations in high ambient temperatures where derating applies.
Voltage drop: when 6mm² pays for itself
For a 1000V string with 10A Isc and 30m one-way run: 4mm² gives approximately 1.5% voltage drop; 6mm² drops that to around 1.0%. On a 15m run, 4mm² is well within the typical 1–2% design limit. Once the one-way run exceeds 25–30m, or module Isc is above 13A, running a voltage-drop calculation before specifying is worth the five minutes — 6mm² often pays for itself in recovered generation and fewer inspection questions.
Cost and BOM considerations
6mm² cable costs approximately 30–50% more per metre than 4mm². On a 100-panel rooftop project, upgrading from 4mm² to 6mm² across all string cables typically adds USD 150–400 depending on run lengths and market. On a ground-mount project with 50m+ home-run cables, the yield improvement from lower resistive losses often justifies the additional cost.
Certificate by destination market
The cable standard you specify must match the destination market. The wrong standard or jacket marking can hold a shipment at customs or fail an installation inspection, even when the conductor size is correct.
- EU / IEC projects: EN 50618 and IEC 62930 (H1Z2Z2-K); TÜV mark commonly requested
- Australia: IEC / TÜV cable used to AS/NZS 5033 installation rules
- USA: UL 4703 PV Wire — a different construction, not interchangeable with H1Z2Z2-K
- EU in-building runs: confirm CPR reaction-to-fire class (e.g. Cca / Eca)
- Always confirm red/black colour split, printed marking and reel length before order
Ampacity & voltage-drop comparison (4mm² / 6mm² / 10mm²)
| Cable size | PV design current (typical) | Approx. VD @ 30 m, 1000 V, 10 A | Best for |
|---|---|---|---|
| 4 mm² | Up to ~11–14 A Isc | ~1.5% | Short rooftop strings, one-way run ≤15–20 m |
| 6 mm² | Up to ~16–18 A Isc | ~1.0% | Longer runs 20–40 m, higher-Isc modules |
| 10 mm² | Up to ~24–27 A Isc | ~0.6% | Home runs, combiner-to-inverter, 1500 V utility |
Ampacity based on IEC 60364-5-52 free-air reference; derate for ambient temperature and installation method (conduit, tray, bundled). Voltage drop is indicative — always confirm with a project-specific calculation before specifying.
Procurement decision table
| Decision area | Buyer question | Procurement check | Risk control |
|---|---|---|---|
| Product scope | Which items are affected by 4mm² vs 6mm² Solar Cable: Which Size for Your PV Project?? | H1Z2Z2-K Solar Cable, PV Cables | Choosing by habit without checking run length |
| Specification input | What must be stated before comparing quotes? | String current (Isc × 1.25 for fuse sizing) | Use the same specification wording across supplier quotes. |
| Commercial input | What makes the quote operationally useful? | One-way run length to combiner or inverter | Tie quantity, packing and destination to the same RFQ line. |
| Quality gate | What should be checked before shipment? | PV Cable Sizing Guide | Ignoring home-run cables from combiner to inverter |
BOM and RFQ context
4mm² vs 6mm² Solar Cable: Which Size for Your PV Project? is most useful when it is read as a sourcing decision, not only an informational article. The affected product scope normally includes H1Z2Z2-K Solar Cable, PV Cables. A buyer should connect the answer to a live BOM, because cable size, connector rating, protection device choice, box configuration, storage accessories and export packing can change together.
For a comparison page, the value is in showing when each option is suitable, not declaring one universal winner. The practical choice depends on voltage class, current rating, installation environment, certificate requirements and the rest of the BOS package. In an RFQ, the minimum inputs should include String current (Isc × 1.25 for fuse sizing), One-way run length to combiner or inverter, Voltage drop target (typically ≤1–2%), Ambient temperature and installation method. These inputs let a sourcing team compare suppliers on the same basis instead of only comparing unit price.
The related follow-up content is PV Cable Sizing Guide, BOS 1500V Selection Guide. Use those pages to validate standards, sizing, inspection and packing before sending a final quote request. The main risk to avoid is: Choosing by habit without checking run length Ignoring home-run cables from combiner to inverter This structure makes the page easier for AI systems to cite because the answer, decision logic and next procurement step are all visible in the main content.