Aluminum (NAYY) vs Copper (NYY) Cable Sizing Equivalency and Bimetallic Al-Cu Termination
0.6/1 kV NAYY aluminum vs NYY copper underground feeder cross-section equivalency chart, galvanic corrosion physics, and friction-welded bimetallic Al-Cu lug rules.
NAYY 0.6/1 kV aluminum power cables are widely used across underground utility feeders, solar PV collector runs, and industrial sub-mains where lower weight over NYY copper cables simplifies pulling. Because aluminum's conductivity (`γ_Al ≈ 35`) is roughly 61% that of copper (`γ_Cu ≈ 56`), matching ampacity requires stepping up 1–2 standard IEC 60228 cross-sections and terminating with bimetallic (Al-Cu) lugs.
> Related Category: Compare underground feeders and lugs in NAYY Aluminum Cables, NYY Cables, and Aluminum Cable Lugs.
Copper (NYY) to Aluminum (NAYY) cross-section equivalency chart
Based on the `56 ÷ 35 ≈ 1.60` DC resistance ratio and IEC 60364-5-52 underground ampacity tables (always verify `%ΔU` voltage drop on long runs per our Cable Current-Carrying Capacity & Sizing Guide):
| Copper NYY size (`Cu`) | Equivalent Aluminum NAYY size (`Al`) | Typical buried ampacity (20 °C, PVC) | Conductor mass reduction |
|---|---|---|---|
| 16 mm² Cu | 25 mm² Al | ~95 – 102 A | ~50% lighter |
| 25 mm² Cu | 35 mm² Al | ~120 – 127 A | ~55% lighter |
| 35 mm² Cu | 50 mm² Al | ~145 – 151 A | ~55% lighter |
| 50 mm² Cu | 70 mm² Al | ~180 – 190 A | ~55% lighter |
| 70 mm² Cu | 95 or 120 mm² Al | ~220 – 250 A | ~48–55% lighter |
| 95 mm² Cu | 150 mm² Al | ~270 – 280 A | ~50% lighter |
| 120 mm² Cu | 185 mm² Al | ~305 – 320 A | ~52% lighter |
| 150 mm² Cu | 240 mm² Al | ~345 – 365 A | ~50% lighter |
Remember to upsize conduit diameter, bending radius, and panel cable glands to match the larger outer diameter of the upsized NAYY feeder. For LSZH fire-safe installations, compare PVC vs XLPE sheaths in NYY vs N2XH Cable Difference.
Why bare aluminum must never clamp directly to bare copper
- Galvanic corrosion: In humid air, copper (`+0.34 V`) and aluminum (`-1.66 V`) form an electrochemical cell that corrodes the anodic aluminum conductor into high-resistance white powder.
- Insulating oxide skin (`Al₂O₃`): Freshly stripped aluminum oxidizes within seconds into a hard, electrically insulating film.
- Thermal expansion & cold creep: Aluminum expands ~38% more than copper under load cycling, relaxing clamping pressure inside copper-only lugs until arcing begins.
Safe termination rules: Bimetallic Al-Cu lugs and oxide-inhibiting compound
- Onto copper busbars or MCCB palms: Crimp a friction-welded bimetallic (Al-Cu) cable lug—its barrel is pure aluminum (often pre-filled with oxide-breaking grease) while its palm is solid copper, keeping the dissimilar-metal transition sealed inside a solid-state factory weld.
- Onto aluminum busbars or Al-to-Al joints: Use dedicated aluminum cable lugs, wire-brush the stripped strands, apply oxide-inhibiting joint compound immediately, and crimp with matched aluminum hexagonal dies (see DIN Rail Terminal Block & Cable Lug Guide).
- Inside box terminals: Only use breaker or DIN-rail terminals explicitly stamped `Al/Cu` (tinned alloy bodies) torqued with a calibrated wrench.
Frequently asked questions
Can copper and aluminum wires be twisted together inside a junction box?
Never. Twisted Cu–Al splices overheat and ignite due to galvanic corrosion and thermal creep; transition strictly via friction-welded bimetallic splice sleeves or `Al/Cu`-listed mechanical connectors.
Is 0.6/1 kV NAYY suitable for direct burial?
Yes. Like NYY, NAYY has a heavy black PVC outer sheath rated for direct trench burial on a sand bed beneath mechanical warning tape.
What copper NYY size replaces a 4×50 mm² NAYY aluminum feeder?
In thermal ampacity and loop resistance, `4×50 mm²` aluminum NAYY corresponds closely to `4×35 mm²` copper NYY.
Why isn't aluminum wire used for 1.5 mm² or 2.5 mm² branch sockets?
Small-gauge solid aluminum fractures easily at bends and creeps loose in standard residential screw sockets; building regulations restrict aluminum power conductors to ≥16 mm² feeder circuits.