What Size Cable Do You Need for an 80 Amp Circuit?
For an 80 amp circuit, use 16mm² copper cable under BS 7671 Table 4D5A, rated at 85A clipped direct. Under NEC, 4 AWG at 75°C provides 85A per Table 310.16. For conduit installations, upgrade to 25mm² as the Method B rating for 16mm² drops to 73A, below the 80A requirement.
Quick Reference: Cable Size for 80 Amp Sub-Main Distribution by Standard
| Standard | Cable Size | Conditions | Reference |
|---|---|---|---|
| BS 7671 | 16mm² | Method C (clipped direct), PVC insulation | Table 4D5A |
| NEC | 4 AWG | THWN-2, 75°C column | Table 310.16 |
| AS/NZS 3008 | 16mm² | Clipped direct or in tray, max 30°C ambient | Table 13 |
| IEC 60364 | 16mm² | Reference method C, PVC insulation | Table B.52.4 |
Values shown are for copper conductors in typical domestic/commercial conditions. Actual size depends on installation method, ambient temperature, and cable length. Use our free cable sizing calculator for your exact scenario.
Typical Applications for a 80 Amp Sub-Main Distribution
- Large sub-main distribution
- Commercial building feed
- Industrial panel supply
- Multi-unit residential feed
Calculate Your Exact Cable Size
These are general guidelines. Your specific installation needs exact calculation accounting for cable route length, installation method, ambient temperature, and cable grouping.
Frequently Asked Questions
Is 16mm² enough for 80 amps in conduit?▼
No. 16mm² in conduit (Method B) is rated at only 73A under BS 7671 — below 80A. Use 25mm² in conduit (rated at 89A) or 16mm² XLPE clipped direct (rated at 107A). Installation method significantly affects the required cable size.
What size SWA cable for 80 amps?▼
Use 25mm² SWA cable for an 80A sub-main. 16mm² SWA is rated at approximately 76A in ground — below the 80A requirement. 25mm² SWA provides adequate capacity with margin for derating.
What size earth conductor for an 80 amp circuit?▼
Under BS 7671 Table 54.7, the minimum CPC for 16mm² line conductors is 16mm². If using 25mm² line conductors, the CPC can be 16mm². The adiabatic equation may permit a smaller CPC.
What is 4 AWG equivalent in mm²?▼
4 AWG has a cross-sectional area of 21.2mm², falling between 16mm² and 25mm² in metric sizing. Its NEC ampacity at 75°C is 85A per Table 310.16.
How far can I run 16mm² cable at 80 amps?▼
At 230V with a 5% voltage drop limit, 16mm² cable can run approximately 14m at 80A. For 25mm², the maximum extends to about 22m. Longer sub-main runs require proportionally larger cables.
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