Same physics, six rulebooks. The table compares units, method, limits and — the part that surprises people — whether the limit is a recommendation or law. *NEC figures become binding under energy codes, fire pump rules and adopting specs.
| Standard | Units | Method | Limit | Status | Source |
|---|---|---|---|---|---|
| NEC (US) | AWG · feet | Ch.9 Tbl.8 R / K-factor | 3% / 5% | Recommended* | NFPA 70 |
| CEC (Canada) | AWG · feet | Same physics as NEC | 3% / 5% | Mandatory | CSA C22.1, Rule 8-102 |
| BS 7671 (UK) | mm² · meters | mV/A/m, Appendix 4 | 3% lighting / 5% other | Verified at certification | BS 7671 App. 4 |
| AS/NZS (AU/NZ) | mm² · meters | 3Ø mV/A/m (×1.155 for 1Ø) | 5% total | Mandatory | AS/NZS 3000 + 3008.1 |
| IS 732 (India) | sq mm · meters | IEC method | 4% default; 3%/5% common | Per spec | IS 732:2019 / IEC |
| IEC 60364 | mm² · meters | ρ/A metric | 4% default | Informative | 60364-5-52 Annex G |
Every method on this page reduces to Vd = (factor) × I × L × R, differing only in units, tabulation style and the percentage you're held to. This site runs the AWG engine for NEC/CEC work and the metric engine for the IEC family — pick your standard above and the right calculator, limits and conventions are preset.
Working across borders? The AWG ⇄ mm² converter translates the hardware, and the comparison rows above translate the law.