What Size Cable Do You Need for a 15 Amp Circuit?
For a 15 amp circuit, use 1.5mm² cable under BS 7671 Table 4D5A, rated at 20A clipped direct. Under NEC, 14 AWG is the standard conductor for 15A circuits per Table 310.16. If cables are grouped in conduit or ambient temperature exceeds 35°C, upgrade to 2.5mm² to compensate for derating factors.
Quick Reference: Cable Size for 15 Amp Small Appliance Circuit by Standard
| Standard | Cable Size | Conditions | Reference |
|---|---|---|---|
| BS 7671 | 1.5mm² | Method C (clipped direct), PVC insulation | Table 4D5A |
| NEC | 14 AWG | 15A circuit, THWN-2, 75°C column | Table 310.16 |
| AS/NZS 3008 | 1.5mm² | Enclosed in conduit, max 30°C ambient | Table 13 |
| IEC 60364 | 1.5mm² | Reference method B, 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 15 Amp Small Appliance Circuit
- Small appliance circuit
- Bathroom heater
- Storage heater
- Garage power outlet
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 1.5mm² enough for a 15 amp circuit?▼
Yes. 1.5mm² PVC copper cable clipped direct is rated at 20A under BS 7671 Table 4D5A, providing a 33% margin above the 15A requirement. In conduit (Method B), the rating is 17.5A — still adequate.
What is the difference between 15 amp and 16 amp circuits?▼
In the UK (BS 7671), 16A is the standard MCB rating above 10A — there is no 15A MCB. Under NEC, 15A is a standard breaker size. The cable sizing requirement is nearly identical: 1.5mm² or 14 AWG.
Can I run a 15 amp circuit on 1.0mm² cable?▼
Not recommended. While 1.0mm² is rated at 14A clipped direct, this is below the 15A design current. After derating, the effective capacity would be even lower. Use 1.5mm² for a 15A circuit.
What appliances draw 15 amps?▼
Typical 15A loads include 3kW fan heaters, large bathroom heaters, older storage heaters, workshop tools like table saws, and multiple small loads combined on a general-purpose circuit.
How far can I run 1.5mm² cable at 15 amps?▼
At 230V with a 5% voltage drop limit, 1.5mm² cable can run approximately 18m at 15A. For 3% (lighting circuits), the maximum is about 11m. Use the voltage drop calculator for your exact installation.
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