What Size Cable Do You Need for an Electric Shower?
For an electric shower, use 6mm² cable for models up to 8.5kW (37A at 230V) on a 40A circuit, or 10mm² for 9.5-10.5kW models (41-46A) on a 45A or 50A circuit. All electric showers require a dedicated radial circuit with an appropriate MCB or RCBO.
Quick Reference: Cable Size for Electric Shower by Standard
| Standard | Cable Size | Conditions | Reference |
|---|---|---|---|
| BS 7671 | 6mm² (8.5kW) or 10mm² (10.5kW) | Dedicated radial circuit, Method C | Table 4D1A |
| NEC | 8 AWG (40A circuit) | Dedicated circuit, instantaneous water heater | Table 310.16 |
| AS/NZS 3008 | 6mm² or 10mm² | Dedicated circuit, AS/NZS 3000 | Table 13 |
| IEC 60364 | 6mm² or 10mm² | Dedicated circuit per IEC 60364 | 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 Electric Shower
- 8.5kW electric shower
- 9.5kW electric shower
- 10.5kW electric shower
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
Can I use 6mm² for a 10.5kW shower?▼
No. A 10.5kW shower draws approximately 46A at 230V. 6mm² cable clipped direct is rated at 47A — too close to the load with no margin for derating. Use 10mm² on a 50A circuit for a 10.5kW shower.
What MCB size for an electric shower?▼
For 8.5kW (37A): 40A MCB with 6mm² cable. For 9.5kW (41A): 45A MCB with 10mm² cable. For 10.5kW (46A): 50A MCB with 10mm² cable. Always use Type B MCB for resistive shower loads.
Does an electric shower need an RCD?▼
Yes. Under BS 7671 Regulation 411.3.3, all circuits in bathrooms require 30mA RCD protection. Most modern consumer units provide this via an RCBO or RCD-protected MCB.
How far can I run shower cable?▼
On 10mm² cable at 46A (10.5kW), the maximum run for 5% voltage drop is approximately 15m. For 6mm² at 37A (8.5kW), maximum is about 18m. Most bathroom circuits are well within these limits.
Can I spur an electric shower off a ring main?▼
Absolutely not. An electric shower must have its own dedicated radial circuit from the consumer unit with an appropriately rated MCB/RCBO. Connecting to a ring final circuit is dangerous and non-compliant.
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