Electric Shower Cable Size Guide (UK)
The right cable size depends on the shower's kW rating, the cable run length and the installation method. Here are the standard sizes we use across Devon for 7.5kW up to 12.5kW showers, all to BS 7671 18th Edition.
| Shower | Current draw | Cable (T+E) | Protection |
|---|---|---|---|
| 7.5 kW | ~32A | 6 mm² | 32A Type C RCBO |
| 8.5 kW | ~37A | 10 mm² | 40A Type C RCBO |
| 9.5 kW | ~41A | 10 mm² | 45A Type C RCBO |
| 10.5 kW | ~46A | 10 mm² | 50A Type C RCBO |
| 12.5 kW | ~55A | 16 mm² | 63A Type C RCBO |
These are baseline figures.
Actual cable size may need uprating for long runs (over ~12 m), cables in insulation, grouped circuits or high ambient temperature. Always have a qualified electrician design and certify the circuit. We never undersize cable to win a quote.
What an electric shower install includes
- Dedicated new circuit from the consumer unit to the shower (10 mm² typical)
- New RCBO in the consumer unit sized to the shower
- Pull cord isolator switch outside the bathroom
- Supplementary bonding check / certification
- Electrical Installation Certificate issued and Building Control notification
Need an electric shower circuit installed?
From £350 plus VAT across Devon. CHAS approved, fully insured.
01626 374 059Frequently Asked Questions
What size cable for an 8.5kW electric shower?
An 8.5kW shower draws around 37A. The minimum cable size is 10 mm² twin and earth, protected by a 40A Type C RCBO. 6 mm² is not adequate for an 8.5kW shower under modern wiring regulations and reference methods used in most UK homes.
What size cable for a 9.5kW electric shower?
A 9.5kW shower draws roughly 41A. We install on 10 mm² twin and earth, protected by a 45A or 50A RCBO depending on the cable run length and installation method. Long runs may need uprating.
What size cable for a 10.5kW electric shower?
10.5kW pulls around 46A. 10 mm² cable on a 50A Type C RCBO is the standard install — but always allow for cable run length, grouping and any insulation derating. Some installs need 16 mm².
Can I use 6mm cable for a 9.5kW shower?
No. 6 mm² is rated around 32–34A in typical clipped or installed conditions, well below the 41A draw of a 9.5kW shower. Using it is dangerous, will likely fail an EICR, and is not compliant with BS 7671.
How much to install or upgrade an electric shower circuit?
A new dedicated shower circuit in Devon typically costs £350–£550 plus VAT depending on cable run length, access and consumer unit space. We give a fixed price after a quick survey.