Electric Shower Installation
An electric shower is a heavy continuous load in a special location — the install is about cable size, RCD protection and getting the bathroom zones right.
An electric shower is one of the highest continuous loads in a home, and it sits in a bathroom, so it combines a demanding cable calculation with the special-location rules of Section 701. Getting both right is what makes the job compliant.
This guide covers sizing the shower circuit, selecting cable and protection, providing isolation, and applying the bathroom-zone requirements.
Key takeaways
- Shower load is continuous and high — a 9.5 kW shower draws around 41 A, so cable size matters.
- 10 mm² cable on a 40/45 A device is common, but confirm against the actual rating and install method.
- The circuit needs 30 mA RCD protection as a bathroom circuit.
- Provide a means of isolation — a pull-cord or an accessible switch outside the zones.
- Apply Section 701 zones: the shower unit and switching must suit their position and IP rating.
Sizing the circuit
Work out the shower's current from its power rating — a 9.5 kW unit at 230 V is roughly 41 A, and units up to 10.5 kW are common. Because the load is continuous, there's no diversity to apply; the cable and device are sized for the full current.
10 mm² cable protected by a 40 A or 45 A device is typical, but a long run, loft insulation or bunching can push the cable size up, so size it for the specific installation rather than assuming.
No diversity here
Unlike a cooker, a shower runs at full load the whole time it's on — size the cable and protection to the full current.
Protection and isolation
As a bathroom circuit, the shower needs 30 mA RCD additional protection. Provide a means of isolation local to the shower — commonly a ceiling-mounted pull-cord double-pole switch rated for the load, or a switch positioned outside the zones.
Make sure the isolation switch rating matches the shower current; an underrated pull-cord is a common defect.
Bathroom zones
The shower is in a special location, so Section 701 zoning applies. The shower unit itself must be suitable for its position, switching must not be within reach of a person using the bath or shower unless it's a suitably rated cord-operated switch, and IP ratings must match the zone.
Check the main protective bonding and whether supplementary bonding can be omitted under the usual conditions.
Testing and certification
Test the circuit — continuity, insulation resistance, polarity, Zs and RCD operation — and confirm the disconnection time is within limits for the device and earthing arrangement.
A new shower circuit is notifiable under Part P and certified with an EIC.
Certify the shower circuit
TradePlanr's EIC records the shower circuit, RCD and full test schedule ready to sign before you leave.
Frequently asked questions
What cable size for an electric shower?
10 mm² on a 40 A or 45 A device is common for showers up to around 9.5–10.5 kW, but it depends on the exact rating, the installation method and volt drop. Long or insulated runs may need a larger cable.
Does a shower circuit need an RCD?
Yes. As a circuit serving a bathroom, an electric shower requires 30 mA RCD additional protection under BS 7671.
Do I apply diversity to a shower?
No. A shower runs at its full rated load the whole time it's used, so there's no diversity — size the cable and protective device for the full current.
From guidance to action
Related guides
Special Locations (Part 7) Explained
Why Part 7 exists, the locations it covers, and how bathroom zones and supplementary bonding work.
Cable Sizing to BS 7671
The full cable sizing method — design current, correction factors, tabulated ratings and volt drop.
Main Protective Bonding Explained
What main protective bonding does, conductor sizes, and where bonding is required to BS 7671.
