Why Electric Showers Need a Dedicated Circuit
An electric shower heats water on demand using a resistive element -- the same principle as a kettle, but running continuously for 5 to 15 minutes. An 8.5kW shower draws around 37A. A 10.8kW shower draws around 47A. These loads are far too high to share a ring main or spur circuit -- they need a dedicated radial circuit run directly from the consumer unit, protected by a correctly rated RCBO.
A shower circuit cannot be added to an existing socket ring, spurred from another circuit, or share a cable with any other load. Each shower = one dedicated circuit.
Bathroom Zone Requirements (BS 7671 Section 701)
Bathrooms are a special location under BS 7671:2018 Section 701. The standard defines zones around the bath and shower that restrict what electrical equipment can be installed and where:
| Zone | Area | What's Permitted |
|---|---|---|
| Zone 0 | Inside the shower tray or bath | SELV equipment only (IPX7 or higher) |
| Zone 1 | Above the shower tray up to 2.25m | Shower unit itself, SELV equipment, IPX4 minimum |
| Zone 2 | 600mm outside Zone 1 | IPX4 rated equipment, shaver sockets |
| Outside zones | Beyond Zone 2 | Standard accessories permitted with RCD protection |
No Wall Switches Inside the Bathroom
BS 7671 Section 701 prohibits standard switches within reach of a person using the shower or bath. The shower circuit must be controlled by a ceiling-mounted pull-cord switch (positioned so it cannot be reached from the shower), or by a switch mounted outside the bathroom door. We always fit a 45A double-pole ceiling pull-cord switch directly above the shower enclosure at a safe height.
Cable Size: Matching the Shower's kW Rating
The cable size is determined by the shower's rated current draw, the cable run length, and the installation method. The most common combinations:
| Shower Rating | Current Draw | RCBO Rating | Typical Cable |
|---|---|---|---|
| 7.5kW | ~33A | 32A or 40A | 6mm² T&E |
| 8.5kW | ~37A | 40A | 6mm² T&E |
| 9.5kW | ~41A | 45A | 10mm² T&E |
| 10.8kW | ~47A | 50A | 10mm² T&E |
These are the standard cable sizes for typical domestic installations with short to medium cable runs. For longer runs (over 15 metres from consumer unit to shower), voltage drop calculations may require a larger cross-section even for lower-rated showers. We calculate this from the actual route before ordering materials -- never guess.
Undersized Cable Is a Fire Risk
We regularly encounter existing shower circuits wired in 2.5mm² or incorrectly sized 6mm² cable for a 10.8kW shower -- usually installed by someone who did not check the kW rating or calculate the run length properly. An undersized cable runs hot, degrades over time, and creates a fire risk. If your shower frequently trips the RCBO, this is a likely cause. We can test the existing circuit and advise whether it needs upgrading.
RCBO vs RCD Protection
The shower circuit must be protected by a 30mA RCD. The best approach is an RCBO (combined MCB and RCD) at the consumer unit dedicated to the shower circuit. This means:
- A fault on the shower circuit trips only the shower RCBO -- not the whole house
- The shower is protected for both overload (MCB function) and earth fault (RCD function)
- The shower can be isolated independently for maintenance
Older installations sometimes have shower circuits protected only by an MCB with an upstream RCD. This still provides RCD protection, but a shower fault trips all circuits on that RCD. We always install dedicated RCBOs for new shower circuits.
Electric Shower Installation Cost
| Scope | Typical Cost | Notes |
|---|---|---|
| Like-for-like replacement (existing circuit) | From £120 | Electrical connection only, correct cable already in place |
| New shower circuit (up to 10m run) | From £280 | RCBO, 6mm² or 10mm² cable, pull-cord switch, EIC |
| New circuit (10–20m run) | From £380 | Longer cable run, may need 10mm² regardless of kW rating |
| Upgrade existing underrated circuit | From £250 | Replaces undersized cable and RCBO with correctly rated spec |
| Consumer unit upgrade (if needed) | From £450 | If no spare ways or upgrading from old rewirable board |
Prices are indicative from prices and include labour, materials, testing, EIC, and Part P notification. VAT at 20% applies. Supply of the shower unit itself is not included -- we connect units supplied by the customer or can supply and fit from manufacturer. Fixed written quote provided before any work starts.
Replacing vs. New Installation
Like-for-Like Replacement
If you are replacing a shower that already has a correctly rated dedicated circuit, the electrical work is straightforward -- disconnect the old unit, connect the new one, test the circuit, and issue a Minor Electrical Installation Works Certificate (MEIWC). If the existing circuit cable and RCBO are correctly rated for the new shower's kW rating, no circuit work is needed.
Check the kW Rating Before You Buy
If you are upgrading from an 8.5kW shower to a 10.8kW model, the existing 6mm² cable and 40A RCBO will not be correctly rated for the new load -- the circuit will need upgrading. Tell us the kW rating of your new shower before we quote, and we will check whether the existing circuit is adequate.
New Installation
Installing a shower where none existed before requires a new dedicated circuit from scratch: RCBO at the consumer unit, cable run to the bathroom, ceiling pull-cord switch, and connection to the shower unit. This is fully notifiable under Part P. We carry out a survey to plan the cable route (typically through the void above the bathroom ceiling or in surface trunking if there is no loft access) and provide a fixed quote before starting.
Frequently Asked Questions
Can I fit an electric shower myself?
No. Installing the electrical circuit for an electric shower is notifiable work under Part P of the Building Regulations, in a bathroom special location under BS 7671 Section 701. It must be carried out by a registered electrician. An unregistered installation cannot be self-certified and may invalidate your home insurance.
What size cable does an electric shower need?
An 8.5kW shower on a 40A RCBO typically requires 6mm² twin and earth. A 9.5kW or 10.8kW shower on a 45A or 50A RCBO requires 10mm² twin and earth. The exact size depends on the cable run length. We calculate this from the actual route before ordering materials.
Do I need a new consumer unit for an electric shower?
Only if your existing consumer unit has no spare ways, or if it is an older rewirable fuse board. Most modern consumer units have a spare way for a shower RCBO. We check this during the survey and advise whether a consumer unit upgrade is needed.
What is the pull-cord switch for?
BS 7671 Section 701 requires that switches controlling circuits in bathrooms must not be within reach of someone using the bath or shower. A ceiling-mounted pull-cord switch, positioned out of reach of the shower, is the correct control method. A wall switch at hand height inside the bathroom is not permitted for this circuit.
Why Choose DS Electrical?
- NAPIT Approved -- all work self-certified and notified to Building Control on your behalf
- BS 7671 Section 701 experience -- bathroom special location installations carried out regularly across Somerset
- City & Guilds 18th Edition and 2391 qualified
- CHAS Accredited
- Fixed prices -- written quote before work starts
- Local -- Wells, Shepton Mallet, Bath, Frome, Glastonbury and surrounding villages