Helpful video reference. We use Nick Bundy's practical installation video "Installing a Shower Cable — Electrician" from his N Bundy Electrical channel. Nick is a NAPIT-registered electrician from Staffordshire and one of the UK's most-watched electrical YouTubers. His video shows the cable-running process clearly — the routing decisions, the consumer unit work, and how a tidy installation looks in practice.
1. Start with the shower's power rating
The data plate on your shower, or its installation manual, will give a power rating in kilowatts. Common ratings are 7.5 kW, 8.5 kW, 9.5 kW, 10.5 kW, and in some cases 12 kW. The power rating determines the design current (I = P/V, so a 9.5 kW shower at 230 V draws about 41.3 A) and therefore the cable and protective device needed.
For most showers up to about 10.5 kW, 10 mm2 twin and earth (6242Y flat cable) is the standard choice. Above that, 16 mm2 may be needed, and the incoming supply fuse at the meter tails also needs checking to confirm the supply can cope.
2. Choosing the right protective device
The shower circuit needs a dedicated MCB or RCBO at the consumer unit. An RCBO is preferred because it provides both overcurrent protection and 30 mA RCD protection in a single device — BS 7671 requires RCD protection for circuits in bathrooms. A 40 A or 45 A type B RCBO is typical for a 9.5 to 10.5 kW shower wired in 10 mm2.
If the existing consumer unit is a split-load type with a single main RCD on one side and all bathroom circuits are already on that side, a plain MCB may be acceptable — but an RCBO removes any ambiguity about protection.
3. Planning the cable route
The cable run is usually from the consumer unit, up through the ceiling void or loft space, and back down into the bathroom wall, entering the shower unit from the top or side. A shorter run means less voltage drop and a simpler installation. Longer runs need a voltage drop calculation to confirm they are within the 3% limit for this type of circuit.
Where the cable passes through or is adjacent to thermal insulation, the current-carrying capacity drops significantly — by more than half in some configurations. This is one reason why an electrician who knows how to apply the derating factors from BS 7671 Table 4C1 and 4C2 is important here.
4. Fixing and clipping the cable
The cable must be mechanically protected and fixed at the correct intervals. Where it runs on the surface of a wall or ceiling, oval conduit or flat metal trunking are the tidy options. Where it passes through joists, a steel plate is required if the cable is within 50 mm of the top or bottom of the joist, to protect against nails from above or below.
In a bathroom the cable must be routed and installed to the zone requirements in BS 7671 Section 701. Cables in the walls are typically in a protected zone directly above or below a socket or switch.
5. The consumer unit connection
The electrician will turn off the main switch, fit the new RCBO, connect the new neutral to the neutral bar, the earth to the earth bar, and the live to the RCBO. On a modern consumer unit this is straightforward. On an older wiring centre or fuse box, there may not be a spare way, or the enclosure may not accept an RCBO at all — in which case a new consumer unit is the right answer, not a bodged connection.
The consumer unit work is the part of this job where the greatest care is required. Even with the main switch off, the meter tails feeding the board remain live — always.
6. Connecting the shower unit
Strip the conductors to the length specified in the shower's installation manual. Brown goes to L, blue to N, green/yellow to E. Tighten to the manufacturer's torque figure — under-tightened terminals in a high-current circuit cause heat, which causes fires. The outer sheath of the cable must be gripped by the cord clamp inside the unit, not the inner conductors.
A double-pole isolating pull cord switch in the ceiling, or a double-pole rocker switch outside the bathroom, allows the shower to be isolated locally without going to the consumer unit. Fit one if the manufacturer specifies it or if there is not already one in place.
7. Testing and certification
Before power is applied: insulation resistance tests between live and earth and between live and neutral (at 500 V DC), continuity of the protective conductor, and polarity checks. These are not optional — they are required by BS 7671 and are the basis for the installation certificate. Once the tests pass, the circuit is energised and tested under load.
The Electrical Installation Certificate is then issued. If the electrician is registered with NICEIC, NAPIT, or a similar approved body, they self-certify and notify the local authority on your behalf. If not, you must notify Building Control separately, which involves an inspection fee and possibly a delay.
When to call us
Shower circuits are one of the most common first-fix jobs Richard carries out across Sandwich and east Kent. Typical work takes half a day: planning the route, running the cable, fitting the RCBO, connecting the shower, testing, and issuing the certificate. A fixed quote before the job starts, and the Part P self-certification is included.
Need a shower circuit in east Kent?
Richard installs shower circuits throughout the Sandwich, Deal, Dover, and Canterbury areas. Fixed price, Part P certificate included.
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