What fuse do I need for a shower pump?

Most UK shower pumps (Stuart Turner Showermate, Grundfos, Salamander RP) specify a 5 A BS 1362 fuse in a switched fused connection unit. A 3 A fuse can nuisance-trip on motor inrush, and 13 A is too large for a sub-300 W load. Always check your pump's installation instructions for the manufacturer's specified fuse rating.

Can a shower pump run off the bathroom lighting circuit?

Yes, provided the lighting circuit is already RCD-protected (30 mA), has enough spare capacity (most bathroom lighting circuits carry well under 1 A at full load, and a shower pump adds only about 1 A at 230 V), and the FCU is positioned outside Zone 0, 1, and 2 in the bathroom. A landing or airing-cupboard FCU fed from the bathroom lighting circuit is a common and perfectly acceptable arrangement.

Does wiring a shower pump need to be notified under Part P?

Adding a new circuit from the consumer unit is notifiable under Part P in England. Wiring the pump by spurring from an existing socket or lighting circuit is not notifiable, but the work must still comply with BS 7671 and be tested and certified on a Minor Works Certificate by a competent person.

Where must the FCU be positioned in a bathroom?

Outside Zone 2, which means at least 0.6 m horizontally from the edge of the bath or shower tray. The safest position is on the landing wall just outside the bathroom door, or inside an airing cupboard. The FCU must never be inside Zone 0 or Zone 1 (directly above the bath or shower base).

Can a shower pump be wired in 1.0 mm2 cable?

From the FCU to the pump terminal box, 1.0 mm2 flex or twin-and-earth is fine for the short run to a sub-300 W load. The supply spur from the socket to the FCU should be 2.5 mm2 twin-and-earth to match the ring circuit cable size and avoid a mismatch in the back box.

How to Wire a Shower Pump Electrical Supply (UK)

Helpful video reference. PlumberParts' UK plumbing tutorial "HOW TO FIT A SHOWER PUMP - Stuart Turner Showermate Review" walks through a full Showermate installation on a vented system, covering the supply pipework and the terminal box connection. Worth watching to see how the pump body sits in a typical airing cupboard and where the flex runs to the terminal.

Before you start. Isolate the circuit you plan to spur from at the consumer unit and confirm dead with an approved voltage tester at the back box. Shower pumps must not be installed in a pressurised (unvented) system -- if your hot water cylinder has a tundish and pressure relief valve on the outside, stop and consult a plumber before touching the electrical side. An unvented system runs at mains pressure; a shower pump fitted to one will damage itself and can cause a water hammer hazard.

1. Confirm the pump type and electrical rating

Before ordering accessories, read the data plate on the pump body. UK shower pumps fall into two categories: single-impeller (boosts hot or cold side only) and twin-impeller (boosts both sides simultaneously). Both types run at 230 V 50 Hz from a standard UK supply.

The rated power is typically between 100 W and 260 W depending on the bar rating. The manufacturer's fuse specification is almost always 5 A: a Stuart Turner Showermate, a Grundfos STR2, and a Salamander RP all specify 5 A. Note this figure -- you will need it when you fit the FCU.

Also check whether the pump is "positive head" (the pump outlet is below the cold tank, so gravity primes it) or "negative head" (the pump can prime even when installed above the water level). This does not change the wiring, but it matters for the plumbing connection.

2. Locate the FCU outside the bathroom zones

BS 7671 Section 701 defines three zones inside a bathroom. Zone 0 is the inside of the bath or shower tray itself. Zone 1 extends directly above the tray up to 2.25 m. Zone 2 extends 0.6 m horizontally beyond the edge of the bath or shower enclosure.

A switched fused connection unit must be outside all three zones. In most homes this means one of two places:

On the landing wall, just outside the bathroom door -- the most common choice
Inside the airing cupboard, if the cupboard opens off the landing and its wall is outside the bathroom zone boundary

Do not put the FCU inside the bathroom on the opposite wall thinking it is far enough away. Measure: if the bathroom is a tight 1.8 m wide and the bath runs the full length, Zone 2 might reach almost to the door frame.

3. Choose the supply circuit

You have two sensible options:

Spur from a bedroom or landing ring socket. Use 2.5 mm2 twin-and-earth. The FCU load is only 5 A maximum, well within the ring's capacity. Check the socket has not already been spurred before you start: pop the faceplate and count the cables.

Spur from the bathroom lighting circuit. This works if the lighting circuit already has 30 mA RCD or RCBO protection (mandatory under Amendment 3 of the 18th Edition). Run 1.5 mm2 twin-and-earth from the lighting circuit. The pump adds roughly 1.1 A to a circuit that at full load carries less than 2 A of lighting, so capacity is not an issue.

Do not wire a shower pump off an unprotected circuit or from a circuit that has no RCD coverage -- a pump in a wet environment must have 30 mA protection.

4. Fit the FCU and run the cable

Fix the FCU back box to the wall in the chosen location. Run your supply cable into the supply (line in) terminals. The FCU switch interrupts the live conductor: brown to L, blue to N, and green-and-yellow earth to the earth terminal. Fit a 5 A BS 1362 fuse in the carrier -- not 3 A (motor inrush can nuisance-trip it) and not 13 A (needlessly oversized).

Label the FCU faceplate: "Shower pump" with a printed circuit label or a marker on the inside of the faceplate. Future owners deserve to know what it isolates.

5. Wire the pump terminal box

From the load terminals of the FCU, run 0.75 mm2 or 1.0 mm2 flexible cord down to the pump. Most pumps are supplied with 0.75 mm2 three-core flex pre-fitted. If you need to extend, use the same specification and join in a suitable IP-rated junction box.

Open the pump's terminal box cover. Connect brown to L, blue to N, green-and-yellow earth to E. Tighten to the torque value in the pump installation instructions -- typically 0.5 to 0.8 Nm on a screw terminal this size. Replace the cover and hand-tighten the cover screws.

6. Test, energise and certify

With the circuit dead: check continuity of the supply and earth conductors, insulation resistance between live and earth (should be well above 1 MOhm on a new cable run), and polarity at the FCU and pump terminals.

Energise, confirm earth fault loop impedance (Zs) at the pump terminals is within the device's disconnection limit, and verify the 30 mA RCD trips in under 40 ms at five times rated trip current (150 mA). Run the pump briefly to confirm it starts cleanly with no nuisance-tripping.

Issue a Minor Works Certificate. If the spur crosses into a new circuit (for example, a dedicated radial from the consumer unit), a full Electrical Installation Certificate is required instead.

Stop and call a qualified electrician if: the pump is on an unvented pressurised system (tundish visible on the cylinder), the supply circuit has no RCD protection and you cannot add one, the airing cupboard is inside the bathroom zone boundary, or the pump wiring inside the airing cupboard shows signs of previous DIY with incorrect colours or missing earth.

When to call us

Richard installs and certifies shower pump supplies for Stuart Turner, Grundfos and Salamander pumps across Sandwich and east Kent. Whether you need a new FCU and spur or an older pump supply brought up to current regs, the job includes the Minor Works Certificate for your records.

Fitting a shower pump in Sandwich or east Kent?

Richard wires and certifies the electrical supply so your plumber can get water flowing the same day. Part P registered, fully insured.

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How to wire a shower pump electrical supply