Wiring an electric shower

Wiring an electric shower

Wiring an electric shower.

Before making any electrical connections within the installation, make sure that no terminal is live. If in doubt, SWITCH OFF the whole installation at the consumer unit or switch fuse (where fitted).

The appliance must be earthed by connecting the supply-cable earth conductor to the earth terminal.

Radial circuit
A separate, permanently connected supply must be taken from the consumer unit to the appliance through a double-pole switch, which has at least 3 mm of contact separation. The switch can be a ceiling mounted pullcord type within the shower room, or a wall mounted switch in an adjacent room.The switch must
must have a mechanical indicator showing when the contacts are open. An indicator lamp alone is not sufficient. It MUST NOT be connected to a ring main, spur, socket outlet, or lighting circuit.

How to wire an electric shower
Supplementary bonding
Within the bathroom or shower room, all accessible conductive parts of electrical equipment and extraneous conductive parts (metal parts) that are likely to introduce earth potential, must be electrically bonded to earth using a minimum cable size of 4.0 mm² if the cable is not mechanically protected, (2.5 mm² if mechanically protected). These parts include metal baths, radiators, water pipes (including the feed to the shower), taps and waste fittings.

Choosing cable and fuse sizes
The minimum cable size (cross-sectional area) required should be in accordance with BS 7671. Read the manual first, before select the cable size. The current rating of your cable must be at least that of the shower itself. The maximum lenght of a circuit is limited by the permitted voltage drop and the time it takes to operate the fuse or MCB in the event of an earth fault.

Shower power rating
up to 9.2kW from 9.2 to 11.4kW
cable size [mm2] 10 10
size of earth wire [mm2] 4 4
current rating of fuse circuit [A] 45 -
current rating of MCB [A] 40 50
max. cable lenght using fuse [m] 31 -
max. cable lenght using MCB [m] 52 25

Do not  use rewirable fuses.

RCD protection
Electric shower has to have a separate radial circuit, which must be protected by 30mA RCD.

See also:


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