You’re so very special

Part 7 of BS 7671:2008 makes specific references to electrical installations in areas defined as ‘special installations or locations’. As well as having to comply with the general requirements of BS 7671 (parts 1 to 6), some further requirements or restrictions apply to installations in special locations.

New special locations for Part 7 are:

• Bathrooms
• Swimming pools
• Agricultural and horticultural
• Caravan parks
• Exhibitions, shows and stands
• Photovoltaic (PV) cells
• Mobile or transportable units
• Floor and ceiling heating units.

The regulations specify that designers and installers must assess the environment, use and risks at the locations for which they are designing and constructing, and make provisions accordingly. A high level of competence and relevant experience is required.

Locations with a bath or shower

See 'Bathrooms get a clean up' (linked below)

Swimming pools and other basins

BS 7671: 2008 retains the next special location in Part 7 as ‘Swimming pools and other basins’. The ‘other basins’ addendum is important as this applies to basins of fountains and to areas incorporating natural waters, including sea and lakes, where they are specifically designated as ‘swimming areas’.

Swimming pools and basins pose similar risks to bathrooms, in that people are generally unclothed and body contact resistance is low. Some fountain basins are likely, or even expected, to be occupied, and as such they should be treated as swimming pools, as far as BS 7671 is concerned. Often, a risk assessment will need to be carried out to assess whether fountains need to be treated as fountains or swimming pools.

Electric shock requirements are these:

• All extraneous conductive parts in all zones – except fountains – must be supplementary bonded.
• For separated or safety extra-low voltage (SELV) and protected extra-low voltage (PELV), basic protection must be used.
• Only SELV up to 12 V ac or 30 V dc can be used as a protective measure in zone 0 in swimming pools.
• Only SELV up to 25 V ac or 60 V dc can be used as a protective measure in zone 1 in swimming pools.
• Protective measures in zone 2 in swimming pools can be SELV, residual-current device (RCD) automatic disconnection or 'single-item' electrical separation.
• Protective measure in zones 0 and 1 in fountains can be SELV, RCD automatic disconnection or'single-item' electrical separation.

Equipment selection and erection requirements are:

• Equipment in zone 0 shall be to IP X8.
• Equipment in zone 1 shall be IP X4.
• Equipment exposed to cleaning jets should be to at least IP X5.
• Surface metallic wiring sheaths or conduits, or those less than 50 mm deep, must be connected to the local supplementary bonding.
• In zones 0 and 1, no switchgear is permitted.
• In zones 0 and 1, no socket outlet is permitted.
• In zones 0 and 1, only equipment designed for a swimming pool can be used.
• In zones 0 and 1 of swimming pools, a floor heating unit is allowed if it is SELV, RCD-protected and covered with earthed metal grid.
• Luminaires shall comply with BS EN 60598-2-18.
• In swimming pools, zone 1 pool equipment (pumps etc) shall be in a class II enclosure, only accessible with a tool, and have 25 V ac SELV (60 V dc) or electrical separation.
• For swimming pools without a zone 2, luminaires can be installed in zone 1 and do not need to be 12V SELV, but must be RCD-protected and at least 2 m above the floor.

Agricultural & horticultural premises

Section 7 of the revised BS 7671: 2008 looks at fixed electrical installations inside and outside agricultural and horticultural buildings, including locations where animals are kept.

It does not apply to residences or other locations such as shops, workshops or storage areas.

An increased risk of damage to the electrical installation and an increased risk of personal danger can come from a number of factors, including:

• the use, possibly widespread, of chemical cleaners and fertilisers
• behaviour and nature of animals (stock and vermin)
• agricultural machinery
• frequent wet and damp conditions
• lower body resistance of livestock.

The requirements for agricultural and horticultural installations are:

• Final socket-outlet circuits with socket outlets up to 32 A require a 30 mA RCD.
• Final socket-outlet circuits with socket outlets above 32 A require a 100 mA RCD.
• All other circuits require an RCD not exceeding 300 mA.
• For SELV and PELV, basic protection must be used.
• Where livestock is kept, supplementary bonding shall connect exposed and extraneous conductive parts; this includes floor reinforcing.
• Copper conductors must be 4 mm2 minimum; steel bonding must be galvanised and a minimum of 8 mm in diameter or 30 x 3 mm by section.
• Where the welfare of animals is affected by loss of supply – food or ventilation – a standby supply shall be installed, and separate final circuits shall be used. Alternatively for ventilation systems, monitoring and alarms can be used.
• Ventilation supply circuits shall be designed to achieve discrimination.
• Electrical heaters for livestock shall be to BS EN 60335-2-71.
• All equipment must be to IP44 as a minimum.
• Obstacles and equipment placed ‘out of reach’ are not permitted.
• Non-conducting locations and earth-free equipotential bonding are not allowed. 

Caravan parks and camping parks

Section 708 covering caravan parks (including camping parks) does not apply to mobile homes. ‘Caravan parks/camping parks’ are defined as an area of land that contains two or more caravan pitches and/or tents.

However, a caravan is defined as ‘a trailer leisure accommodation vehicle, used for touring, designed to meet the requirements for the construction and use of road vehicles’.

The requirements of BS 7671 for caravans and camping parks are:

• TN-C-S arrangements are not permitted.
• Equipment must be a minimum of IP44.
• Overhead cables must be a minimum of 6 m above where vehicles are used, and 3.5 m elsewhere.
• The supply point at the pitch must be a maximum of 20 m from the caravan inlet.
• Pitch socket outlets must be provided with at least one outlet, at a minimum of 16 A, to IP44, a BS EN 60529 type and located between 0.5 m and 1.5 m high.
• Each pitch socket outlet must be provided with over-current protection and 30 mA RCD.
• Obstacles and ‘out-of-reach’ are not permitted.
• A non-conducting location or earth-free local equipotential bonding are not allowed.

Exhibitions, shows and stands

Section 711 of the special locations requirements applies to temporary exhibitions, shows and stands.

Most exhibition and show organisers will require an electrical installation certificate for each stand’s electrical set-up before they allow connection to the local supply.

Generally, electrical systems should be as simple and robust as possible. Modular installations systems with plug and socket outlet connections have been developed to go with prefabricated modular stands.

Requirements are as follows:

• A cable supplying a temporary exhibition, show or stand shall be additionally protected with a 300 mA RCD and shall discriminate with final circuits.
• Obstacles and ‘out-of-reach’ are not permitted.
• A non-conducting location or earth-free local equipotential bonding are not allowed.
• Structural metal on stands, caravans, wagons or containers must be main-bonded.
• Socket-outlet circuits up to 32 A and lighting circuits must have 30 mA RCD, but emergency lighting is excluded.
• Where SELV and PELV are used, basic protection must be provided.
• Cables shall be at least 1.5 mm2.
• Butyl flex must not be used when there is no fire alarm.
• Joints in cables shall only be made for connecting into circuits.
• A joint system must be to at least IPX4.
• Separate units require isolators.
• All motors must have isolators located adjacent to them.
• An adequate number of socket outlets must be provided.
• A visible switch must be provided for signs, lamps and exhibit circuits.
• An installation must be inspected and tested after each assembly.

Photovoltaic cells

For safety reasons, BS 7671 includes a section on solar photovoltaic (PV) power supply systems.

In this section, terms used to describe the subject are PV cells (individual cells), PV strings (a circuit arrangement of PV cells), PV arrays (a general term for a collection of cells, possibly comprising a number of PV strings), and PV system (the cells or arrays – sources of sustainable energy – their control and connection).

PV system requirements are:

• PV ac supply must be connected to the supple side of a protective device.
• A type B RCD to IEC 60775. An RCD is not required where the PV construction is not able to feed the dc fault.
• Class II is preferred on the cell's dc side.
• Overload protection may be omitted from the PV array string if the cable current-carrying capacity is rated to at least 1.25 times the short-circuit current. Protection for the latter current must be provided at the mains connection.
• When maintenance work needs to carried out on the dc and ac sides, isolation must to be provided.
• All junction boxes must carry a label warning about energisation after loss of mains power.
• Protective bonding conductors must run in close contact with dc and ac PV cables.

Mobile or transportable units

This is new to the 17th Edition and is perhaps the most unusual section of the special locations as it covers a range of units from specialist broadcast vehicles to simple skid-mounted units.

This section has been included because questions concerning connection to the units or their inspection are frequently put to electrical contractors, although units are designed by manufacturers.

Some of these requirements can only be undertaken at the manufacturing stage:

• Automatic disconnection must be through an RCD.
• Socket outlets must be 30 mA-protected, unless they are SELV, PELV or by electrical separation.
• Accessible metal parts like the chassis must be main-bonded, using finely stranded conductors.
• TN-C-S (protective multiple earthing, PME) shall not be used.
• Unit supply cables must be flexible to BS 919 or equivalent, a minimum diameter of 2.5 mm2 and must enter the unit via an insulating sleeve or enclosure.
• Unit supply connectors must be to BS EN 60309-2 and insulated to IP44.
• Electrical equipment must not be run in a gas storage area, except for gas-supply control.
• Every unit must have an electrical rating plate, indicating the earthing set-up, voltage phases and maximum power.
• Obstacles, ‘out-of-reach’ are not allowed.
• A non-conducting location or earth-free local equipotential bonding are not allowed.
• Alternatively, an IT supply can be used, with insulation monitoring, with an RCD to disconnect if the isolating transformer fails.

Floor and ceiling heating systems

This section is new to BS 7671:2008.

Electric floor and ceiling heating systems are mainly used in domestic and similar installations and are usually buried in the building fabric at a shallow depth.

The main risks of such systems are overheating and physical damage after installation as the systems are not visible.

The requirements are:

• Automatic disconnection must be by a 30 mA RCD.
• Heating units (cables, tape or panels) that are not manufactured with a conductive covering or mesh must be protected by a metal mesh or grid with spacing of not more than 30 mm.
• A maximum operating temperature of 80°C must be achieved through design, installation or sensing. Floor areas should be colder – say 35°C – for skin comfort.
• Heating cables must be to BS 6351 and flexible sheet panels must be to BS EN 60335-2-96.
• Heating units – cables or panels – for floor installation must be to IPX7.
• Information must be given to the user of the installation.