Richard Townsend, Technical Development Engineer at NAPIT, takes a detailed look at BS 7671: 2018, Section 702 on swimming pools and other basins.
So, why are swimming pools classed as a special location?
Despite what many would see as an obvious risk potential, swimming pools, or any similar basin, are seen as a special location for one main reason, namely the ability of the human body to conduct electricity more efficiently when it is wet. So, when we’re wet, our resistance to current flow is reduced, by our emergence in water, the risk of coming into contact with an Earth potential is increased and the likelihood of receiving a fatal shock if we did so, is also. It is now clear why swimming pools and other basins have specific electrical installation requirements.
It’s all about the Zones
Section 702 has Zones allocated to various areas of a swimming pool or basin. Each Zone has a higher level of safety required, which carries with it restrictions as to the supply voltage and equipment allowed. Zones for a swimming pool are:
● Zone 0
● Zone 1
● Zone 2
These Zones are better understood by the example pool layout seen in Fig 1. 
Zone 0
Zone 0 is the most onerous of the Zones and will generally contain the water element of a swimming pool along with its encapsulating walls. It includes water jets or any other similar features that may form part of a swimming pool.
Zone 1
Zone 1 generally consists of the area directly associated with the use of the pool. It is indicated by the following distances:
● 2.0 m from the basin section of the pool (any paddling area is considered to be a basin)
● 2.5 m above the basin or any other part of the pool or its associated fixtures
The term ‘fixtures’ refer to:
● Chutes
● Diving boards or platforms
● Anything expected to be used or occupied by persons
Zone 2
Zone 2 is less onerous than Zones 0 and 1. It is generally an area 1.5 m from the edge of Zone 1, up to a height of 2 m.
What’s in a Zone?
The Zones have different risks associated with them. We can now see which equipment and wiring systems can be used in each of them.
Zone 0
If the pool is in use, only Separated Extra Low Voltage (SELV) supplies with a voltage not exceeding 12 V AC RMS or 30 V ripple-free DC should be used. The source for this type of supply must be located outside of Zones 0, 1 and 2. When the pool is not in use, other supplies may be used for specialist cleaning equipment, such as:
(i) SELV – with the source installed outside Zones 0, 1 and 2, unless the circuit is protected by an RCD to Regulation 415.1.1, it can be located in Zone 2
(ii) ADS – using an RCD in accordance with 415.1.1
(iii) Electrical Separation – in accordance with Section 413, supplying only one item of equipment is installed outside Zones 0, 1 and 2, unless the circuit is protected by an RCD to Regulation 415.1.1, located in Zone 2.
Points (i) and (ii) allow for more traditional power supplies; however, any socket-outlets or their controls for these purposes must be clearly labelled. Regulation 702.512.2 states equipment must be IPX8 rated and specifically designed for use in a swimming pool, in accordance with Regulation 702.55.1. Switchgear, control gear and junction boxes, or socket-outlets of any nature cannot be installed in Zone 0. Only wiring systems for equipment intended for Zone 0 should be located in Zone 0. All extraneous-conductive-parts must be connected by supplementary bonding to the protective conductors of equipment with exposed-conductive-parts situated in all three Zones, as called for by Regulation 702.415.2. So, when considering your electrical designs, Zone 0 has very restrictive requirements.
Zone 1
It is essentially the same as Zone 0, with the following ‘relaxations’: Zone 1 equipment must be a minimum of IPX4 rated, or IPX5 if water jets are likely for cleaning, as stated in Regulation 702.512.2. Also, it should be specifically designed for use in a swimming pool, in accordance with Regulation 702.55.1. Junction boxes for SELV circuits and only wiring systems for equipment to be used in can be installed in Zone 1.
Zone 2
The restrictions are as Zones 0 and 1 with the following exceptions: In Zone 2, all equipment must meet IPX2 rating for indoor pools and IPX4 rating for outdoor pools, or IPX5 rating where water jets will likely be used for cleaning, as stated in Regulation 702.512.2. There are no restrictions for it being specifically designed for Zone 2; however, it would be wise to use pool specifically designed equipment where it is available. Voltage sources restrictions remain the same as the other two Zones. Switchgear, control gear and junction boxes, or socket-outlets can be installed in Zone 2, provided they’re supplied by one of the methods allowed for the other two Zones.
Is that it?
Section 702 is one of the larger sections of Part 7 and includes other areas to consider, which were more than this article could cover. Fountains are also covered in Section 702, but there’s no Zone 2 in a fountain, and there are some other restrictions on equipment types for them, specifically the mechanical protection of luminaires and a specific standard for pumps (BS EN 60335-2-41). Also, remember where designers put pools in areas where either heights or perimeter distances cannot achieve the minimum Zones. There are caveats regarding luminaires, their supplies, and where they can be mounted in these cases. Likewise, where there is no Zone 2 of a pool (by design), socket-outlets and switches may be placed in Zone 1 with a minimum distance of 1.25 m from Zone 0 and with a minimum height restriction of 0.3 m above the floor.
Free-standing structures are generally an addition to existing installations, where a sunken basin is not possible or where a pool may be above ground level. Although the Zones are the same, they may take on individual nuances due to quirky designs that need careful consideration. Fig. 2 gives an example of free-standing pool zones. Swimming pools notoriously carry a high maintenance price tag, both in equipment and labour costs. Given the corrosive nature of the chemicals and products used in their upkeep, the presence of these products in the air, and humidity associated with pool rooms, requires equipment maintenance to be both regular and stringent. When carrying out an EICR, extra thought needs to be given to the sample rate of accessories that have or could have been exposed to these corrosive effects. Complete dissolution of copper conductors and components in socket-outlets and other accessories due to corrosion is common, even in equipment designed to be IP rated for wet areas. Any maintenance and/or replacement of lifecycle expired equipment needs to be carefully chosen and installed to ensure safety during use and maximum service life.
Recommendations
Given the very specific requirements for swimming pools, the best advice is to tackle designing or carrying out an EICR on them if you are competent and have experience. If anything is missed or not adequately catered for, the potential for harm is high, and swimming pools should be dealt with cautiously. A Risk Assessment should always be carried out prior to any work on or around a swimming pool. Advice on risk assessments can be found in NAPIT’s Risk Assessment and Management Code of Practice, which is available as an electronic book.
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