Paul Chaffers, NAPIT’s Technical Events Manager, gives advice on hot tub installations and what’s needed to comply with the Regulations to complete a safe, practical installation.
BS 7671 Requirements
BS 7671 doesn’t have any specific requirements for hot tub installations (unless it’s a commercial type of tub, like those located in a swimming pool or leisure centre), therefore, electricians will need to use engineering judgement and apply the general requirements of the Wiring Regulations when designing the installation. In some cases, comparisons can be made with BS 7671 Part 7 special installations or locations.
Where hot tubs are located inside a room, Section 701, “Locations containing a bath or shower”, could be consulted as this is the nearest parallel. For commercial hot tubs or tubs of a permanent construction built into the ground, Section 702, “Swimming pools and other basins”, should be consulted.
Within the scope of Section 702, it states that some pools are designed within the scope of an equipment standard and are outside the scope of Section 702.
Where there is any doubt, Section 702 for swimming pools could be used as a basis for a safe design. Hot tubs will either be the ‘plug-and-play’ type, fitted with a standard BS 1363 13 A plug (as illustrated in Fig 1), or will require a 32 A or 40 A supply.
Socket-outlet and/or isolator positioning
BS 7671 Fig 702.2 provides zone dimensions for basins above ground level. A representation of this can be seen in Fig 2.
Section 702 permits socket-outlets or switches to be installed in zone 2, providing the supply circuit is protected by one of the following measures:
– SELV
– Electrical separation
– Automatic disconnection of supply (ADS) with 30 mA RCD
*Note: see Regulation 702.53 for full requirements
In most cases, the most popular choice will be Automatic Disconnection of Supply (ADS) using a 30 mA RCD. Where a 13 A socket-outlet is required, it’s recommended to only install a single socket-outlet (see Fig 1). This way it will be left sealed and not disturbed, unlike a double, which may provide an opportunity for the customer to use the spare socket close to water.
In order to meet the zone requirements, the socket-outlet or isolator needs to be mounted 2 m away from the edge of the tub, as illustrated in Fig 3. Most plug-and-play tubs come with an ample amount of flex, allowing for this separation distance.
Selection of equipment for outdoor installations
Electrical equipment located in zone 2 needs to have a degree of protection of at least IPX4, and where water jets are likely, IPX5. Rotary isolators and weatherproof sockets are commonly available and typically rated at IP65.
Where a 30 A or 40 A supply is needed, and a rotary isolator is being fitted, a suitable method of final connection to the hot tub will be needed. Manufacturers may request a socket-outlet to be fitted ready for the installation team, or they may require a suitable tail to be left with the final connection being made inside the hot tub equipment enclosure.
Where a tail is required, the wiring type will need to be flexible but resilient enough to handle the external influences that it will be subjected to. Heavy-duty rubber insulated and sheathed cable H07RN-F or equivalent constructed to BS EN 50525-2-21 will be a good choice and is recognised in a number of standards as being suitable for this type of application.
The trailing cable tail should have enough length to reach the final connection position. In the absence of manufacturers’ information, a length of 5 m should suffice.
In order to be able to leave a cable tail safely, there are two options:
1. Isolate and lock off the circuit, or
2. Fit a suitable temporary junction box to the end of the cable.
Option 2 will be the recommended approach, otherwise you’ll need to return to site to energise the circuit on the day of the hot tub installation. It should be stressed that this is only a temporary measure between the electrical contractor leaving site and the hot tub installation going ahead. Every effort should be made to prevent the cable being damaged or any accidents taking place, such as trip hazards.
The temporary junction box (JB) shall be weatherproof with stuffing glands used to prevent the cable being pulled out, also preventing the ingress of water. The material of the JB should be able to take medium impact in case of any knocks. The lid of the box should be labelled with a caution that the circuit is live if switched on by the isolator.
This way every effort has been made to minimise any accidents occurring (remember, in most cases the hot tub installer will only have limited electrical skills). It may be worth a note on the Electrical Installation Certificate (EIC) that the final connection of the hot tub has been made by others.
Isolation requirements
Different earthing systems require different measures to be taken regarding isolation, however, by installing either a socket-outlet or rotary isolator, no further action is required because all live conductors can easily be switched or disconnected. By installing the switchgear adjacent to the hot tub, as illustrated in Fig 1 and Fig 3, the requirements of Regulation 132.15.201 have been met regarding an effective means of isolation.
Manufacturers’ instructions
Most manufacturers will have data sheets so that the design current can be obtained ready for the cable design. They may also specify requirements, such as type of socket or cable tail length needed, etc. BS 7671 Regulation 510.3 requires equipment to be selected and erected in accordance with the Regulations but also enforces the importance of taking manufacturers’ instructions into account.
Conclusion
Hopefully this article shows that hot tubs are nothing special and no different to any other type of equipment. It’s the presence of water that worries most, however, you wouldn’t think twice about installing an electric shower, would you?
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