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FAQs

Below you can find a number of Frequently Asked Questions that are regularly posed to our technical helpline.

General Technical FAQs

Can a PME supply be used to supply a swimming pool?

BS7671 currently sets out no specific requirements on the type of earthing systems to be used in swimming pool installations. 
It does however require that where a metallic grid is provided in a solid floor, and can be considered as an extraneous conductive part then supplementary bonding is provided to connect the grid to other extraneous conductive parts and the protective conductors of all exposed conductive parts in the zones.

Can equipment such as washing machines be installed in a room containing a bath or a shower?

Washing machines, etc, are classed as electrical equipment and are allowed provided they have a rating of at least IPX4 if sited in Zone 2. Any standard wiring accessory however used to connect the appliance must be outside of Zone 2, or if not be also suitably IP rated - and in all cases protected by a 30mA RCD. Socket Outlets are not allowed closer than 3m from the edge of Zone 1.

Can I certify other contractors' work if I am a member of a Competent Persons' scheme?

Approved Part P covering electrical safety in dwellings applying in England since April 2013 now defines two types of sign off.

‘Self Certification’ and ‘Third Party Certification’.

Self Certification as its name suggests allows only work undertaken by a registered self certifying contractor to be notified via a Part P scheme.

If a scheme operator offers a ‘Third Party’ Certification membership category and a contractor is registered as such then work carried out by others can be notified via this route.

The majority of Self Certification Schemes however only operate Self certification membership categories.

You can, however, provide a Periodic Inspection Report or complete the testing section of an Electrical Installation Certificate provided that you have inspected the work during the construction phase.

Can I install a spur off an existing circuit without being registered on a Competent Person scheme?

You can install a new spur from an existing circuit without being registered on a Competent Persons' scheme provided it is not in a special location. Note that the different versions of Approved Part P, applying since April 2013 defined special locations and what is notifiable work differently in England and Wales.

Do caravans come under the scope of Part P?

No; providing it is a proper caravan, i.e. it meets the requirements for the construction and use of road vehicles, it does not come under the scope of Part P regardless of whether it actually moves or not.

Does the connection of equipment, i.e. cookers/boilers, etc. require notification under Part P?

No; connection of equipment to an existing point is not notifiable work even in a special location or a kitchen.

Do I need to install fire hoods/fire rated downlighters in every situation?

It really depends on whether the ceiling forms part of a fire compartment, its type of construction, its load-bearing capacity or if it has been specified by the client/contract.

Generally speaking, many dwellings are considered to be a single compartment with regards to fire (Part B of the Building Regulations) unless it has an integral garage or has a protected stairway leading to a third floor.

In the case of 3-storey dwellings, it is advisable to fit fire protection to downlighters installed in intermediate floors, especially where the integrity of flooring above has been compromised (e.g. gaps between floor boards, etc.). 

Where recessed downlighters are installed in ceilings that are not fire compartments such as the intermediate floors of 2-storey dwellings, the ceiling usually needs to have a minimum fire rating of 30 minutes. 

In all cases, it should be remembered that when working with any existing aspect of the building regulations applying in existing situations, the general requirement is to be seen as making any particular aspect no less compliant than before the work was carried out.

Do I need to install main bonding if it is missing or undersized if I am installing a new circuit?

If you are installing a new circuit and you are relying on automatic disconnection in the event of an earth fault, it follows that you are relying on there being an equipotential zone. To ensure there is an equipotential zone, main bonding to incoming services must be carried out.

If the main incoming services, etc, are bonded but the conductor is undersized in relation to the current BS 7671 Regulations, you should bring it to the customer's attention and upgrade it if requested. Reg 132.16 requires earthing and bonding to be adequate before any alteration is undertaken.

Do I need to provide RCD protection on a shower circuit?

Under the 17th Edition, all circuits in a bath/shower room require 30mA RCD protection.

Do I need to provide supplementary bonding in a commercial kitchen?

Supplementary bonding of metal work surfaces, etc, is not a specific requirement of BS 7671. The designer of the electrical installation may, however, perceive there to be an increased shock risk in that particular location and specify additional bonding.

How close to sink/basin can a socket outlet be located?

BS 7671 does not specify any minimum distance for socket-outlets to be from a sink. However, regulation 512.2.1 requires external influences to be considered when selecting equipment for a particular location. Accessories used in domestic installations are not designed to be splashed and therefore not suitable for installation close to a sink or draining board. For this reason, industry-accepted guidance and good practice is that socket-outlets and other accessories should be located at least 300 mm, measured horizontally, from a sink or draining board, where they are less likely to get splashed.

When asked to carry out an installation in a metal-framed building divided into several separate units, i.e. multiple occupancy, I find that the electricity company will not provide a means of earthing. Why is this?

It should be remembered that an electricity distribution company has no obligation to provide an earthing facility, although most cases one is provided.

New LV supplies are often TNC-S. If multiple supplies are taken into a metal-framed building occasionally the earthing and bonding arrangements can lead to circulating currents around the building structure, which in turn can cause electrical interference (EMI) in user equipment within the building as well as safety issues.

Where an earthing system cannot be provided by a distribution company for any reason, one option may be to provide a TT system.

When using a 3-core cable in the new harmonised colours on a single-phase installation, which core can I use for the CPC and which for the Neutral?

Under BS7671, when any cable is over-sleeved or marked (with the exception of single-core green/yellow which must not be over-sleeved or marked), the over-sleeving or marking takes precedence over any colour underneath and therefore any combination can be used. However, a convention has been generally accepted of over-sleeving or marking the black with green/yellow (CPC) and the grey with blue (Neutral). This has been done with the aim of helping to disassociate the colour Black with Neutral.

Where pipework in a bathroom is plastic, do I need to supplementary bond the bath/radiator, etc?

No; if the pipework is substantially plastic with only short metal stubs connecting the taps/radiators, etc. these can be treated and if need be tested and proven to be  isolated pieces of metalwork and do not need to be bonded.

On metal pipework installations, under the 17th Edition, provided all the circuits of the location are protected by a 30mA RCD and there is continuity between the extraneous conductive parts and the protective (main) equipotential bonding, then supplementary bonding is not required.