[ Technical: FAQs ]
achieved in the required time, supplementary equipotential bonding shall be provided. In this instance, if disconnection will
not occur in the required 0.4 seconds, for example, supplementary equipotential bonding is used to hold various exposed conductive parts and extraneous-conductive-parts at substantially the same potential to limit the risk of an electric shock. To generalise, supplementary equipotential
bonding is used where a disconnection time cannot be met, or where a ‘special installation or location’ – i.e., those in Part 7 of BS7671:2008 – gives an increased risk of electric shock.
Q|Do I need to install main bonding if installing a new circuit?
it is missing or undersized, if I am
A|If you are installing a new circuit and you are relying on automatic
disconnection in the event of a 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 are bonded but the conductor is under sized to the current BS7671 regulations, you should bring this to the customer’s attention and recommend an upgrade.
Q|Can equipment such as washing machines be installed in a bathroom?
A|Washing machines are classed as transportable equipment and are
allowed outside of Zone 2 provided they are protected by a 30mA RCD and permanently connected, or connected to a socket outlet sited more than three metres horizontally from the boundary of Zone 1.
Q|Do caravans come under the scope of Part P?
A|No – providing it is a proper caravan and 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.
Q|When using a three-core cable in harmonized colours on a single-phase
installation, which core can I use for the CPC and which for the neutral?
A|Technically, 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-sleeve 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). The thinking behind this has been done with the aim of helping disassociate the colour black with neutral, and the shade of grey being a neutral colour.
A|It really depends on whether the ceiling forms part of a fi re
Q|Do I need to install fi re hoods/fi re- rated downlighters in every situation?
compartment, its construction, and if it has been specifi ed by the client or contract. Generally speaking, a dwelling is considered to be a single compartment with regards to fi re (Part B of the Building Regulations) unless it has an integral garage or has a fl oor that is above 4.5m from the ground (three- storey). In the case of three-storey dwellings, fi re
protection should be fi tted to down-lighters between the upper two fl oors, unless the fi rst and second fl oors are served by a protected stairway leading to two fi re separated routes on the ground fl oor, or directly to an exit door (no fi re-separating fl oors in this situation). Where recessed down-lighters are installed in ceilings that are not fi re compartments,
such as the intermediate fl oor or a two-storey dwelling, the ceiling needs to have a fi re rating of 30 minutes. Research was commissioned in 1996
to look into the effect on the fi re resistance of plasterboard ceilings with conventional rectangular joists having recessed down- lighters installed with no boxing or fi re hoods. The results, which were published in the July 1996 edition of Building Control magazine, confi rmed that downlighters, even without being boxed in and with no fi re hoods in plasterboard ceilings, have little signifi cant effect on fi re resistance ratings up to 30 minutes. It must be inferred from these tests that, at least with plasterboard ceilings with conventional rectangular joists, it is not necessary to box in down-lighters or to use fi re hoods for the purpose of restoring the fi re resistance capability of ceilings that are not a fi re compartment.
Any questions?
If you have any questions you’d like answered by ECA Technical Services, or if you require any further information on issues raised here, please contact Will Lloyd or Giuliano Digilio at the ECA Technical Services department. Call 020 7313 4850, or email
will.lloyd@eca.co.uk or
giuliano.digilio@eca.co.uk
July 2011 ECA Today 65
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