IET wiring regulations: 18TH EDITION AT A GLANCE
Lewden is committed to the safety of electrical installers and end users by being at the forefront of ensuring compliance with the new 18th edition of the IET wiring regulations BS7671:2018 that came into full effect from 1st January 2019, bringing about new guidelines and recommendations for all the professionals involved in design and maintenance of electrical installations.
A bite sized look at some of the regulation changes that relate specifically to the installation of consumer units.
IET wiring regulations - 18TH EDITION regulation explained
536.4.203 USE OF APPROVED PARTS
In low voltage assemblies to the BS EN61439 series, e.g. consumer units & distribution boards, incorporated devices and components shall only be those declared suitable according to the assembly manufacturer’s instructions or literature. Use only manufacturer approved parts, or if in doubt consult the consumer unit manufacturer to confirm compatibility. If an assembly deviates from its original manufacturer’s instructions, or includes components not included in the original verification, the person introducing the deviation becomes the original manufacturer with the corresponding obligations.
522.8.5 STRAIN RELIEF OF METER TAILS
Every cable or conductor shall be supported in such a way that it is not exposed to undue mechanical strain and so that there is no appreciable mechanical strain on the terminations of the conductors. Consumer unit meter tails are included in the requirements of this regulation.
Within consumer units, utilising the Lewden meter tails clamp accessory (MTC) satisfies this requirement.
531.3.2 CONSIDERATIONS FOR UNWANTED TRIPPING OF RCDS
New considerations shall be given to the selection of residual current devices so as to limit the risk of unwanted tripping during normal (non-fault) operation. The following shall be considered;
1. Sub division of circuits using individual RCDs/RCBOs. Devices shall be selected and circuits sub divided in such a way that any earth leakage current likely to occur during normal operation of connected load devices will not cause unwanted tripping of the device.
2. In order to avoid unwanted tripping by PE currents and/or earth leakage currents during normal (non-fault) operating conditions, the accumulation of such currents downstream of the RCD shall be not more than 30% of the rated residual operating current. Designers must take account of PE currents when sub-dividing the installation into the appropriate number of circuits.
531.3.3 TYPES OF RCD
RCCBs & RCBOs are available in various types, which are categorised depending on the ir behaviour in the presence of DC components or different frequencies. The designer of an installation must select the appropriate device type for the specific application.
