Regulation 526.9 deals with these and notes that in order to avoid separation or spreading of fine strands, ‘suitable terminals shall be used or the conductor ends shall be suitably treated’. It’s very tempting to use pliers to crimp many joints, but it is important to ensure that the correct pressure is applied uniformly, so the use of a proper ratchet crimp tool is appropriate to ensure a reliable maintenance-free joint.Īn often raised question concerns what to do with the termination of finely stranded conductors, such as in flexible cables in light fittings or plugs/sockets. An exception is also made for connections made by an ‘appropriate compression tool’, which may, for example, include crimped splices. Regulation 526.3 is perhaps better known – it’s the regulation that states that connections should be accessible for inspection, testing and maintenance, save for some exceptions, such as buried, soldered or welded joints. It is, therefore, possible to use maintenance-free joints that will not require access for inspecting or maintenance, but the joint(s) should be contained in a suitable, mechanically robust and suitably insulated enclosure – in other words, not PVC tape! When the inner cores of a cable are jointed (for example, in a terminal or spliced), the protection afforded by the sheath has been removed and needs to be replaced to provide electrical and mechanical protection. This is important for reasons of mechanical protection, as well as for electrical insulation of the connections. Secondly, the insulation around the connection should be non-flame propagating, and Regulation 526.5 requires terminations and joints to be within a suitable accessory or enclosure. Firstly, Regulation 526.4 requires that the means of connection (and its insulation) must be rated for the maximum operating temperature of the conductor, the values of which are given for different cables in the appropriate tables in Appendix 4. The thermal aspects are another consideration in selecting an appropriate terminal. Such poor joints can even cause interference if conductors are part of circuits where high frequencies are present, due to the ‘rusty bolt effect’, as well as creating noise voltages to which sensitive circuits may be susceptible. This can not only impair the effectiveness of protection of a circuit but can cause issues around the requirements for electromagnetic compatibility (Section 444), as poor joints may exhibit higher impedances at higher frequencies. Where dissimilar metals are used, galvanic corrosion can occur giving rise to high impedances. The materials used for the conductor and terminal are quite an important consideration, which is often overlooked. Where a soldered connection is used, the design shall take account of creep, mechanical stress and temperature rise under fault conditions. the provision of adequate locking arrangements in situations subject to vibration or thermal cycling. the temperature attained at the terminals in normal service such that the effectiveness of the insulation of the conductors connected to them is not impaired the number of conductors to be connected together the cross-sectional area of the conductor the number and shape of the wires forming the conductor the material of the conductor and its insulation Regulation 526.2 requires that the selection of the means of connection should take into account the following: While there is the obvious need to ensure that the connections between conductors are electrically and mechanically sound (Regulation 526.1), there are a few requirements that are often overlooked. As it happens, back then the jointing of conductors was an exercise in wrapping wires together in a rather elegant fashion, but of course, technology has moved on since and Regulation group 526 of BS 7671:2018 is where the relevant requirements are now detailed. While no competent electrician would wrap wires together and cover them with insulating tape (though it does happen!), is it actually acceptable to use any old terminal for an electrical connection?Īs befits a Standard with such a pedigree as BS 7671, there are requirements for electrical connections, just as there were in the 1st Edition, back in 1882. A common type of connector is the ‘choc block’ terminal strip, but more recently connectors using spring clamps to hold wires firmly are becoming common. Nearly every electrical installation will need to join conductors of different parts of a circuit, typically by using a connector of some type, such as a terminal block, DIN rail terminal, junction box or similar.
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