Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning BS7671: 2008, and whether an earthing tail is required from back boxes to earth any accessory incorporating an earth terminal, is answered by SELECT:
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| A back box - but an earthing tail needed? |
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Question: I was under the assumption that if metal back boxes had fixed securing lugs, then a trailing earth lead from the socket to back box was not required. Is this correct?
Answer: For wiring systems where the CPC is provided only by metal conduit, trunking or a metallic sheath of a cable, an earthing tail is required from the back box to earth any accessory incorporating an earth terminal, such as a socket outlet or a metallic light switch.
Where the wiring system incorporates a separate conductor to provide the CPC (e.g. FT&E cables), the requirement to provide an earthing tail depends upon the type of accessory and the type of fixing lugs in the back box.
Where an accessory does not have an earth terminal, such as a plastic light switch, the CPC must be terminated at the earth terminal on the back box.
For accessories incorporating an earth terminal, where the box has two fixed lugs it can considered to be earthed via the accessory eyelets and an earthing tail to the back box is not essential.
Where the box has one fixed lug, provided the accessory has an earthed eyelet on the fixed lug side, again an earthing tail is not essential.
Where the box has two adjustable lugs an earthing tail to the back box is essential.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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Related contacts
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SELECT
The Walled Garden, Bush Estate,
Midlothian, Scotland EH26 0SB
Tel: 0131 445 5577
Fax: 0131 445 5548
Email: admin@select.org.uk
Web: www.select.org.uk |
SELECT
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Source: SELECT & James Hunt |
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