Hi all,
we are having a discussion in the office and wanted your thoughts on the subject. If you have a metal conduit fitted between two plastic light fittings, the circuit is wired in singles (including a separate CPC), is there a requirement to earth the metal conduit?
Only exceptions I can think of if is the circuit isn't normal LV - e.g. SELV or perhaps separated LV, or (very rarely) if the conduit was out of reach (unlikely in uncontrolled environments like normal offices).
- Andy.
If I have visualised the situation correctly, the metal conduit would appear fall within the definition (BS 7671 Part 2) of an exposed-conductive-part:
'Conductive part of equipment which can be touched and is not normally live, but which can become live under fault conditons'
As an exposed-conductive-part, connection to a protective conductor would be required by 411.3.1.1.
If not connected to a protective conductor, you would only have basic protection (provided by the insulation of the conductors within the metal conduit) but you would not have any fault protection in the event of failure of the insulation, the classic 'single fault to danger'.
Some exemptions to the provision of fault protection are listed in 410.3.9 (i) to (v) but none would appear to apply in the situation described.
- Ross
Something tripped a memory about this over the weekend, and following a trip to the archive and going back as far as BS 7671 : 2001 (Amendments 1 & 2) the equivalent regulation to 410.3.9 was 471-13-04.
471-13-04 permitted protective measures against indirect contact to be dispensed with in instances numbered (i) to (vii) one of which was:
'(v) inaccessible lengths of metal conduit not exceeding 150 mm'
If the conduit in the original question has a length ≤ 150 mm and is inaccessible, then it might have complied at one time.
However, the requirement of inaccessibility would be difficult to meet in most situations, as even if the conduit is inaccessible in the normal use of the installation, it is likely to become accessible at some point, for example during maintenance work.
- Ross
Something tripped a memory about this over the weekend, and following a trip to the archive and going back as far as BS 7671 : 2001 (Amendments 1 & 2) the equivalent regulation to 410.3.9 was 471-13-04.
471-13-04 permitted protective measures against indirect contact to be dispensed with in instances numbered (i) to (vii) one of which was:
'(v) inaccessible lengths of metal conduit not exceeding 150 mm'
If the conduit in the original question has a length ≤ 150 mm and is inaccessible, then it might have complied at one time.
However, the requirement of inaccessibility would be difficult to meet in most situations, as even if the conduit is inaccessible in the normal use of the installation, it is likely to become accessible at some point, for example during maintenance work.
- Ross
Ross, very impressed with your memory! :-)
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