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Metal conduit between two light fittings

Mark D Gray

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? 

  • 0 in reply to AJJewsbury

    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

  • 0 in reply to Chris Pearson

    Hi Chris, It is a real issue, we are installing earths to the ends of the conduits hence why it started the discussion. they area GRP linear fittings the span is approx 1m of conduit at around 3m ceiling height

  • 0

    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.

  • 0

    Is this a real issue, or just an office debate?

    What the lamp fittings are made of, even if they are double-insulated, is irrelevant. The risk arises from the cables passing through the conduit.

  • 0 in reply to aligarjon

    if the cable inside the conduit is normal singles then I'd say definitely yes too - the earthed conduit is the necessary 2nd line of defence.

    Perhaps if it was T& E or something, it would be arguably less important and just a floating conductive part.
    Or if the conduit was designed and treated like a live bus bar and in a suitable enclosure. 

    I suspect neither applies, so get those pirahna nuts at the ready ;-) 

    Mike.

  • 0

    I would say yes. If the live scags the exposed conduit it will become live if it isn't earthed.

    Gary

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