Running lighting cable over/through joists in loft.

May 15, 2006 3 Replies
T

The joists in my loft are less than 100mm in height, meaning that it is impossible to drill a hole that is 50mm from both the top /and/ bottom of the joist. I've found other posts that say to run the cable over the top of the joist and have a baton either side and place steel strips over the top, e.g.

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parts the cable/joists will have boards over the top. Can the cable be run without earthed trunking/conduit? and does this comply with the building regs? I can't find anything which explicity covers this in the On Site Guide or the BS7671 Blue Book.



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L

Why not drill through the joists 50mm from the bottom and put 3mm steel plates over the top to protect from screws.

I beleive this is allowed in the on site guide

Regards - Lightingman

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T

As a slight aside, given the height of the joists will I be able to run the cables along the length/side of the joists, holding them in place with cable clips?

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J

This is acceptable, and is the standard way of installing Twin & Earth, PVCI cables running the length of the joists. If there is thermal insulation laid "between the joists", the cable should be run preferably, at a height corresponding to the upper surface of the insulation layer, to avoid unnecessary cable derating; but in any case, at a height of at least 50mm to the underside of the cable, measured from the bottom of the joist. (This is to avoid possible nail damage from below the ceiling).

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