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Leakage from underfloor steel conduit trench

K Samoei

I recently inspected an old building whose wiring is drawn in underfloor steel conduits in a trench openable from the floors above (1st and 2nd floor)., and branching of to lighting and power points.  Despite the rust as shown here, the installation is in ‘working condition’.  However, there are two concerns. 

First, water ingress from cleaning is staining the soffit/ceiling under and it's a nuisance to users. Second, the old wiring used the steel conduit system as a CPC and rust could have reduced it's effectiveness.

I have thought of covering/encasing the trench permanently but two issues arise. How to deal with draw-off points at corners and at 10m interval; and the possibility that rewiring may be rendered impossible in the future.

I would appreciate any comment from anyone who has had to reckon with this such a challenge and how they approached it.

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    Hello

    Tests over time will show any deterioration of CPC function especially if the results are graphed.  Is there space to draw in a separate CPC if required.  If its close to the limit you might want to replace or supplement anyway.

    One option you could consider would be to fill the trench with an expanding foam.  If you chose this carefully it will be waterproof and soft enough to be removable if you need access to the conduits.  If you go this way make a carefully dimensioned drawing showing inspection covers, joints etc relative to permanent building structures or dimension same on a photograph.  Also tape up / over any screws that you might want to remove.

    If you do fill with foam do it a metre at a time and place a plastic sheet and heavy board over the top to confine the foam.  You will need quite a lot of weight to keep it in and level with the top of the trench.  The foam wont normally stick to polythene so that can then be peeled off carefully.

    Hope this helps.

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  • 0

    Hello

    Tests over time will show any deterioration of CPC function especially if the results are graphed.  Is there space to draw in a separate CPC if required.  If its close to the limit you might want to replace or supplement anyway.

    One option you could consider would be to fill the trench with an expanding foam.  If you chose this carefully it will be waterproof and soft enough to be removable if you need access to the conduits.  If you go this way make a carefully dimensioned drawing showing inspection covers, joints etc relative to permanent building structures or dimension same on a photograph.  Also tape up / over any screws that you might want to remove.

    If you do fill with foam do it a metre at a time and place a plastic sheet and heavy board over the top to confine the foam.  You will need quite a lot of weight to keep it in and level with the top of the trench.  The foam wont normally stick to polythene so that can then be peeled off carefully.

    Hope this helps.

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