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Passing cables through joists

I know that this has been discussed in the old forum, but I have been pondering the subject over the past couple of days.

I am more than happy to respect the exclusion zones at the ends and in the middle of joists (Electrician's Guide to the Building Regulations); but it seems odd that cables which are passed through joists must go through notches in the zone between 0.07 - 0.25 times the span, and holes in the 0.25 - 0.40 zone.

In essence, despite the removal of a substantial amount of material, the upper joist in my diagram is acceptable, but the 16 mm hole in the lower one is not.

6023a2338ff6952232f44f2cc4478e57-huge-20190802joist.jpg

It seems to me that any risk to the cable is much lower in holes than notches; and of course, if plumbers have already occupied the notch zone, there isn't much choice.

In order to remove and replace cablies descending to sockets below, I need to lift the second board in from the wall; but it would be a real PITA to have to lift another board (especially if tongue and groove) closer to the centre of the room particularly because there isn't much working space unless the furniture is removed.

I have no intention of placing holes below notches, but will the house fall down if I don't follow the Guide? ?

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0 ebee over 5 years ago

You could calculate both sheer stress and bending moments about joists etc, I last did this at college and never used the maths in real life though. The regs give us the rules about holes and notches as an easy fix to stay well within the need for the calcs. So for a simple life goodho says I.

It`s not too difficult to lift T & G floorboards, easipeasi methinks chipboard, especially if nailed not screwd down is another matter though.Moving furniture is all part of the job but if you can avoid it then good.

You do see places where somebody has put a hole near a notch or vice versa though. Case in point my avatar is just such a thing. I carefully cut and removed said chipboard and drilled holes in correct places then threaded cables. I had to break off to allow a "Warm Front" team to do their bit. Guess what? the used the same parts of the span and put joists over/near the holes (they also soldered their pipework without using a solder mat and splattered solder all ove the cables too. Ruffnecks.

PS those notches they butchered in were massive compared to what was needed. They just did not give a 4X about it!
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0 ebee over 5 years ago

You could calculate both sheer stress and bending moments about joists etc, I last did this at college and never used the maths in real life though. The regs give us the rules about holes and notches as an easy fix to stay well within the need for the calcs. So for a simple life goodho says I.

It`s not too difficult to lift T & G floorboards, easipeasi methinks chipboard, especially if nailed not screwd down is another matter though.Moving furniture is all part of the job but if you can avoid it then good.

You do see places where somebody has put a hole near a notch or vice versa though. Case in point my avatar is just such a thing. I carefully cut and removed said chipboard and drilled holes in correct places then threaded cables. I had to break off to allow a "Warm Front" team to do their bit. Guess what? the used the same parts of the span and put joists over/near the holes (they also soldered their pipework without using a solder mat and splattered solder all ove the cables too. Ruffnecks.

PS those notches they butchered in were massive compared to what was needed. They just did not give a 4X about it!
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Passing cables through joists

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