Went to see a pair of new build semis today to find out when I can get in to fit the kitchens and I saw something I have not seen before. The cable routing holes through some of the joists where visible, (much has already been boarded) have been drilled and sleeved, the sleeves look to be plastic or painted steel and protrude approx 25mm either side of the joist.The only people on site were the boarders so I could not ask the sparks themselves.Out of interest only do any of you experts know if this is a requirement of the 17th regs or maybe a new building reg as I have not seen this before.I could perhaps understand it if the outer diameter of the holes were less than 50mm from top or bottom of the joists and the sleeves were steel to give mechanical protection but these were deep joists and the holes looked about on centre. Many thanks Wes.
Sleeving cable route holes through joists
- Thread starter wesj
- Start date
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Sounds odd TBH.
No requirements to do so.
Shame you could not have taken a pic or two.
No requirements to do so.
Shame you could not have taken a pic or two.
If I can be *rsed to do it, and *rsed to take them, I might one day post photos of my cables running on cable tray between joists, supported on mini joist hangers.
Not required, but neat.
Just a thought, wesj, how far from the top of the joists were the holes for cables? <50mm by any chance?
Not required, but neat.
Just a thought, wesj, how far from the top of the joists were the holes for cables? <50mm by any chance?
I do hope you have cross bonded all the trays together BAS, and taken an earth back to the MET . I look forward to seeing some pics one day
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Thanks for your replies guys, and B,A.S. way over 50mm from top or bottom, joists were about 200-250mm deep and holes about on centre. Perhaps just a personal querk of the sparks,I hear some even use cable tray to span joists to stop sagging. I could understand if the cable route was through supporting walls, settlement and all that. If I see the sparks when I fit I will find out and let you know
were the joists oak?
Oak sap is acidic and can eat thru insualtion.
Maybe this was being addressed
Oak sap is acidic and can eat thru insualtion.
Maybe this was being addressed
No ebee,I think I only work for cheapskates,bog standard pine
you lot not read the latest fire regulations then?
it's to stop thermal damage to the joists should the cables overheat..
the 25mm each side is so that the tube can dissipate the heat.. acts kind of like a heat sink....
oh and btw, everything above was totally made up.. I have no idea either..
having said that though, they might be intumescent sleeves for sealing the wiring penetration if the area will be a fire stop area? ( ie a flat in a block? or above a kitchen or garage etc? )
it's to stop thermal damage to the joists should the cables overheat..
the 25mm each side is so that the tube can dissipate the heat.. acts kind of like a heat sink....
oh and btw, everything above was totally made up.. I have no idea either..
having said that though, they might be intumescent sleeves for sealing the wiring penetration if the area will be a fire stop area? ( ie a flat in a block? or above a kitchen or garage etc? )
I do hope you're joking (unsure with the lack of a smiley!)
Well I suppose it's just believable that it's for strength - drill hole remove meat make it weaker, bush hole with stronger material and good adhesive and you retain some strength.
Bit far fetched though
Bit far fetched though
Holes in the centre line of a joist do not significantly reduce the joist's strength. ( Assuming the load is bending the joist downwards then the top layers are under compression along the joist and the bottom is being stretched, the meat in the middle has very little stress in it. )
Green oak and freshly vacuum treated timbers ( anti fungal etc ) do secrete chemicals which have an effect on PVC so lining them is a good idea. When we put gas pipes through freshly treated timbers ( Tanalised )the use of sleeving or bitumen coating was suggested for this reason.
"Holes in the centre line of a joist do not significantly reduce the joist's strength. ( Assuming the load is bending the joist downwards then the top layers are under compression along the joist and the bottom is being stretched, the meat in the middle has very little stress in it. )"
Correct Bernard,
it's a lifetime ago I did sheer force and bending moments.
Any removal of meat does cause a reduction in strength and this can be minimised by positioning (on the nuetral axis so far as bending moments are concerned) and by making corners rounded rather than sharp edges such as in a radii or a circle. The reduction is devised to not be too significant by following the rules we have in place for holes and notches.
Correct Bernard,
it's a lifetime ago I did sheer force and bending moments.
Any removal of meat does cause a reduction in strength and this can be minimised by positioning (on the nuetral axis so far as bending moments are concerned) and by making corners rounded rather than sharp edges such as in a radii or a circle. The reduction is devised to not be too significant by following the rules we have in place for holes and notches.
Hi
I am just interested to know if you have found out if they are plastic or metal yet?
Martin
Oh and this does sound like a good idea to me. not sure I am ready to hang cable trays between joists tho. BAS which ones do you use, ie where from send us a link if you can be *rst.
I am just interested to know if you have found out if they are plastic or metal yet?
Martin
Oh and this does sound like a good idea to me. not sure I am ready to hang cable trays between joists tho. BAS which ones do you use, ie where from send us a link if you can be *rst.
maybe to prevent screws going thru cables
No - I have given each length its own earth rod, connected via 16mm² tri-rated cable.
Is this not OK?
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