What is an acceptable method of running a ring main through floor joists? Can I bore just one hole through each joist and run both cables for the ring through that? Or one smaller hole for each cable. The cable will run the length of the hallway to the kitchen so there's probably about 10 joists to bore through. Also I want to install Earth bonding from kitchen to CU. Can I run the 10 mm green/yellow through the same set of joist holes as one of the 2.5 T+E? All help appreciated. Steve.
Routing 32A ring main through floor joists
- Thread starter steve1811uk
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Yes you can.
Building regs do give spec's for hole size and position. My copy is out on loan, so I can't quote the details (exactly).
From memory the hole must be no bigger than 25% of the joist size, so 4" joist = max 1" hole. If more than one hole needed they must be spaced no less than 3 x diameters away from each other
There's also distance rules about where on the joist the holes should be placed for new work.
If the joist has redundant holes, they can be used without consideration of the building reg requirements (such would apply on a re-wire, where you might use the same route as existing cable)
Can the cable (if running on the g/f) not be loose run under the joists and sat on the sub floor foundation?
Building regs do give spec's for hole size and position. My copy is out on loan, so I can't quote the details (exactly).
From memory the hole must be no bigger than 25% of the joist size, so 4" joist = max 1" hole. If more than one hole needed they must be spaced no less than 3 x diameters away from each other
There's also distance rules about where on the joist the holes should be placed for new work.
If the joist has redundant holes, they can be used without consideration of the building reg requirements (such would apply on a re-wire, where you might use the same route as existing cable)
Can the cable (if running on the g/f) not be loose run under the joists and sat on the sub floor foundation?
You can do either as long as the hole diameter isn't larger than 1/4 of the joist depth and are made in the centre of the joist. If you drill multiple holes ensure they are 3 diameters apart. Also make sure you are drilling in the area 20% and 40% from the joist ends.
You can run the bonding cables in the same holes but they'd have to be pretty big holes, so better to drill separate ones for the bonding conductors.
Davy
You can run the bonding cables in the same holes but they'd have to be pretty big holes, so better to drill separate ones for the bonding conductors.
Davy
Thanks for the help. I planned to run them through the joists down the hallway to the kitchen. I can just about reach 20% as the hallway is 44 inch wide and the total joist length is 200 inches. But the hallway narrows to 36 inch and then I cannot reach 20% (only 18% from the wall). Am I missing something here? surely I don't have to pull up the dining room floor as well ! Steve.
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Sorry, I gave those figures from memory and it seems my memory is failing, it's actually 25% - 40% of the beam span, so it looks like the dining room is going to have to come up anyway.
Another option is to notch the joists, this has to be done within 7% - 25% of the span but the cable will need mechanical protection. The notch can not be more than 1/8th of the joist depth.
Davy
Another option is to notch the joists, this has to be done within 7% - 25% of the span but the cable will need mechanical protection. The notch can not be more than 1/8th of the joist depth.
Davy
Chri5 said:
Good point Chri5. I should be able to clip it on the underside of the joists. I can't see that being a problem regarding safety...Other opinions on this approach are appreciated.
That's fine too, make sure they are clipped under every single joist and try to prevent any droops where rodents might be able to nibble away at them.
Davy
Davy
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Saw an 85mm diameter hole cut in a joist 3" thick & 11" deep today......
Interesting! Also, it was VERY close to the wall.
Wish I had got a picture of it, but mobile battery was too low.....
Interesting! Also, it was VERY close to the wall.
Wish I had got a picture of it, but mobile battery was too low.....
Please see forum rule 27G part g section 14b:
All DIYnot members must carry a fully functioning camera at all times.
All DIYnot members must carry a fully functioning camera at all times.
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