A dedicated wall chaser is your friend, here, as you can set the disc depth to the minimum you need and no more, and know it will be stuck to. Hire one with a dust extractor and you're good to go. Use it also to run the lines for your boxes for the same reason and go easy on the hammer afterwards - lots of little light taps will do far better than a big whack which takes the block out!
You might also like to have a bag of readymix mortar or bonding coat to hand - just in case it all goes wrong!
You might also like to have a bag of readymix mortar or bonding coat to hand - just in case it all goes wrong!
It's basically impossible to run a cable unsupported in a cavity wall to current regulations.
I don't think that's what the OP is asking. He's asking about hollow blocks - that's the ones that look like an '8' if you stand them up.
Agh my bad. Ignore my comment then. And make sure you don't knock out to much.
My guess is he already has - else why would he know??! :detective:
uksparks
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If you can get into the cavity you could drop pipes in like I did on a rewire, see pic below. Was a very neat job actually, the pipes only went up two feet in the cavity though, was a fiddle getting them in as they were 50mm.
As cables cannot just be put into the cavity without some form of protection from debris, falling objects, poly insulation etc, pipes was the best way, just popped up my local fish shop and it didnt cost much, ok it was a fiddle getting it in, but its done now and so easy to rod more cables through.
As cables cannot just be put into the cavity without some form of protection from debris, falling objects, poly insulation etc, pipes was the best way, just popped up my local fish shop and it didnt cost much, ok it was a fiddle getting it in, but its done now and so easy to rod more cables through.
uksparks
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Master craftsman... I don't feel that good yet, but I know I always do a good job, it probably took me an hour to get 5 pipes in, the cavity was only 60mm I think and the pipe was 50mm, that's why I had to knock a few bricks out to get it in as there were a couple of ties in the way! But yes, this was a job I was pleased with.
Looks like those compression glands are for supply tails , and db looks metal clad wot I'm getting at is metal ( ferrous ) enclosure just wondering if you have slotted knockouts or have tackled that in anyway? . Must say like the job very tidy will be making a mental note of you tekkers there .
I have understood that its a no no with wiring in cavity's unless mechanical protection blah di blah and don't really get why ( just becouse cable is not supported ?? ) my best guess . But I guess that cables in a 9 meter vertical galv trunking is supporting cables???
Just came into my head maybe cavity wiring may bring on the occurrence of damp issues ?? Just a though
Just came into my head maybe cavity wiring may bring on the occurrence of damp issues ?? Just a though
uksparks
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Yes both boards are metal, the one at the top, the compression glands, I drilled these in ready to put the supply cables in as you pointed out and the little black one was to put the earth in. There are knockouts on the bottom board, I used them for trunking to the garage stuff etc and fire alarm switch.
Where I carefully cut out the top board to take the cables in the back instead of through the top in a header thing, I have superglued a rubber edge (got loads of it from eBay for next to nothing) on as per the photo below to ensure no damage can be done to the cables over the cut edge. I didn't do that on the bottom as the edge was very smooth and rounded over so didn't feel it needed it to be honest.
I am sure you can see I take care in my work and try to think of the what if's and buts.
Where I carefully cut out the top board to take the cables in the back instead of through the top in a header thing, I have superglued a rubber edge (got loads of it from eBay for next to nothing) on as per the photo below to ensure no damage can be done to the cables over the cut edge. I didn't do that on the bottom as the edge was very smooth and rounded over so didn't feel it needed it to be honest.
I am sure you can see I take care in my work and try to think of the what if's and buts.
I'm was purely commenting on those stuffing glands as all live and neutral conductors should enter a ferrous enclosure via the same hole as to prevent eddy currents on you're earthed metal/ferrous enclosure ( db ) but a way around that is to cut a slot between each hole so I'm tolled , yes I agree you do a tidy job and obviously have pride in wot you do good job
uksparks
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I agree about the eddy currents, but to be honest, its only drawing 90A I think on the three phase board, about 30A per phase, it's not something I'm going to loose sleep over, yeah if it was significantly more then I would have put them in the same hole. The 24 hour board, they did enter through the hole on the right in one, it was only the top one that was like it. I appreciate eddy currents are obviously not made up, but at what current would you expect to experience them, or anything noticeable?
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I'm going now else Ill be late...
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I'm going now else Ill be late...
When I first read the original post, I assumed it was a 2 skin cavity wall he was referring to, ie. two breeze-block leaves. You're probably right though with the hollow blocks, it's just that I've never heard of them referred to as 'cavity blocks'. Daz
I don't think there are exceptions to the regs just best we abide regardless if we think!( as u or I don't know exactly!! the risk is with eddy's ) the risk is minimal , things to take into account is maybe wot if the installation purpose changes and that board starts using more than 90a ?? The installation obviously requires more than the usual property as it was deem'd to req three phase and least two additional db's , I'm not trying to drag into a debate was just a pointer , issues concerning eddy current's I can only guess so I won't as il probably get leathered on this site!
Hi.
Just to clarify, I mean cavity blocks, e.g. http://www.dme.co.za/sites/site1/images/Brick_Simulation/rockface_block_M6.jpg.
The house is a 70s build.
I have put in some of the chases but when I went to put it a box I broke through to the hollow of the box.
I fixed wood inside the block as something to mount on, this worked fine but I'm worried about compromising the structural integrity of the walls by chasing them like this.
Just to clarify, I mean cavity blocks, e.g. http://www.dme.co.za/sites/site1/images/Brick_Simulation/rockface_block_M6.jpg.
The house is a 70s build.
I have put in some of the chases but when I went to put it a box I broke through to the hollow of the box.
I fixed wood inside the block as something to mount on, this worked fine but I'm worried about compromising the structural integrity of the walls by chasing them like this.
uksparks
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I take both your points on board and will learn from it. I'll be honest doing mainly domestic and light commercial I don't tend to touch much three phase etc. You are quite right it could be picked up later on. Incidentally I have got a little extra work to do at this property at some point in the next couple of weeks so will probably cut a few slots as it will not take long and I know I will have done what I can then.
Scania164, I don't think for one minute I would be chasing these walls as they are not cut out for it, I feel you would be dramatically compromising the integrity of the blocks if you chase them.
Scania164, I don't think for one minute I would be chasing these walls as they are not cut out for it, I feel you would be dramatically compromising the integrity of the blocks if you chase them.
What have they been covered in? Screed then plaster??
Are you sure?
This poster doesn't seem to share your opinion.
Yeah, just over 10mm of plaster on top of it.
Cap it down wall no chase then chase and bed socket in using bonding / board adhesive whatever make Mr plaster work for his bunce . I've had this before mr plaster sayd he was giving a skim ! I come back 2 weeks later and I need to invent a 3ft extension screw as he's gone and dot and dab'd !
uksparks
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Post 25, I agree with what you are saying and I know you are allowed a third, but you would knowingly cutting into a surface that's what is it? An inch thick? With a hollow void, he can do as he likes, but I feel it would not be the best thing to do, but that's my opinion, I know what the regs say, but surely there's an element of it cannot apply to every type of wall and common sense is required. If you cut a third into one of those blocks you will end up in the cavity.
Agreed. Which is why you don't need to. #27
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