Chasing cavity block wall

[scania164]

I need to run new wiring down a cavity block wall.
It is possible for me to chase it but it doesn't seem like a good idea.

What options are available to me?
I loathe surface mount and will do pretty much anything to avoid if.

-Thanks

 

[telectrix]

chase it. you are allowed 1/3 of the thickness of the block vertically, and 1/6 of the thickness horizontally. is the wall plastered? if so, that's enough for your cables. cut deeper for socket boxes, but be wary if it's hollow block.

 

[Rockingit]

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!

 

[ChrisElectrical88]

It's basically impossible to run a cable unsupported in a cavity wall to current regulations.

 

[Rockingit]

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.

 

[ChrisElectrical88]

Agh my bad. Ignore my comment then. And make sure you don't knock out to much.

 

[Rockingit]

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:

 

[DPG]

I don't think he's mentioned hollow blocks - only a cavity wall. Could still be solid blocks. Daz

 

[uksparks]

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.

 

[Badged01]

Whats this piddly thingy label I see at the bottom for ......



I reckon that would have been a b*tch of a job to get those pipes in but the end result does you full credit for a real professional finish! Get your label changed to "master craftsman working"!

 

[uksparks]

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.

 

[Rockingit]

I need to run new wiring down a cavity block wall.

I don't think he's mentioned hollow blocks - only a cavity wall. Could still be solid blocks. Daz

Eh????

 

[Aindowsimon]

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.

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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 .

 

[uksparks]

Does he mean a cavity in a double block wall? If its a solid brick wall he's stuffed anyway! Right I'm off to the dentist now to have a root canal!

 

[Aindowsimon]

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

 

[uksparks]

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.

 

[Aindowsimon]

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]

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?

- - - Updated - - -

I'm going now else Ill be late...

 

[DPG]

Eh????

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

 

[Aindowsimon]

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!