Chase out or Cavity

[Clarkster]

I am carrying out a rewire and it will form my assessment piece for a scheme membership. I have a query regarding whether to chase out a wall in order to get the cables up to the first and second floors, or place inside the cavity as it was previously wired. A 17th edition board is going to be fitted so presumably chasing will be ok the cable will be less than 50mm from the surface but will be RCD protected. Advantage of cavity less mess.

Next question,

When distributing circuits, 1st floor lights ground floor sockets on one side Ground floor lights and 1st floor sockets on the other. What would you guys reccomend regarding adding the second floor to this arrangement. I would like to just add in to first floor sockets and lighting as the cable is pretty much up there as against bringing cable all the way from downstairs. Would this be ok its part of an assessment piece don't forget.

Any suggestions welcome.

 

[steptoe]

some people have differing views on this,

my opinion is that a cavity is not considered suitable for running cables through, and would not comply with the regs.

 

[springcrocus]

I agree with Albert. You have no control over what happens in the cavity, nor can you adequately support your cables in this space.

If, in a couple of years time, the owners decide to have the cavity filled with insulation then your cables may well end up under-rated.

Also, it would be difficult to prevent your cables touching BOTH walls at various points, and this means that moisture now has a route across the cavity.

 

[Sharpend]

Make an assessment of the existing circuits and judge whether they will take the extra floor on the proposed circuit. If this assessing is good and safe to proceed take the feeds from first to second floor. I hold probably look to chase through a socket location on he second floor and run up to it then on into the loft space for both lights and sockets, but them I haven't seen the layout.

Cavity in my opinion is a no-no as per steps.

 

[Clarkster]

Many thanks that's really helped there are only two rooms up there so only three lights including the landing and 4 sockets max.So I'll add to the on first floor circuits and label appropriately.Thanks again

 

[safedepth]

I agree with Albert. You have no control over what happens in the cavity, nor can you adequately support your cables in this space.If, in a couple of years time, the owners decide to have the cavity filled with insulation then your cables may well end up under-rated.

Also, it would be difficult to prevent your cables touching BOTH walls at various points, and this means that moisture now has a route across the cavity.

Does that mean that all wall ties installed during construction should be replaced? Of course not.

How much more likely is moisture going to track across a cable than all those ties?

Your other reasons I agree with but bridging is frankly silly.

 

[Steve3948]

I agree with Albert. You have no control over what happens in the cavity, nor can you adequately support your cables in this space.If, in a couple of years time, the owners decide to have the cavity filled with insulation then your cables may well end up under-rated.

Also, it would be difficult to prevent your cables touching BOTH walls at various points, and this means that moisture now has a route across the cavity.

So the outside lights or outside sockets don't touch both then.

Before cavity wall insulation was invented a lot of installations were wired in the cavity, and I have never seen any damaged when we have ripped it out, however I agree in this day and age it would not be good practice.

 

[Badger]

couldnt you take the wiring through an airing cupboard from lower ceiling to loft

 

[batty]

You are doing a rewire and need to get the cables up to the next floor. Its just a little bit more chasing. I generally will take it up a light chase or sockets up another socket chase. Also you need to get a smoke detector cable up so a bit of chasing is going to be needed. Cables down cavities is a no no these days just ask any scheme provider.

 

[revjames]

the only credible reason for not using a cavity is the possibility of the cable becoming surrounded by thermal insulation.

 

[batty]

And possibly getting damaged on wall ties when pulling it through.

 

[springcrocus]

I disagree with those who say that water traveling across can be disregarded.

Wall ties (and insulation) are at a constant temperature within the cavity or have a very small temperature gradient across them. Therefore, condensation is unlikely to form on these items. Cables, however, have fluctuating temperatures depending on load and this can allow condensation to form on the cable.

I agree it's not a big deal in the scheme of things, but it is the reason why, if cables must cross the cavity, they should include a drip loop.

 

[batty]

Or drill up at an angle slightly that way any water will run back.

 

[Steve3948]

I disagree with those who say that water traveling across can be disregarded.Wall ties (and insulation) are at a constant temperature within the cavity or have a very small temperature gradient across them. Therefore, condensation is unlikely to form on these items. Cables, however, have fluctuating temperatures depending on load and this can allow condensation to form on the cable.

I agree it's not a big deal in the scheme of things, but it is the reason why, if cables must cross the cavity, they should include a drip loop.

And how exactly do you check your drip loop.

I know that's the sh*t they tell you at college but in practice well.

 

[springcrocus]

And how exactly do you check your drip loop. I know that's the sh*t they tell you at college but in practice well.

Simple, I don't shove cable willy-nilly across the cavity. I always install some 20mm plastic conduit across the gap and stick my cable in that. The air-space around the cable helps limit the temperature variation of the conduit.

Maybe you should ask your local BCO what he thinks of you just shoving cable through the wall?

And since the electrician who taught me a heck of a lot some forty years ago taught me this, it's good to see that colleges today still teach the same old sh*t.

 

[Steve3948]

Simple, I don't shove cable willy-nilly across the cavity. I always install some 20mm plastic conduit across the gap and stick my cable in that. The air-space around the cable helps limit the temperature variation of the conduit. What temperature variation that's over the top it's minimal over that distance, however well done you for installing conduit.Maybe you should ask your local BCO what he thinks of you just shoving cable through the wall? You kidding me, I would ask them nothing, and would expect them to say "well its no different to having an outside tap, waste pipe, overflow pipe or even soil pipe".

And since the electrician who taught me a heck of a lot some forty years ago taught me this, it's good to see that colleges today still teach the same old sh*t. I doubt they still teach this today, although that's how it should be done, in practice well you decide

You did say drip loop, which they did teach at college, but like I said how do you check your drip loop, to much and and it would touch the wall and be worse than not having one, as said above drilling at an angle stops any remote chance of tracking.

 

[batty]

Trouble is what you learn at college doesn't happen in the real world. We were taught to strip cable with a Stanley knife, yes they allowed them then. But get real how can you use a Stanley knife when cables are tight at the top of a box not very practical at all and possibly dangerous to. Stripping with the cpc to my mind is a lot safer and then snipping with wire cutters.

 

[Steve3948]

I must say I have never been a lover of stripping cable using cpc, always looks messy.

I was taught to use a blunt knife with the blade angled towards cpc, I use a blunt Snickers Workwear knife.

However as an apprentice I remember cutting my finger where the blade went under my nail, where copper was back from the end of pvc so knife shot off at an angle.

 

[PC Electrics]

I have actually seen film taken from the inside of a cavity whilst the outside was being sprayed to simulate rain. The bricks become soaked after a while and water starts to run down the inside surface of the outer brick leaf.

Take a look at the picture of the wall tie:

Wall Tie 225mm For 76-100mm Cavity Pack of 25 | Screwfix.com

you will see it has some bends in it in the middle. This is to provide a low point from which water can drip rather than tracking across the cavity.

My detached garage has single leaf brick walls. Thanks to the garage position and local prevailing wind conditions one wall becomes soaked by driven rain. I used to get puddles of water on te garage floor after rain. When I painted the inside of the garage white I got big brown stains in the paint. I ended up waterproofing the outside of the wall with Thompsons Brick Sealer.

Water transmission through bricks is not a trivial issue.