Passing cables through cavity wall

[Danny]

Chaps .. this is my first post .. I have my DI assessment coming up soon and

have a job lined up to install external lighting ..

Cables need to pass through the cavity wall to the outside and i'm sure I saw it described somewhere but now can't find it ...

Am i right in saying put it through 20mm PVC conduit and then fill it with flame retardant foam .. ? Doc B etc ...

And would a snug hole for the conduit sealed with silicone satisfy it also ..

Thanks in advance ..

 

[green-hornet]

Hello and welcome to the forum Danny.

Cables passing through a cavity should be selected for use or protected against external influences, in a cavity to an outside wall this may be things like falling debri etc.

A neat hole with conduit run through would do.

There is no need to seal with fire foam unless the cable has to pass through a fire barrier.

So sealed with silicone would be ok.

 

[Danny]

Excellent ... thanks ...

 

[Doc Hudson]

Welcome to the forum Danny.

Doc H.

 

[a1]

Welcome to the forum Danny.

 

[Apache]

Hello and welcome Danny boy

where in the world are you from?

Tell us about yourself!

 

[a1]

PS - Officially (Non-real world) Isn't the passing of cables through a "Cavity" a no-no?

 

[ianmacd]

NO that's running the the cavity because you can't ensure you will not allow moisture to traverse the cavity (Reg C).

Ian.

 

[a1]

NO that's running the the cavity because you can't ensure you will not allow moisture to traverse the cavity (Reg C).Ian.

Yes, and someone could drill through it, could get scagged on the Wall ties and the house could have cavity wall insullation at a later date etc?

 

[Danny]

Thanks chaps but now i'm a little confused .. The cable has to get out somehow and all the external walls are cavity .. also 2W switches both inside and out will be another run through the cavity ..

Thanks again for the welcome .. I'm in Lewes, East Sussex and setting up as a very local DI ..

As i said in my ealier post i'm sure i saw a diagram of how it should be done but for the life of me i can't find it so i'm here for the definitive

Stuff goes through cavities all the time .. waste pipes, etc so is there a difference for conduit?

 

[green-hornet]

No you will be ok running a conduit through the cavity, I always drill at an angle very slight it stops any moisture comming through directly or by capillary action.

You will have complied with all the regulations about protecting the cable from any damage and will not effect the installation of insulation in the future.

 

[ianmacd]

Yes, and someone could drill through it, could get scagged on the Wall ties and the house could have cavity wall insullation at a later date etc?

If the cable is only going from one skin to the next though the cavity, how will it "get snagged" on a wall tie or someone else drill though it? Are you confusing going across the cavity with running the cable inside the cavity?

Running in conduit (with a slight downward angle from inside to out so stop moisture coming back in) and sealing with silicon/cement/etc.. is the best way as then it is protected from things falling inside the cavity (snots for example) and from direct contact with any cavity wall insulation that could degrade the insulation of the cable.

Ian.

 

[ianmacd]

Jinx GH.

Welcome to the asylum too, Danny.

Ian.

 

[Apache]

Yes, and someone could drill through it, could get scagged on the Wall ties and the house could have cavity wall insullation at a later date etc?

Admin - that thing in your signature will get annoying!

 

[a1]

Admin - that thing in your signature will get annoying!

If it has drawn your attention to it - it is working.

 

[Danny]

Great ... thanks guys .. back to plan A then ... conduit, slight angle .. cemented at either end to stop moisture getting back in ..

Roll on assessment ... (did i really just say that?!?)

 

[Theorysparky]

i have a question regarding this post....

to get a 20mm piece of conduit through 2 walls u will needf a hole of 22mm +

if drilling at a slight angle how do you prevent 'blowing' of the outside brick ?

and if you are going through a cavity with new cable it must stand to reason that all older cables in the house do at some point.

Surely these older cables would suffer the same fate quicker with debri and insulation.

 

[a1]

If the cable is only going from one skin to the next though the cavity, how will it "get snagged" on a wall tie or someone else drill though it? Are you confusing going across the cavity with running the cable down the cavity?

yes I was Ian - Sorry. Blushing

 

[Theorysparky]

as the red book is not law ,,,not sure i would bother with conduit

if you blew a brick badly what you going do ????

replace it ?????

what if there is rendering and that crumbles ?????

all jobs assessed on its merits ........

 

[green-hornet]

as the red book is not law ,,,not sure i would bother with conduit if you blew a brick badly what you going do ????

replace it ?????

what if there is rendering and that crumbles ?????

all jobs assessed on its merits ........

One way I find that works to stop the outside brick from blowing is to send a 10mm drill through first then drill each cavity from the outside skin, finally drill from one side to make sure the drilled hole is debri free and in line.

If the outside wall is rendered this can be very tricky as the render will as you have said or implied come off in a big chunk if not done with care.

The practice of sending the cable through conduit is to provide additional protection, and ease of maintenance and replacement.

Its not law just good practice and a neater job in the end.

I often use conduit through a cavity wall to place external lighting, and its great the conduit is terminated with a suitable seal in the fitting with no cable on show and looks like a pro neat job.