Cables in cavity - wall being built

[loply]

Hi folks,

Just about to start putting up a cavity wall breezeblock garage and I've got a run of 6 sockets on each wall.

Don't want any conduit on the walls if possible and don't want to chase in so many cables.

I'm hoping to build conduit (or just raw cable?) in to the cavity as the wall goes up, but the sparky seems reluctant.

Was thinking of putting a series of bits of conduit into the mortar with elbows so I can pull the cable through later... or should I just get them to stop at the right height one day and cable clip the cable to the inside of the cavity?

Anybody know a good solution?

Cheers,
Rich

 

[Taylortwocities]

You cannot put cables in wall cavities. They can bridge the cavity and cause you grief later.

Also guidance from the Electricity Safety Council says "installing such cables in this way (external cavity walls) is generally an undesirable practice"

The reasons give are
1. Obstructions in a cavity wall, such create a risk of unseen damage during installation.
2. Long unsupported vertical drops may place undue strain on the conductors, leading to damage
3. Polystyrene used for insulation, if it come into contact with thermoplastic (pvc) cable sheathing, plasticiser can migrate from the thermoplastic to the polystyrene
4. Thermal insulation in the cavity may cause cable not to be able to carry the load current without overheating due to their current-carrying capacity being reduced
5. Presence of flora and fauna - unforeseen external influences

There is also a requirement in the Building Regulations 2000, Approved Document C, 2004 Edition, Section 5: Walls, paragraph 5.13 b
and NHBC Standards state that no cables other than electricity meter tails are to be located in the cavity of an external wall.

 

[ban-all-sheds]

Don't want any conduit on the walls if possible

It's a garage. How much time do you expect to spend in there admiring the purity of walls unsullied by conduit?

and don't want to chase in so many cables.

That will be 1 cable. Not a lot really. And a chasing tool will work a treat on lightweight blocks.

I'm hoping to build conduit (or just raw cable?) in to the cavity as the wall goes up, but the sparky seems reluctant.

You have an electrician - use him to do the installation of the cables, then after the walls have been made good by the plasterer and painted by the decorator, you can go in there and soak up their beauty.

 

[loply]

1. Obstructions in a cavity wall, such create a risk of unseen damage during installation.
2. Long unsupported vertical drops may place undue strain on the conductors, leading to damage
3. Polystyrene used for insulation, if it come into contact with thermoplastic (pvc) cable sheathing, plasticiser can migrate from the thermoplastic to the polystyrene
4. Thermal insulation in the cavity may cause cable not to be able to carry the load current without overheating due to their current-carrying capacity being reduced
5. Presence of flora and fauna - unforeseen external influences

I'm talking about affixing conduit horizontally, from socket-to-socket, inside the cavity as it's being built, which avoids all of the things you've mentioned.

 

[JohnW2]

I'm talking about affixing conduit horizontally, from socket-to-socket, inside the cavity as it's being built, which avoids all of the things you've mentioned.

If I understand your proposal correctly, there would be (inaccessible) right-angled corners/elbows at the end of each run of conduit (behind sockets) - and it would not necessarily be easy pulling cables through that.

Kind Regards, John

 

[RF Lighting]

What ever way you try and dress it up, it's always going to be cack. Do it properly and do it the normal way like everyone else does.

 

[loply]

Nobody has yet proposed an actual reason not to do this. Silly and completely baseless references to bridging cavities and protecting cables are just knee-jerk and thoughtless.

There are 18 sockets in total, wall mount conduit will be in the way, and vulnerable to heavy machines, welding sparks, all sort of stuff.

Saying cables will be inaccessible when enclosed in conduit in the cavity, then suggesting chasing the wall and cementing them in? For god sake... Logic anyone?

Sometimes I think electricians are a bit too much slaves to their own silly rule books and have no ability to think.

 

[RF Lighting]

Just do what ever you like no one cares.

We've told you it's not allowed. It's not what you wanted to here so you start calling us.

Watch the door on your way out.

 

[loply]

What I'm asking is whether or not there's a reason...

Flora and forna, polystyrene beads, etc, all irrelevant in this instance as I've stated the cables will be in conduit securely fixed to the inner leaf and protected.

Impossible to accidentally screw into when putting a shelf up, protected from welding sparks and general machinery, etc etc.

If there is no reason, and there's just a rule which doesn't apply to this particular case, I will disregard it, because I'm not a total and utter imbecile.

 

[JohnW2]

Saying cables will be inaccessible when enclosed in conduit in the cavity, then suggesting chasing the wall and cementing them in? For god sake... Logic anyone?

Unless I need another trip to Specsavers, I don't think anyone has said anything about the cables being 'inaccessible' - as you say, that's equally the case when they are chased in.

I did mention that the elbows would inaccessible, but that was only in the context of presenting a possible practical problem for you in pulling cables through - nothing to do with the inaccessibility of the cable, rules or regulations.

Kind Regards, John

 

[flameport]

Saying cables will be inaccessible when enclosed in conduit in the cavity, then suggesting chasing the wall and cementing them in? For god sake... Logic anyone?

There is a huge difference between cables concealed under plaster and those inside a cavity wall.
Plaster can easily be removed and replaced. Entire walls cannot.

If you want to use conduit inside the cavity horizontally between sockets, then the lengths between sockets will need to have bends formed on each end, and the ends threaded and connected into the back of each box using the appropriate bush or other connector.
Preformed elbows and other fittings cannot be used, as it will be impossible to draw wiring in afterwards.
The conduit will need to be fixed to the back of the inner wall, requiring that the inner wall is constructed before the outer one.
To accommodate the bends in the conduit, the back of the wall will need to be dressed appropriately and the resulting spaces filled with mortar or other suitable material after the conduit is installed.

All of this will take a huge amount of time and cost a fortune.
The description above applies to steel conduit only. There is no satisfactory way to do it using plastic.

 

[sparkwright]

Isn't there a rule somewhere cables are ok in the cavity if they are clipped (to the inner wall I suppose)?

 

[loply]

It would be pretty silly if it's okay for a cable to be clipped to one side of a wall (the sides humans are present using tools, saws, screwing things, etc), but not the other side!

The cables can quite easily be pulled through conduit with two elbows, as I've done it before. A little fairy liquid helps. And the right conduit.

If the wire ever needs replaced (why on earth would it?) it could just be yanked out and a new piece of string vacuumed through and the wire replaced... A lot easier than smashing off mortar etc.

The inner wall can be built the same time as the outer, when it reaches the right height one extra course on the inner is all that's required and the conduit can be screwed in place ready to go. The cables could even be fed in at this stage I suppose.

 

[sparkwright]

Ok.

 

[EFLImpudence]

Just do what ever you like no one cares.

We've told you it's not allowed. It's not what you wanted to here so you start calling us.

Watch the door on your way out.