Hooking up lamppost to circuit for external wall lamp

[ToolbeltDandy]

When my mum's house was renovated, the wiring was replaced and lamp was added to the exterior of the kitchen wall, with a switch on the inside of the same wall.

I've installed a lamp-post at the bottom of the garden and would like it to be controlled via the same switch.

If the wall-mounted lamp was installed in accordance with regulations, will it be on a separate circuit from the rest of the kitchen?

I would like to connect my lamp-post via the same switch.

In the following picture, you can see part of our house (left) and the neighbouring house (right). It is part of a row of terraced houses that I guess are about 80 years old. Does this mean that there are two layers of brick with a space in between, where the electrics used to go? Will the electrics now be in conduits on the inner surface of the walls, instead?

I'm trying to get a feel for what I need to do so I can be as efficient as possible (I hope to do it when I return home for Christmas).

Incidentally, what is the black area, under the rendered area called? Is that for stopping water ingress?

 

[Lectrician]

Cables will be flushed into the wall and plastered over.

Going by the red bricks on the right hand house, this is a solid wall, not a cavity. You can tell by the rows of bricks showing their short sides.

Cables should not be run in a cavity anyway.

There is no reason why the outside light on the wall should be on a different circuit to the kitchen lighting.

I assume you are going to run SWA cable, at a suitable depth, and gland it both ends accordingly?

 

[PrenticeBoyofDerry]

To determine whether the outside light is part of the kitchen circuit would need to turn that part of the circuit off and see if the light is then isolated.
If it is there is a good chance that it will be, but it could be a circuit all of it's own or feed from another circuit within the house.
Running cables within the cavity is a no no, so the cable fro this switch should be buried within the internal leaf of the property, if the cable is not surface mounted. It will at some point go vertically through both internal and external leafs.
But for your lamppost to be able to function from this switch, the switch will need to have an extra gang on it for the lamppost, you will need to run SWA cable to the lamp, do some calculation on voltage drop on the length of cable, so the required cross sectional area can be chosen.
You will also so need a neutral conductor at switch, don't be fooled by thinking blue or black cores are necessarily neutrals, quite often they are live/phase conductors when at switches.
I would also recommend that RCD protection was given to the outside equipment.
The black band running around the bottom of your render, looks like bitumen paint, this area is often protected against damp and a 'damp proof course' could well be found about 150mm up from the outside floor level.
It would also be wise to consider a double pole switch for the functional lighting, this will help isolate that part of the circuit that is external and prevent continued nuisance tripping of the internal part of the circuit, if an external fault should appear. But this can only be done if a neutral is at the switch plate.

 

[SimonH2]

Bear in mind that this is notifiable work - and it will probably be cheaper to employ a spark than to pay your LABC fees.

 

[ban-all-sheds]

He'll almost certainly be happier for Dandy to dig the trench than be paid by Dandy to dig it himself.

 

[ToolbeltDandy]

Thanks for all the information. I will comply.

Would I need to chisel away the render to hide the cable inside? Is there some conduit I could afix to the wall and then render over? I know that the holes in the wall will be at an angle to prevent water ingress.



or

 

[Lectrician]

Take a photo of behind the switch and we will tell you if you can take your feed from there or not.

It is up to you if you want to chisel the wall out inside. It is not common place to chisel the wall outside.

 

[ToolbeltDandy]

Hey. Thanks. I won't be going home until Christmas but I'll take those photographs then.

The reason I want to chisel, is to avoid having a length of cable running along the outside of the wall, since I think it will be a bit of a blemish on the wall. I realise that after patching the render, I'd need to paint the whole wall to get it all the same colour, but I think that's worth it to hide the cable.

 

[bernardgreen]

It is not common place to chisel the wall outside.

And for good reasons

How will you mark the route of the concealed cable to prevent someone from damaging it if the wall is repointed or for some reason drilled ?

Chiselling the outside of the wall and thus breaking the "skin" of the bricks may allow the ingress of (more) water into the wall when it rains.

A visible cable can painted the same colour as the wall to reduce its visibility but still be there as a reminder that there is a cable going underground at that point.

 

[mfarrow]

I wouldn't want to ruin the render, you'll never get the pattern back.

Running the cable inside (option B) would be my best bet. If it's not being fed of the switch though, you'll need to put the cable in steel conduit or put suitable mechanical protection over the top (i.e. 3mm plate).

You can then run the cable to a low point as per option B and adapt to SWA for the outdoors run.

 

[ToolbeltDandy]

Follwing my investigations I find that all sockets appear to be covered by an RCD at the consumer unit and that the existing external light is on the same circuit as the kitchen sockets.

Click images for larger view.







Am I right in thinking I need to chisel away the plaster below the switch to the point at which I want the cable to exit? I have a rotary hammer - is that appropriate or will it cause too much damage? Then drill a hole through the brick to the outside of the house for the cable to go through. What are the options for sealing the hole around the cable? Does it get sealed on both sides?

The red line in the image below indicates the probable line for chiseling.

 

[SimonH2]

Yes, I'd suggest the neatest route would be to chase down the inside wall (as your red line goes), put a flush box* in there (cover it with a blank plate) and then go through the wall.
If you put a white oval conduit in, the cable can be added later (or replaced if needed).

Using a box does three things :

1) It gives an easy way to transition between the vertical run down the wall and the horizontal run through the wall. The alternative would be to put the cable in and then plaster over it - with zero chance of replacing it without hacking the plaster out should it ever get damaged.

2) Depending on the cable you use and the size of the hole, it means that you can avoid joints outside. Ie, bring your cable up into the outside box and without cutting it, feed it through the hole so it comes into the box inside - where you can join it to the T&E fed down from the switch.
You'll still need to gland off the wire armour of an SWA cable, but you can keep the inside part unbroken until it's inside the house. It'll need a large hole though - big enough for the cable and a separate earth cable for the SWA armouring.

3) By having a plate there, it should alert anyone drilling into the wall at a later date that there may be a cable around. It's below the existing switch so is already in a safe zone, but someone drilling under the counter may miss the significance of that.

* Like the one the switch is fixed to.

 

[ToolbeltDandy]

Hi. I found some information here which tells me to use nails to hold the conduit or channel in place before plastering over the top. Why nails and not say, screws with appropriate fixings? The nails go into the mortar joints right? Presumably y'all know what you're doing but hammering a nail into mortar doesn't feel right to me. I'm expecting the mortar to crumble whilst I hammer it and the nail to fall right out...

 

[Lectrician]

Nails, because it's quick and easy. Use plugs for the nails if the wall is suspect. It's only to hold it while plastering.

Use galvanised nails or if you use screws, use drywall screws or stainless steel. Using anything else can cause rust spots through the plaster when dry.