240V Soffit light wiring - best practice wire paths?

[Globs]

Hi,

I'm wiring in 5 soffit lamps that I'll want off two circuits, in a new roof that has not been felted yet.

Ideally each lamp will be connected via a single 1A solid T&E cable, but should I route these 5 individual wires into the loft space for junction box connection - or should I put the junction boxes into the soffits to save cable?

Also how should I route the wires - just use nail/cable clips every 0.5m to route them up the centre of each rafter?

The switches would ideally end up on the wall and switch from the lighting circuit, so either way I'll need to get back to a wire to be routed down the wall in a channel.

Thanks in advance!

 

[riveralt]

Just to start - plastic soffits and downlights do not make good partners - as the downlights get hot the plastic will turn yellow.

While there is not a Part P element to this installation, provided there are no exposed outdoor connections and the work does not involve the installation of a new circuit, the work will still have to comply with the BS7671.

Given your description of what you intend (would like) to do are you sure you have the knowledge and competence to design, install and test this work yourself?

What do you mean by 1A solid T&E cable?
Junction boxes can be used provided they are accessible.
Are the lights you are getting intended for outdoor use and what is their IP rating and wattage?
How many lamps are already on the lighting circuit you intend to use?
You say you want the lamps off two circuits, if the lighting circuit is one what is the other?

I really think you need to do some more research on how lighting circuits work, looking on wiki would be a good start.

 

[Globs]

Thanks for the reply Riveralt, info as follows:

1) Downlights have to be LED as building regs requires energy saving bulbs and I do not want to fit CFL so it will be LED - probably up to 3W each.

2) 1mm twin and earth - the regular stuff for house wiring, i.e. not flex.

3) All stuff is subject to Part P inspection and full building regs as this is for a new extension.

4) I have rewired a house before (before Part P) and am familiar and experienced with house earthing systems, house electrics, vehicle electrics, electronics and high voltage tube electronics. Good question though as you don't know me from Adam

5) All noted about accessibility - that answers the question, all cables have to terminate in the loft space then!

6) Downlight containers are for external, fire rated and comply to part B C and E

7) One switch will control 3 lights, a second will switch the other two. Both off the same live feed from the lighting circuit for that level. I.e. a fitting with two switches in.

So I guess the remaining question is what's the best practice to route the cables from the lighting points to the loft? Would you run them straight into the loft then across clipped to the rafters, or route them along the soffit hopping through holes in the rafter overhand and then up as a bunch?

 

[riveralt]

So I guess the remaining question is what's the best practice to route the cables from the lighting points to the loft? Would you run them straight into the loft then across clipped to the rafters, or route them along the soffit hopping through holes in the rafter overhand and then up as a bunch?

Given the propensity for gutters leaking/overflowing and birds nesting in soffits - I would want to get the cable into the accessible loft area to the jb as soon as possible. Remember you will have to wire the LED's as per manufacturers instructions.
Remember that you LED lamps, if not incorporated already, will need LED drivers so you will want to do the same with them.
Once inside the loft area how you run the cables from the energy source and to the light switch is up to you. Your only concern will be to avoid the loft insulation.

Oh and I assume the circuit will have additional protection of an RCD.

 

[Globs]

Hi, thanks for the info.

The LEDs are GU10 240V LEDs so I think that will be straightforward - but it does mean the wires carry 240V.

The lighting circuit is not on the RCD side of the panel - do I need to put these lamps on an RCD'd circuit?

 

[riveralt]

Hi, thanks for the info.

The LEDs are GU10 240V LEDs so I think that will be straightforward - but it does mean the wires carry 240V.

LEDs require an LED driver which will be incorporated into the lamp itself or form part of wiring. The manufacturers instructions that come with the lamp should explain this.

The lighting circuit is not on the RCD side of the panel - do I need to put these lamps on an RCD'd circuit?

The rules regarding RCD's can be complex and will depend on a number of factors including a high earth fault loop impedance measurement, often but not always associated with TT installations, the depth of the cable from the surface must be greater than 50mm and others.
If you do not have a high EFI and the cable is greater than 50mm from the surface then you may not need utilise an RCD. The whole idea is to stop people banging nails or screwing screws into hidden cable, which is why you do not need an RCD when the whole of the cable run is surface mounted.
There is nothing to stop you using a socket circuit to provide power to your leds. Again the LED Manufacturers instructions will say what they expect, but if you spur from a socket through a FCU (3Amp maybe) to your lights and light switch your circuit should already be protected by an RCD.

 

[Globs]

Hi,

The house system is TNS which makes it quite simple.

The LEDs take 240V at the pins so the driver (SMPS) is inside the GU10 body.

Wiring should be at least 75mm away from the soffit as the lamp can is about 4" tall and the wire will just jump from there to the rafter with some slack to allow the can to be pulled out it required. I'll double check with the building inspector though!

I could use a socket circuit I guess - although not a ring, I just hate wiring multiple wires into lamp fittings and usually go for a junction box instead. In this case however perhaps it would be neater.

 

[Lectrician]

Wiring should be at least 75mm away from the soffit as the lamp can is about 4" tall and the wire will just jump from there to the rafter with some slack to allow the can to be pulled out it required. I'll double check with the building inspector though!

I could use a socket circuit I guess - although not a ring, I just hate wiring multiple wires into lamp fittings and usually go for a junction box instead. In this case however perhaps it would be neater.

What about the switch drop? You mention this is to be ina chase in the wall - This will generally require RCD protection.

If you did supply these from the ring, what would stop you using a joint box? I don't understand what you mean.....

Who is wiring the extension itself?

 

[Globs]

Wiring should be at least 75mm away from the soffit as the lamp can is about 4" tall and the wire will just jump from there to the rafter with some slack to allow the can to be pulled out it required. I'll double check with the building inspector though!

I could use a socket circuit I guess - although not a ring, I just hate wiring multiple wires into lamp fittings and usually go for a junction box instead. In this case however perhaps it would be neater.

What about the switch drop? You mention this is to be ina chase in the wall - This will generally require RCD protection.

If you did supply these from the ring, what would stop you using a joint box? I don't understand what you mean.....

Who is wiring the extension itself?

So do the current regs specify every (new) switch drop must be on an RCD now? I.e. Does this mean the old house lighting circuit (which will be used to connect the new extension lights - and is not on an RCD) need to be moved to an RCD?

If so - a) crikey, and b) why do they mandate that now?

I was going to position the cables to connect the soffit lighting to the lighting circuit at the same level, and hook in via a junction box to also drop a switch wire down (conduit on wall then plastered over).

The main extension wiring is just an extension of the socket rings and lighting circuit so I'll do that and get it inspected or perhaps 2nd fixed and inspected. Please note these questions are only first fix related - I.e best practice for routing cables.

BTW as there seems to be a raft of new regs in the last decade where can I get a copy of the regs and perhaps also a book of best practice?

Also a question - say you were installing new soffit lighting using 4W LEDs - would you go for 240V GU10 or a 12V MR16 system (both 50mm bulbs), and why?

 

[riveralt]

So do the current regs specify every (new) switch drop must be on an RCD now?

The answer is yes, unless buried 50mm below the surface or otherwise mechanically protected.

I.e. Does this mean the old house lighting circuit (which will be used to connect the new extension lights - and is not on an RCD) need to be moved to an RCD?

Yes that is correct unless.....as outlined above.

The main extension wiring is just an extension of the socket rings and lighting circuit so I'll do that and get it inspected or perhaps 2nd fixed and inspected. Please note these questions are only first fix related - I.e best practice for routing cables.

The extension will have to be included with RCD protection unless....as outlined above.
Who is going to inspect the installation?
Who is going to test the installation?
Who is going to give you the Electrical Installation Certificate?

BTW as there seems to be a raft of new regs in the last decade where can I get a copy of the regs and perhaps also a book of best practice?

Start with the On site guide - this is the old version (red) a new one (green) will be out shortly - but most of what you need will be in the red book.
Also consider the Electricians Guide to the Building Regulations.

http://www.amazon.co.uk/Electricians-Building-Regulations-Electrical-Dwellings/dp/086341463X

 

[ricicle]

I take it these are new soffits. Older ones could be made of asbestos.