Garden Lighting - advice/guidance needed

[richards1978]

Hi,

Before going through the length and costly process of notifying Building Control of my planned garden work.
I was wondering if I could sound my idea on this forum, and see what everyone thinks.

I have a CU in my garage, that I am planning to use to run lighting into my garden.
The garage CU is run from a sub-main from the house CU, and is RCD protected by the house CU.

I was planning to put a new 6A MCB in the garage CU and run 2.5mm cable to a DP switch. I was then planning to use 2.5mm SWA from this switch to take the power outside, by clipping it to the garage and house walls to an adaptable box on the side of the house. The plan was then to use some additional SWA to take the live connection to a weatherproof light switch by the back door, and back to the box.

A further length of SWA would then take the power through existing ducting under the patio to the first garden light. I'd then daisy chain the cable around the garden to the other lights (9 in total) running it through ducting, which would be about a 50m of cable all in.
The ducting is already in place running to where the lights would go, and is about 2 foot deep, with the necessary warning labels over it.

The SWA would all be 3-core, and I'd use the black wire as the earth, and the grey wire as the neutral connections, and sheath them accordingly.
I'd also earth the armour in the SWA at each junction using a banjo attached to the SWA glands.

Is there anything obvious I'm planning to do wrong, or can anyone spot any issues what what I'm suggesting?
Feel free to be as merciless as you want in picking faults with the above, as the last thing I want to do is get torn a new one by building control after forking out for their insepction fees.

Thanks
Rich

 

[ban-all-sheds]

Wouldn't going straight to the light switch be better than all that back and forth to the box?

You've got lights you can get 2 SWA glands into?

What testing do you plan to carry out on the new circuit?

 

[sparkybird]

Why are you using 2.5mm SWA on a 6A breaker? Assuming each light is no more than 100W (and if they are then your garden will be like Blackpool Illuminations!) 1.5mm will be fine and much easier to handle/terminate, plus much cheaper!

 

[flameport]

I'd also earth the armour in the SWA at each junction using a banjo attached to the SWA glands.

A much easier way is to use a plastic junction box at each light position, which is internally fitted with one of these:
http://www.tlc-direct.co.uk/Products/WKEC308.html

or alternatively a metal box like this:
http://www.tlc-direct.co.uk/Products/CO20BXYG.html

and then have a short piece of flex from the box to the light fitting, connected to the box with a suitable gland.

 

[richards1978]

Thanks for all the replies, guys.

Wouldn't going straight to the light switch be better than all that back and forth to the box?

I did measure up, and because the switch would be quite out of the way from both the garage power supply and the first light, I'd have to run more cable and double it back on itself if I went straight to the switch and then to the first light.

You've got lights you can get 2 SWA glands into?

This is the bit I'm struggling with. I did consider using a Y-box like flameport suggested. The lights I want to fit have a reasonably sized cone on the base, but its not big enough to get a box under the light without cutting down into the wall a bit to make more room - do-able, but are there any other alternatives?

What about having a thick plastic plate attached to the wall under the light, and having the SWA terminate unto these. Would there be any issue doing this?

It's not the best diagram, but something like this:

What testing do you plan to carry out on the new circuit?

This is where I need to check with the council what they will be doing as part of their inspection, as I think you need to be classed as "competant" for any testing to be valid.

Why are you using 2.5mm SWA on a 6A breaker? Assuming each light is no more than 100W (and if they are then your garden will be like Blackpool Illuminations!) 1.5mm will be fine and much easier to handle/terminate, plus much cheaper!

Point taken, I was trying to make it "future proof" in the event I wanted to extend the circuit later, but looking at the voltage drop calcs it looks like 1.5mm would be more than enough.

 

[Electrifying]

........ looking at the voltage drop calcs it looks like 1.5mm would be more than enough.

You haven't told us how long, (and what CSA), the submain to the garage CU is and what the loads are on this submain (including your garden lights).

Volt drop is calculated from the origin so any chance of seeing your calcs?

 

[richards1978]

........ looking at the voltage drop calcs it looks like 1.5mm would be more than enough.

You haven't told us how long, (and what CSA), the submain to the garage CU is and what the loads are on this submain (including your garden lights).

Volt drop is calculated from the origin so any chance of seeing your calcs?

Hi,

Sorry didn't state the CSA of the submain to the garage as we got the electrician to fit it well over spec for the current requirements (wanted to keep it future proof if we ever wanted garden lights, outside sockets, car, hot tub etc). I think it's 16mm (its huge) - I will check this for certain before submitting any part P applications.

The main house CU is on one side of the kitchen, and the garage is on the other so it only runs about 5-10m from one CU to the next.

I cheated with the calcs, and used this:
http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

I based the calcukation on 60m cable length, running 1kw in underground PVC 3-core SWA.
It came back as 1.5mm, but I was going to go for 2.5mm in case I wanted to extend the lighting later.

 

[richards1978]

Thanks for all the comments and suggestions so far. Was wondering if anyone has any other points to make before I notify the council and make plans to do something stupid/illegal/costly.

Cheers