Sunday, 21 June 2015

Shed Electrics and low-Voltage Lighting ...


Firstly, a little quiz.    Take a look at this photo of these brand new light fittings I've bought, and the sealed boxes they came in, and see if you can identify what's wrong here....

can you see it ?

I only posted this photo because I thought it was so bleedin' obvious, and I just shook my head while muttering about the decline in educational standards, but then I showed it to a couple of other people.   

The first, like me, spotted it immediately but the second, after ten minutes of staring at it, still couldn't see anything wrong until it was pointed out to them....

Just in case, the answer's at the end of the post !



Anyway, back to the story.   We're running mains power to the new shed, and also adding to our low-voltage exterior lights by fitting another four LED spotlights, to illuminate the garden immediately in front.  We're also fitting lights inside the shed

The MR16 LED lamps we use for the exterior lights are typically 4-5W, and are directly interchangeable with the 50W halogens that are usually supplied with these type of lights.  The LED types are also 12V but work on either AC or DC, and the polarity is not important when used on a DC circuit.  We buy the day-white coloured lamps, which have a crisper and brighter light than the warm-white versions.

Similar to all the other low-voltage lights around the house, these new shed lamps will be illuminated automatically via a dusk-to-dawn photoswitch.  

We already have a 13A mains grade cable routed underground to our other shed just a couple of metres from the new one, but this cable is currently connected to the house exterior 12V circuit.  Under these latest modifications, this cable will be diverted to the new shed, connected to the 220V AC mains at the house, and then a 12V DC feed taken from within the new shed back into the old one, to drive the other four lights already fitted there in addition to the four we're adding to the new shed.

The mains diversion needs to be the last job of all, so that the existing lights on the old shed will continue to work until everything else is finished.

The lights around the house will still be controlled by the existing photoswitch on the house 12V circuit, but we'll need another one for all the shed lights.  We'll also need another 12V power supply unit in the shed. 

To summarise, we've currently 14 exterior spotlights all driven off the house 12V circuit, which is at the limits of its 6A power supply anyway.   In future, we'll have two independent systems, with 10 lights on the house circuit and 8 (initially) on a separate low-voltage circuit at the sheds.

So, on with the works - the first job was to install the new spotlight fittings, of which we've bought a job lot of six, see above, in enamelled pressed steel with swivel eyeballs for beam adjustment. 

After measuring and marking, it was out with the mains electric drill and the hole saw.  Cutting at a large diameter requires more torque than the cordless drills can deliver.


76 mm diameter hole saw....
The first hole was made through the board and then the light fitting pre-assembled with its spring clips ready for insertion.


hole in the upper front cladding board....

light fitting with spring clips fitted....

By holding the inner ends of the spring clip with one hand and squeezing the outers with the other, the fitting was aligned and pushed into the hole.   The spring clips hold the fitting firmly in place when installed. 


first one in place....

The other holes were then cut and three more fittings installed.


all four in place... 

The fittings were then wired-up internally, all in parallel, bringing each end of the power cables to a connector block screwed to the timbers close to each spotlight and with the silicone leads of the MR16 lamp connector attached.

The LED lamps were inserted from the outside and secured with the circlips, and an initial continuity check carried out on the wiring using a 12V battery to confirm all four lamps lit up.


with LED lamp fitted....
from the inside, showing wiring and the retaining clips on the fitting....

Next, onto the shed internal lighting.  I'd bought a 5 metre length of white LED waterproof striplight on eBay, and simply stuck it all along the length of the underside of the central roof beam.   I'm always wary of the quality of the self-adhesive tapes on the back of these things, so I've also clamped the strip to the beam every 500 mm or so.


striplight on the longitudinal beam...

Again, everything was tested using a 12V battery.


striplight LEDs and clamp.....

I wired up a standard light switch on the inside of the door post, and brought the cables to a terminal block near the striplight tails.


striplight end and terminal block....

The mains cable was then routed into the shed and terminated at a fused spur connection, from which I took a cable to a metal-cased double socket.   There's also a separate isolator at the house end of the cable.



incoming isolator in the shed....

The 12V DC power supply unit was fixed with screws to a vertical timber and connected to the mains socket using a standard plug with a 3A fuse.  Both the internal and external lighting cables were wired to the 12V output terminals.


12V DC 15A Power Supply Unit (PSU) ....

This 15A power supply was bought new, although I already had a spare 6A version which would have been enough for the eight external lights on this circuit plus the internal lighting strip.  However, the extra capacity will allow us to take off additional 12V feeds, maybe for extra garden lights (especially at Christmas) or for the wireless CCTV cameras we've set up occasionally at the bottom of the garden to watch the hedgehogs etc.


We already had the switched spur unit, light switch and the metal-cased socket, but we needed to buy a couple of plastic backboxes for the spur and switch.  We also completed the wiring just using odd lengths of cable we could find lying around, so there was no new cabling to buy which can sometimes work out quite costly for these sort of jobs.

So, a total cost of around £30 for the shed electrics.


The job's not quite finished yet - I'm still awaiting delivery of the 12V photoswitch I ordered a week ago and so the external lights are temporarily wired directly to the power supply, which means that we'll need to switch on the PSU at the socket late in the evening and switch it off again early in the morning, at least for the next couple of days or so.

To end the post, here's a few photos of the lights in operation.  It wasn't totally dark but late twilight, this being 10.30 pm on the longest day of the year...








Answer to the quiz above - they're octagonal of course, not hexagonal !


3 comments:

  1. Looks fantastic, nice job! It almost makes me want to try and fathom out/improve the electrics in our shed!

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  2. Thanks. If you already have a mains feed to the shed, then that's more than half the battle. We were lucky in that we'd laid a cable out to the 'old' shed a few years ago, and so it was very easy to divert this time.

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