Calculating what you need for electrics

Apologies to my regulars who have heard some of this several times but for the benefit of a first time visitor it bears repeating.  Also, I am  trying to get all my electrical instructions in one place at last.

Round wire v. copper strip.....  there is no right choice here: use the system you feel comfortable with.  I use the round wire system because when I was doing my first project I was told by a super nice, knowledgeable chap that copper/tape wiring can have more problems if you intend to keep the house a long time.  The wires can deteriorate over time especially if they are covered in wallpaper paste and acid wallpaper.  You may not make good soldered connections so they too can be a weak point. sometimes if you move a house it can also break the wires.  If the whole lot 'blows' it is often hard to track the fault.  I am absolutely sure there are many people people who would refute this and wouldn't use round wire systems but that's how I arrived at my choice.

So, using the round wire system.......Most lights come with a two pin plug on the end of a wire which eventually, after weaving its way through your project, will exit and want to be plugged into one of these power strips.  That is then connected to a transformer then to your wall socket/electrical supply and you are good to go.

Reasons I don't use them....

• This strip will take twelve lights so on a large build you may need several of these. 
• I absolutely hate removing the little plugs on the lights to get the wires through the exit holes and then struggling to get them back on again on the other side
• They are a fair size and if you use several of them it is cumbersome
• The cheaper ones are notoriously unreliable

The power strip I use looks like this.... you can get it from Little Houses Plus and Small World Products

SWP Easy-Wire system Power Centre

Reasons I like it...

• This strip will take about 85 bulbs (note that's bulbs, not lights) so it has at least four or five times the capacity of the white plastic power strip
• No messing about with the fiddly plugs, the wires just go straight into the terminals
• It is smaller than one of the plastic strips and, for example, I would need two of those for this project
• It is well made and reliable.  It has at least a fifteen year life and can even be repaired if needs be 
• The terminals are numbered so you can make a list of what light has gone where
• You can easily attach flickering light power strips if you want flickering candle light or firelight
• They come in several capacities so there will always be one for your project
• There are ones with switches for each pair of terminals, so you can control areas of your build - lights on in any place you like while others are off if you want to

This power strip takes all the wires from your lights and then connects them to a transformer.

Your transformer needs to be 'large' enough capacity for the amount of lights you have.  Generally speaking a 3 amp, 12 volt transformer like this one will do for most people.  A well lit large project made need more Amps and therefore a larger transformer.

This is how you calculate what you will need for both of these units.

You need to know how many bulbs you have (not how many lights and fires you have) so if you have a grand twelve candle chandelier you set off with twelve and so on.  In a perfect world you should know how many bulbs screw in and how many push in.  I do think this is unrealistic and have never bothered calculating that accurately and have just gone for overkill.

A push in bulb uses 0.05 Amps and a screw in bulb uses 0.07 Amps.  So for this project I have 44 bulbs and if they were all screw in bulbs I would need a transformer able to cope with 3.08 Amps.  If all my bulbs were push in bulbs I would need something to cover 2.2 Amps.  As I have an unknown mix of these bulbs I am confident my 3 Amp transformer will be large enough.

As my bulbs add up to roughly 3 Amps I also need to change the fuse in the power strip as that is only a 2 Amp fuse.  That would cover roughly 34 bulbs.

OK - now I have blinded you with science and put you off for life let me just say you can just dive in and follow the instructions that come with your power strip and keep your life much simpler.  Here's the simple approach ......It says you can add up to 80 bulbs to the strip, as many as ten wires in each hole.  Work  out your amps by calculating 1 Amp for every 17 bulbs and you have it covered, change the fuse if you need to and you are good to go..

I have no intention, with this many wires, of rationalising and tidying them all up at the back of the house as I have done the past.  They will simply be taken to the power strip willy-nilly and eventually I will get a piece of thin ply cut and painted and fasten it to the back with magnets at each corner and all the wiring will be hidden in the wooden sandwich.

You will usually need some extra wire 

and some heat shrink tubing 

because some wires will need extending so they can reach your power strip.  I don't solder them!

I also have some lovely snips which cut wires neatly and strip the annoying plastic covering to expose the wire, so preventing tooth and nail loss and lots of cursing.  Invest if you can.

Come back tomorrow to see this lot in action