Wiring sizes and their usage is so critical that this whole page has been dedicated to it. This is where mistakes can be easily made, and the consequences of getting it wrong are dire - So make sure your ready for a little detail.

Warnings and disclaimer If you are in any doubt of your own ability then consult a qualified electrician with knowledge of 12 volt solar systems.

There are quite literally catalogues full of different sizes and types of wire, but there are wires that are better at specific jobs than others and here we will talk about wiring for 12 volt DC circuits such as are found in cars, caravans, boats, planes and of course solar systems.

Wire Type
Electrical wire will have one of two types of conductor, that's the central metal wire core - the first type is a single stranded conductor and the second type is a multi stranded conductor.


An example of multi stranded wire is illustrated below - whereas the single core conductor is just one single strand, typically used in domestic wiring and doesn't need a picture as I am sure you will be familiar with it. Quite frankly you would not be reading this page if you were not!

Green = Ground Black = Negative Red = Positive

The main reason for multi stranded conductors is for installing into systems that may suffer from vibration probably because they are in equipment that is mobile, such as in aircraft, boats or vehicles to name just a few examples. The benefit of the multi strand is that unlike the single strand it performs better under continuous vibration. Whereas the single strand wire possibly can weaken and fracture under those conditions.

Wire and cables are all rated and have a maximum current rating that must not be exceeded.

Wire is rated according to current rating (Amps) that can safely pass along it, the higher the current the thicker the wire. It is critical to get this RIGHT.

Lets just talk briefly about what can go wrong in principal - if you attach an appliance to an under rated cable (to thin that is - or too long!) the voltage will drop and then the cable will heat up and eventually may catch FIRE.

OHMS LAW SAYS - When the voltage goes down the current goes up.

Think of your wiring like a piece of plumbing, if you tried to force water under pressure through a pipe and then tried to greatly increase the flow and pressure, the pipe would eventually burst, and the only solution to this problem is to get a bigger bore pipe and the problem is solved.

And that is the same for wiring, of course the wires don't quite burst, THEY CATCH FIRE. More or less for example, like the bar of an electric fire.

Decisions about wire thicknesses are generally related to cost and are closely specified by the professionals, but often for the smaller projects like solar buying a reel of thicker wire to cope with the biggest current appliance you will be using, and then using it for all other individual runs to the fuse box can be a beneficial decision and here is why . . .

Voltage Drop
If you have a long wiring run and are wanting to connect a fairly high current (Amps) appliance to the end using a too closely matched cable then their will be likely a voltage drop!

i.e. if you have a 15 amp appliance and run it through a15 amp wire then you are at risk, allow at least a 35% margin so fit something like a 25 amp wire. It's all about safety, why under rate, there is only pence in it!

So what exactly is happening to the wrongly and too closely matched 15 amp cable, putting it simply it is warming up enough to cause the voltage to drop, maybe not enough to catch fire, but we all know what direction we are now heading in! So go bigger on the wire thickness than you need. Now you see how cost can come into the equation, if you had a big circuit to specify you would be upping and downing the wire thickness to save some money. Also remember that if you add any new appliances later on, you must consider their current ratings in relation to your wire rating you used originally. It's all about common sense!

Example: How do you find out the current (Amps) of an appliance?

Suppose you have a 12 volt 48 watt TV to wire into a circuit, you can quite simply apply Ohms Law:-

             Watts ÷ Volts= Amps

i.e. 48 Watts ÷ 12 volts = 4 Amps (plus the 35% safety margin) -

So a 5.5 Amp wire (or preferably a bit bigger Amp rating - Example: 6 Amp, AWG 12 for a 4.6m length) from the fuse box to the TV would be fine. If you want a longer run then see the wire guide below.


The Wire Gauge Guide Below is a Quick Reference for Choosing the Correct Wire Thickness

** Please consult your local electrical trade distributor for the correct cable for the current you will be carrying on it. They are generally very helpful and knowledgable with this very important point - just be armed with the amps (current) you will be drawing in your circuits.


Solar Panel Wire Distributors:

QVS Electricians Mate - distributor.

Power Store online distributor

Maplins

BDC

There are many more of course - just do a Google! Search for "wire AWG cable electrical distributor".

Here is a guide (and I mean a guide only - see above **) to wire gauges - just read off the Amps on the left column and scan across to the length of your runs. Then go up the column to the AWG (AWG is a USA system still widely used) number. NOTICE that the AWG numbers decrease as the wire gauge thickness goes up!

AWG	12 3mm²	10 5mm²	8 8mm²	6 13mm²	4 21mm²	2 32mm²
4 Amps	7m	11.1m	17.7m	28.2m	44.9m	71.4m
6 Amps	4.6m	7.4m	11.8m	18.8m	30m	47.7m
8 Amps	3.5m	5.6m	8.8m	14.1m	22.5m	35.7m
10 Amps	2.8m	4.4m	7.1m	11.3m	18m	28.5m
12 Amps	2.3m	3.7m	5.9m	9.4m	14.9m	23.7m
14 Amps	2m	3.2m	5.1m	8.1m	12.8m	20.4m
16 Amps	1.7m	2.8m	4.5m	7m	11.2m	17.8m
18 Amps	1.6m	2.5m	4.0m	6.3m	10m	15.9m
20 Amps	1.4m	2.2m	3.6m	5.6m	9m	14.3m
25 Amps	1.1m	1.8m	2.9m	4.5m	7.2m	11.4m
30 Amps	0.9m	1.4m	2.4m	3.7m	6m	9.5m
35 Amps	0.8m	1.29m	2m	3.2m	5.1m	8.1m
40 Amps	0.7m	1.1m	1.8m	2.8m	4.5m	7.1m

One thing to remember though is that the individual runs to all appliances must be connected to a fuse box and distribution point, the wire supplying the distribution point from the battery(ies) however must be capable of carrying the total overall current of all the separate runs to the fuse box, plus a good 35% more - at least.

Always make good notes of your wiring gauges and keep a copy close to your fuse box for future reference. Say for instance you used 10 amp rated wire for all your runs, you could then state your system as a '6.5 Amp system on 10 Amp wiring' i.e. 10 amps less 35% at least = around 6.5 Amps. That sort of care and common sense will not let you down.




© 2007 solaratlas.com - All Rights Reserved

Other pages to help you with the installation are:-

	How to wire up a basic solar panel system Is your battery bank correctly wired up?
	The Big Live Solar Panel Experiment See how our 27w solar panel performs under live conditions
	Battery care
	Looking after a leisure battery
	Solar circuits
•	Coming soon selecting and fitting fuses to your solar system.

To communicate with us over technical issues please use the Solar Chat Forum, also take a look at the Solar Q&A page.

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