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.
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.
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!
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
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
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
. . .
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
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:-
÷ Volts= Amps
i.e. 48 Watts ÷ 12 volts = 4 Amps (plus the 35% safety
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:
Mate - distributor.
Store online distributor
There are many more of course - just do a Google! Search for
"wire AWG cable electrical distributor". You will
be spoilt for choice!
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
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
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.
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Other pages to help you with
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Warming - it's why we are making changes to our way of life!
David Bellamy has a very interesting article on global warming
where he gives another point of view, Read