Cable Sizes and Wiring
What ties all the components together in an electrical system are the cables. Cables supply the
power from power sources for distribution to appliances, lights and equipment. Unfortunately,
the most common installation error is to under-size cables relative to the load/s or from the
recharge sources.
Proper installation is primarily a matter of sizing a cable to match its task, using the correct
tools to attach terminals, and providing adequate over-current protection with fuses and circuit
breakers. Cable sizing is fairly simple; it is a function of the length of a cable measuring from
the power source to the appliance, and the current (amperage) that will flow through it.
The longer the cable, or the higher the amperage, the bigger the cable must be to avoid
unacceptable voltage losses. There should always be plenty of extra margin for safety because
an appliance may actually use more current than what it is rated for because of heat, low
voltage, extra load, or other factors. There’s never a performance penalty if a cable is
marginally oversized; there is always a performance penalty - and possibly a safety hazard - if
it’s undersized.
The ground (negative) cable is as much a part of a circuit as the positive cable; it must be sized
the same. In general, each appliance should be supplied from the distribution panel with its
own positive and negative cables, although lighting circuits sometimes use common supply
and ground cables to feed a number of lights (in which case the supply cables must be sized for
the total load of all the lights). For 24v systems, the cables size is half that of a 12v setup.
Always read product recommendations, or check with the supplier to know and understand
exactly what size cable is required for the products.
To better plan and size cables, please reference the cable sizing table below:
Circuit Type DC Amps
10%
3%
Voltage 5A 10A 15A 20A 25A 30A 40A 50A 60A
Voltage
Drop
Drop
(Non-
(Critical)
Critical)
0-6 m 0-2 m
6-9 m 2-3 m
9-15 m 3-4.5 m
15-19 m 4.5-6 m
19-24 m 6-7.5 m
24-30 m 7.5-9 m
30-40 m 9-12 m
40-51 m 12-15 m
Cable
Length
51-61 m 15-18 m
in
Meters
18-21 m
21-24 m
24-27 m
27-30 m
Circuit Type DC Amps
10%
3%
Voltage 5A 10A 15A 20A 25A 30A 40A 50A 60A
Voltage
Drop
Drop
(Non-
(Critical)
Critical)
30-33 m
33-37 m
37-40 m
The above cable sizing table is used by running across the top row until the column with the
relevant amperage is found, and then moving down the left-hand column until the row with
the relevant distance is reached. Wire sizes are denoted by colour coding.
Gauge:
A common way for referencing a cable size is its “gauge.” The American Wire Gauge (AWG) is
used as a standard method of denoting wire diameter, measuring the diameter of the
conductor - measured as only the bare wire with the insulation removed. AWG is sometimes
also known as Brown and Sharpe (B&S) Wire Gauge.
Below is a conversion chart from AWG/B&S to mm². This table gives the closest equivalent size
cross references between metric and American wire sizes. In Europe and Australia, wire sizes
are expressed in cross sectional area in mm².
Standard Unit
AWG 0000 000 00 0 1 2 4 6 8 10 12 14 16
Diameter (mm) 11.68 10.40 9.27 8.25 7.35 6.54 5.19 4.11 3.26 2.59 2.05 1.63 1.29
Standard Unit
Cross Section (mm2) 107.1 84.9 67.5 53.5 42.4 33.6 21.2 13.3 8.4 5.3 3.3 2.1 1.3
Colour Code
A printable guide to sizing cables can be downloaded here.
Title
Guide - Cable Sizing Chart
File
Colour Coding
While is possible to use the same cables for AC and DC circuits, it is advisable to use different
coloured cables between the two types of currents, both to increase handling safety but also to
make installation and repair work much faster. If existing appliances or installations have
colours, logistics managers may consider replacing or standardising them by re-colour coding
the wires with an external paint or marking in a method that makes sense.
A general colour cod for AC looks like:
Neutral: Blue.
Phase: Brown or black.
Ground: Green/yellow.
The neutral and the phase are the two connections for the electricity, the ground is for safety.
Colour code for DC (direct current, battery):
+ = red or blue
- = black or brown
Many differing international standards apply however. Please reference the below table for
colour coding of different countries and regions around the world.
Standard Wire Colours for Flexible Cable
(e.g. Extension Cords, power cords and lamp cords)
Protective
Region or Country Phases Neutral Earth/Ground
European Union (EU), Argentina,
Australia, South Africa
, ,
Australia, New Zealand
,
Brazil
(green) or
United States, Canada
(brass) (silver)
(green/yellow)
Standard Wire Colours for Fixed Cables
(e.g. In/On/Behind the wall wiring cables)
Region or
Phases Neutral Protective Earth/Ground
Country
Argentina
, ,
European
Union and UK , ,
UK Prior to
March 2004 , ,
(formerly)
Any colours other than:
, , ,
(since 1980)
Australia, New Recommended for single-phase:
or
Zealand (since 1980)
Recommended for multi-phase:
bare conductor, sleeved
at terminations (formerly)
, ,
, , ,
Brazil
, or
South Africa
, bare conductor, sleeved
at terminations
India, Pakistan
, ,
, ,
(green)
(120/208/240V) (brass) ,
(120/208/240V)
United States , (Silver) bare conductor
(277/480V) (ground or isolated
(277/480V)
ground)
,
(120/208/240V)
(green)
, ,
(600/347V) (120/208/240V)
Canada
bare conductor
,
(single-phase isolated systems) (600/347V) (isolated
ground)
, ,
(three phase isolated systems)
Important points to note when wiring:
All circuits should be removed from the floor and be as high as possible with no
connections in or near water or damp areas.
All cable lug connections should be securely crimped to the wire termination with a band,
and not soldered in place.
Tinned cable – copper wire that has been coated with a thin layer of tin to prevent
corrosion - It is preferable to use where possible in a marine environment or near salt
water.
Never tap into or splice existing circuits when installing new equipment; run a properly
sized new duplex cable (positive and negative cable in a common sheath) from the
distribution panel (or a source of power) to the appliance.
It is recommended to label all cables at both ends, and to an updated wiring plan to aid in
future troubleshooting. Copies of the wiring plans can be even be stored in locations such
as the fuse box or distribution box so that future users can reference them.
Each circuit should have an independent ground cable, and all the ground cables should
eventually be tied back to a common ground point/busbar.
Unless in a conduit, cables should be physically supported at least every 450mm.
Although black is often used for DC negative, it is also used for the live wire in AC circuits
in the USA. That means there is potential for dangerous confusion. DC and AC wiring
should be kept separate; if they have to be run in the same bundle, one or the other
should be in a sheath to maintain separation and ensure safety.
