Colour in the table
Colour in the table
Purpose of a Fuse A fuse is to protect the device as well as the wiring. A good example of this is a fuse in a wiper motor
circuit. If a value were used, which is much too high then it would still protect against a severe short circuit. However, if the wiper blades froze to the screen, a large value fuse might not protect the motor from overheating.
Fusible Links Fusible links in the main output feeds from the battery protect against major short circuits in the event of an accident or error in
These links
wiring connections. These links are simply heavy- connect to the
battery
duty fuses and are rated in values such as 50, 100 or 150A.
Circuit Breakers Occasionally circuit breakers are used in place of fuses, this being more common on heavy vehicles. A circuit breaker has the same rating and function as a fuse but
A bimetal strip is the
with the advantage that it can be reset. main component
Terminals and Connectors Many types of terminals are available. These have
developed from early bullet type
Selection of
Terminals and
connectors into high quality waterproof terminals and connectors in
connectors
use
systems now in use. A popular choice for many years was the spade terminal. This is still a standard choice for connection to relays for example, but is now losing ground to the smaller blade terminals. Circular multi-pin connectors are used in many cases; the pins varying in size from 1mm to 5mm. With any type of multi-pin connector an offset slot or similar is used to prevent incorrect connection.
Protection Protection against corrosion of the connector is provided in a number of ways. Earlier methods included applying suitable grease to the
Waterproof
pins to repel water. It is now more usual to use connector block rubber seals to protect the terminals although a
small amount of contact lubricant can still be used. Many multi-connectors use some kind of latch to prevent not only individual pins working loose but also to ensure that the complete plug and socket is held securely.
Wires Cables or wires used for motor vehicle applications are usually copper strands insulated with PVC. Copper, beside its very low resistance,
Cables in a
has ideal properties such as ductility and wiring harness malleability. This makes it the natural choice for
most electrical conductors. For the insulation, PVC is ideal. It not only has very high resistance, but also is very resistant to fuel, oil, water and other contaminants.
Cable Size The choice of cable size depends on the current it will have to
carry. The larger the cable used then
Heavy duty
Light duty
the better it will be able to carry the cable
cable
current and supply all of the available voltage. However, it must not be too large or the wiring becomes cumbersome and heavy! In general, the voltage supply to a component must not
be less than 90% of the system supply. Cable is available in stock sizes but a good ‘rule of thumb’ guide, is that one strand of 0.3mm diameter wire will carry 0.5 amps safely.
UK Colour Code The UK system uses twelve colours to determine
the main purpose of the cable. Tracer colours further define its use. The main colours used and
some other examples are given in
the table. European System A ‘European’
system used by Ford, VAG, BMW
and other manufacturers is based broadly on the following table.
Please note that there is no
connection between the ‘Euro’
system and the British standard colour codes. In particular, note the use of the colour brown in each system!
Terminal Numbers A popular system is the terminal
designation. This helps to ensure correct connections are made on the vehicle, particularly in after sales repairs. It is important
however to note that the designations are not to identify individual wires but are to define the terminals of a device. Listed here are some of the popular numbers.