Electrical wiring system

Introduction

Modern vehicles have very long and complex electrical wiring system in them. If all the wiring length could be measured, it would be a mile or so. Modern cars technicians must have good knowledge of electricity and reading electrical schematic diagrams and circuit diagram is essential skill for them. To cope with electrical problems good knowledge of drawing reading and testing is a must. Without understanding electrical system and wiring of a car, repairing a car could be very much difficult and would become a nightmare. Understanding different symbols used on electrical schematic diagrams would help a lot a technician working on automotive systems. A technician must be aware of the current flow through the system and he must be aware of using appropriate size and gauge of wire to be used in a specific location and circuit to ensure proper current flow without heating up the wire due to excessive current flow. A technician can cause very easily a serious problem to the automotive system by using wrong size and gauge of wire. The technician must be aware of the three factors influencing wire resistance. Those three factors are length of wire, diameter of wire and temperature of wire. Longer the length of wire, higher the resistance of the wire, thicker the diameter of the wire, lower the resistance of the wire. Higher the temperature of the wire, higher the resistance of the wire. With this consideration in mind a technician would not make a mistake and would be able to repair the car wiring system efficiently and effectively.

Automotive wiring types

There are two types of automotive wiring. Fist is primary wiring and second is secondary wiring. The primary wiring term is used for wiring in which wire carry current and low voltage is applied to them. There is 12v or 24v low voltage is normally used in automotive. So the part of wiring working on low voltage would be primary wiring. For primary wiring lower grade and thin insulation is used as low voltage don’t need much thicker insulation. The secondary wiring is that type of wiring which carries current and high voltage is applied to those wires. For example spark plug wires. For ignition system extra high voltage is applied of spark plugs. The wires carrying the ignition system current under high voltage have extra thick and special insulation to bear such high voltage.

Primary wire conductors are usually made of several strains of copper conductors twisted together. Several strains provide more conductor surface area and also makes the wire flexible. The insulation of the primary wires is normally thin as they face low voltage. The insulation is usually polyvinyl chloride or PVC. Some wires have another protective layer over the insulation.

Copper is commonly used because there is no other better substitute material compared to copper as it has lower specific resistance, flexibility, durability and easy availability. Other conductive materials like silver, gold, aluminum and tungsten are also used occasionally but they are not commonly used for making wires.

Wires used in automotive wiring are normally strand wires. Strand wires are those wires which are made of several strains of thin copper wires. These strains are twisted together to make a wire of them. Then these stains are insulated to make cables of them. Strand wires have less resistance than solid wires and they are very flexible. They offer less resistance because of skin effect. The electrons tend more to move on the surface than in the center of the wire. Strand wires have more surface area compared to the solid wire. This is because each strain in the wire has its own surface area which would become larger surface area compared to the same size solid conductor surface area. That is why the strand wire offers less resistance or impedance compared to the solid wire.

PVC insulation is used because it can withstand temperature extremes and it is inert with copper and don’t corrode copper. PVC insulation can bear acid, gasoline and anti-freeze. It is not reactive with such materials present in automotive and cars. The insulation has a very important purpose. It prevents the wire from shorting to ground as well as it prevents is from shorting to other circuits.

Wire Sizes

Selection of appropriate size wire for a certain circuit is very critical. The wire size selection is important to make the wire suitable for the current flow, durability, less voltage drop, less temperature emission and acceptable resistance. Following three considerations must be kept in mind when selecting wires for a specific circuit.

1.       Wire have enough thick diameter for the required length to carry certain amount of or current to the load without dropping voltage from the specified voltage drop limit to ensure proper operation of load.

2.       Wire used for a specific circuit should bear the amount of heat it is exposed to.

3.       Wire must be able to withstand certain value of vibration it will be expose to. Because in automotive vibration is a very common factor all parts expose to.

Wire size determines the amount of current flow through the wire. Larger diameter wire has less resistance and more current carrying capability. Lesser diameter wire has high resistance and have lower current carrying capability. There are two standards to measure the wire size. American wire gauge and standard wire gauge or matric. American wire gauge is AWG and standard wire gauge is SWG.

American wire gauge and standard wire gauge are designating numbers to different diameters of wires. The higher the number of AWG or SWG, the thinner the wire. The lesser the number, the thicker the wire. For example a 22AWG wire would be thinner than 12AWG wire.