Circuit Components
CONDUCTORSSubstances that have free electrons readily available are known as conductors. The best conductors are metals: gold, silver, copper, and iron. But it is important to remember that even good conductors have measurable resistance. Four main factors determine the resistance of metallic conductors:
1. The material itself; copper conducts better than iron for example
2. The length of the conductor; the longer the conductor, the higher the resistance
3. The cross-sectional area; the thinner the conductor, the higher the resistance
4. The temperature of the conductor; the higher the temperature, the greater the resistance
INSULATORS
All substances differ in their ability to conduct electricity. Some do not readily permit current flow. Such a material is called an insulator. The resistance to electrical flow by a substance depends on the scarcity of free electrons in its atomic structure. The materials that we know to be good insulators are made up of atoms that have few, or no, free electrons.They would include rubber, mica, plastic, glass, and air.
Low voltage, low current conductors usually use a thin plastic insulation unless they are located in an area of the vehicle where high temperature or other harmful conditions exist.
Conductors that carry high voltages use a more durable, high temperature resistant insulation that won't break down when the circuit heats up. Circuits that carry extremely high voltages, like spark plug cables, are covered with a very thick insulation to prevent the spark from jumping to the nearest ground.
Radio antenna and low voltage sensor cables, which have an inner (signal carrying) conductor and an outer (shield) conductor, have two insulators. One goes between the inner and outer conductor, and the other one over the outer conductor. Because of the way these signals behave, no other conductor can be used is place of the special radio antenna lead.
NOTE: Land Rover wires have color coded insulation for wire identification.
Wire Colour Chart
B - Black P - Purple
G - Green R - Red
K - Pink S - Grey
L - Light U - Blue
N - Brown W - White
O - Orange V - Yellow
WIRE GAUGE COMPARISON
Wire Gauge Size
Allowable voltage drop and current carrying capacity are the important factors in determining correct wire gauge or size.
The flow of current through a conductor can be compared to traffic on a super highway and on a one-lane street. The more lanes, the more traffic that can flow. A large conductor can carry a larger current than a smaller one of the same material. It offers less obstruction or "resistance" to the flow of electrons, due to its size. Conductor size is regulated by S.A.E. standards. This - system assigns "gauge" numbers to certain size wires.
Remember that the wire size increases as the American gauge number decreases. As an example, a sixteen gauge wire can carry less current than a twelve gauge wire. Metric sizes are larger for larger diameter wires.
WIRE SIZE CONVERSION TABLE
METRIC SIZES * AWG SIZES
.22 24
.35 22
.50 20
.80 18
1.00 16
2.00 14
3.00 12
5.00 10
8.00 18
13.00 6
19.00 4
32.00 2
* Denotes American Wire Gauge Systems
NOTE: If you are not sure of the wire size, start with the largest opening in your wire stripper and work down until you get a clean strip of the insulation. Be careful to avoid nicking or cutting any of the wires.
WIRE CURRENT CAPACITY
Conductors follow specific rules in respect to their ability to carry an electrical current.
1. Resistance increases as cross-sectional area decreases.
2. Resistance is directly related to the material from which the conductor is made. Silver conducts better than copper, but copper is better than aluminum.
3. Resistance goes up as the length of a conductor increases.
4. Resistance in most conductors goes up as the temperature of the conductor goes up.
5. Excessive current can heat a conductor to the point where the insulation will melt and the conductor will burn or melt.
The resistance of a uniform, circular copper wire is dependent upon the length of the wire, cross-sectional area of the wire, and the temperature of the wire. If the length is doubled, the resistance between the wire ends is doubled. If the cross-sectional area of a wire is doubled, the resistance for any given length will be cut in half.
An example of the effect of temperature on a section of wire is as follows:
A ten foot length of wire having a resistance of 0.03 ohm at .70 °F will have a resistance of 0.04 ohm at 185 °F, or an increase of thirty-five percent.
BODY WIRING
Solid Wires/Stranded Wires
Typical Body Wiring
Typical Printed Circuit
All automotive wiring falls into two categories: solid wires and stranded wires (made up of solid wires twisted or braided together). Solid wires will be found wherever current is low and where flexibility if not necessary. Stranded wires will be found where current flow is high or where flexibility is necessary due to component movement or vibration.
A good example of solid conductors can be found in the instrument panel "printed circuit." Here the solid conductors are simply flat metal pieces etched or imbedded onto a flat insulating plate. Like other conductors, the printed circuit conductors can be damaged by excessive current, flexing or damage to the insulation.
A good example of a stranded conductor is the accessory feed wires. These wires are required to carry all the current for the vehicle electrical systems. They also have to accommodate engine movement and vibration. Stranded conductors are the answer to both of these problems.
Soft copper is widely used for wire stranding. It is an excellent conductor, bends easily and solders readily. In addition to copper, stainless steel, carbon impregnated thread and elastomer type conductors are used for secondary ignition wire stranding. The carbon impregnated thread and elastomer type are designed to impart a controlled resistance in the secondary circuit.
PRIMARY WIRING/SECONDARY WIRING
The primary wiring handles the voltage produced by the vehicle's battery and charging system. It has sufficient insulation to prevent current loss at this voltage level. All wiring circuits in the car, with the exception of the ignition high tension circuit, use primary wire.
Secondary wire is used in the ignition system high tension circuit - coil to distributor, distributor to plugs. It has a heavy layer of insulation to afford protection against excessive loss of voltage to the surrounding air. This could impact sufficient current into an adjacent wire to cause it to fire a plug. This action is known as "cross-firing." Even with good insulation, it is important to arrange spark plug leads so that consecutively firing cylinders are separated.
SWITCHES
A switch is a mechanical device that is used to open and close an electrical circuit. A switch can be installed on the positive side (before the load) or on the ground side (after the load) of a circuit. A switch can be used to control the load device(s) directly or, in the case of higher current circuits, can be used to operate a relay which in turn operates the load device.
SOLENOIDS
A solenoid is an electromagnetic switching device that consists of a coil (electromagnet), moveable iron core (or plunger), and a return spring. One end of the plunger is attached to the switch, the return spring is also attached to the plunger. As current moves through the coil a magnetic field is developed which draws the plunger into its opening, closing the switch. When the current is stopped, the return spring moves the plunger and switch back to its original position. Solenoids are used in applications where very high amperage is required, as in the case of starter motors. Another type of solenoid is the electrovalve, which is used in automotive control systems to switch vacuum, air or fluids between various components.
RELAYS
A relay is an electromagnetic switching device that allows a low current circuit to operate a high current circuit. Relays allow smaller switches and wiring to be used in control circuits. The most common relays are the 4- or 5-pin type. The 4-pin relay has 1 output. The 5-pin relay has 2 outputs, an energized output and a relaxed or de-energized output. There are also specialized relays that may have diodes or resistors to control current flow.
RESISTORS
A resistor is an electrical component that slows current flow through a circuit. Resistors are used to drop voltage and amperage within an electrical circuit.
RESISTOR COLOR CODE
First & Second Color Band Third Color Band
Black 0 Black 0
Brown 1 Brown x10
Red 2 Red x100
Orange 3 Orange x1000
Yellow 4 Yellow x10,000
Green 5 Green x100,000
Blue 6 Blue x1,000,000
Violet 7 Silver x100
Gray 8 Gold x10
White 9
Fourth color band = Tolerance
Gold - 5% Silver - 10% None - 20%
SEMICONDUCTORS
Materials used in electrical circuitry differ greatly in their capacity to conduct electricity, ranging from good metallic conductors to the insulators. Between metallic conductors and insulators we have the semiconductors. They are named semiconductors because they do not conduct as well as conductors but as a rule conduct better than insulators.
Semiconductors which conduct free electrons are known as N-Type (N = negative). Semiconductors whose conductivity is based on "holes" are known as P-Type (P = positive). A "hole" represents a charge deficit of one electron. The electrons in this type of semiconductor are firmly bonded in the atom so therefore cannot contribute to electrical conduction. Since the "holes" are tightly surrounded by electrons, the vicinity has a negative charge. The "hole," therefore, has a positive charge.
Semiconductors play a very important role in automotive electronics. Without them it would not be possible to have alternators, ignition modules, electronically tuned radios, electronic fuel injection systems, etc. The four most common types of semiconductors used in automobiles are Diodes, Transistors, Integrated Circuits (Chips), and NTC (Negative Temperature Coefficient) Sensors.
DIODES
The diode is made up of two different semiconductor materials. Diodes are made of "P" and "N" type silicon. The material is arranged so that current can pass through it in one direction only.
The diode is a type of an electrical one-way check valve. It will allow one-half of the AC current sine wave to flow but blocks current flow in the 6ther direction. The direction the diode allows current to flow is referred to as forward bias; while the direction the diode blocks current flow is reverse bias. Because of this feature, the diode is ideally suited for use in AC generators (Alternators) to block a portion of the AC current being generated. A diode can be either positive or negative, depending on the direction of the forward bias. What determines the diode's polarity is whether the "P" or "N,' material is connected to the lead and the other connected to the case.
TRANSISTORS
The transistor is a three-element semiconductor device used among other things as a solid-state relay or switching device to control current flow. They are also equally used for amplifying voltage or current. The transistor is formed by layering the "P" and "N,' material. The elements or parts are the base, emitter, and the collector.
INTEGRATED CIRCUITS
Integrated Circuits or IC's are silicon chips or wafers. One chip is equivalent to hundreds of resistors, transistors, diodes, capacitors, and interconnecting circuits. The IC chip is the basic building block of modem electronic circuitry.
Through the use of IC chips, the size and power requirements of electronic components have been drastically reduced in size and cost.
IC's are used in the charging system's electronic voltage regulator, ignition electronic control unit, fuel injection electronic control unit, etc.
NTC (NEGATIVE TEMPERATURE COEFFICIENT) SENSORS
As previously discussed, the electrical resistance of metallic conductors increases as temperature rises. Non-metallic semiconductors on the other hand generally behave just the opposite. Their electrical resistance decreases as the temperature increases.
NTC Sensors are used in fuel injection systems and climate control systems, wherever accurate temperature input information is required.