Technician Handbook 623 Electrical Circuit Diagnosis Resistance Factors Length – A longer wire has more resistance than a shorter one. Diameter – A small gauge wire has more resistance than a larger gauge wire. • Wire diameters are rated by gauge • Gauges 1, 2, 3 are thicker with less resistance and more current capacity • Gauges 18, 20, 22 are thinner with more resistance and less current capacity Temperature – Changes in temperature affect resistance differently in different materials. • For most conductors, resistance increases as the temperature increases. For example, the resistance of a lamp’s filament increases as it heats up.
• Insulators, on the other hand, have less resistance at higher temperatures. • Certain semiconductor devices called thermistors exhibit decreasing resistance as temperature increases. Condition – The condition of a wire or connector can increase resistance. • A nicked wire or a wire with broken wire strands has higher resistance than an undamaged wire because the wire’s diameter is effectively diminished. • Corrosion can increase resistance because the conducting material is replaced by higher-resistance corrosion by-products. • Loose connections are like wires with broken wire strands. Fewer contact points between the connecting components result in higher resistance.
HINT When replacing a wire in a circuit, do not use a thinner wire or a longer wire because this will increase the resistance in the circuit. 12 Technical Training