Resistance between the voltage source and the load causes a voltage drop in wiring. A poor connection, corrosion, the type of wire being used, the diameter or gauge of the wire, and the distance between the source and the load can all cause resistance in wiring.
Voltage drop in an electrical system can cause problems that prevent circuits from working properly. Voltage drops along a ground path in an electrical system can cause the entire system to experience problems. Excessive voltage drop could damage electronic components and may pose a safety or fire risk as well. According to the National Electrical Code, the largest acceptable voltage drop between a voltage source and the furthest load is 5%. Voltage drops greater than this require diagnosis and repair as soon as possible.