When multiple electrical devices are connected to a power supply, the voltage available at the terminals often decreases. This phenomenon, known as voltage drop, occurs because the demands placed on the electrical system increase as more devices are turned on. Voltage, often described as electrical pressure, is the force that pushes electric charge through a circuit. The reduction in this pressure is a direct result of how electricity flows through real-world components.
Defining Electrical Load and Current
The concept of “load” in an electrical circuit refers to any component that consumes electrical power and converts it into another form, such as light, heat, or motion. When you turn on a device like a lamp or a motor, you increase the electrical load, which represents the demand for energy from the power source.
An increase in load directly corresponds to an increase in the flow of electric charge, measured as current (Amperes). Think of electricity like water flowing through a pipe; adding more appliances requires a greater volume of flow. When the load increases, the circuit must supply a higher current. This higher current is the key variable that initiates the voltage drop, as devices draw current based on their power requirements.
The Role of Internal Resistance
Every real-world power source, such as a battery or a generator, possesses a small, inherent opposition to current flow called internal resistance. This resistance is present within the source itself and the connecting wires, distinct from the resistance of the appliances being powered.
For a battery, internal resistance arises from the physical and chemical processes inside, such as the conductivity of the electrolyte and electrodes. For power lines, this resistance comes from the material and length of the conductor wires. Even the best conductors will slightly impede the flow of charge over distance. This internal resistance is a fixed property of the power supply and wiring. Since any current flowing out to the load must pass through it, it creates the conditions for energy loss.
The Mechanism of Voltage Drop
The mechanism of voltage drop is a direct consequence of the relationship between current and resistance. This interaction is described by a fundamental principle of electricity: the voltage that is lost internally is equal to the current multiplied by the internal resistance.
When the load increases, the current drawn from the source also increases. This greater current must travel through the fixed internal resistance of the power supply and wiring. The product of the increased current and the fixed internal resistance results in a larger amount of voltage being lost within the power system itself.
The voltage you measure at the device terminals is the original voltage supplied by the source minus this internally lost voltage. As the current draw goes up, the internal loss increases, which leaves less voltage available for the external load devices. This is why the terminal voltage drops when a high-demand appliance is switched on.
Practical Implications and Mitigation
The result of voltage drop can manifest in several noticeable ways in a home or industrial setting. Devices that rely on a consistent voltage for proper operation may suffer reduced performance. For example, incandescent lights may dim noticeably, and electric motors may run slower or struggle to start effectively.
In electronic systems, a voltage drop can lead to malfunctions or unreliable operation, as components may not receive the precise voltage levels they require. Furthermore, the energy lost due to internal resistance is dissipated as heat, which can lead to overheating in the power source or wiring, raising safety concerns.
To manage and minimize voltage drop, engineers and electricians employ several strategies focused on reducing the total resistance in the delivery path.
Increasing Conductor Size
One common solution is to increase the size of the conductors, using thicker wires, which have a naturally lower resistance. Lower-gauge wiring indicates a thicker diameter and therefore less resistance over the same length.
Reducing Conductor Length
Another approach is to reduce the length of the conductor path, as resistance is directly proportional to the wire’s length.
Designing for Lower Internal Resistance
Power supplies can also be designed with lower inherent internal resistance, often referred to as lower source impedance, to better maintain voltage stability under heavy load. By addressing resistance, the voltage loss for any given current draw can be controlled and kept within acceptable operational limits.