Voltage drop is the reduction of supply voltage in an electrical circuit due to resistance. It occurs across components and wiring, and must be calculated for sensitive applications. A voltage drop formula can be used to accurately calculate the drop.
Voltage drop is a term used to describe any reduction in supply voltage in a complete electrical circuit. The term can be used to describe a voltage drop across a specific component in the circuit, the measured voltage drop across the entire circuit, or as a broad description of the phenomenon of voltage drop in a circuit in general. All electrical circuits, however simple, have some resistance to the flow of electric current through them. This resistance causes the electric current to work harder and therefore absorb energy. This expenditure of energy is what causes the voltage reduction described by the term voltage drop.
For example, a simple circuit might consist of a 9-volt battery connected to a simple flash bulb with a small switch. If you were to measure the voltage across the battery terminals with the switch open, the multimeter reading would be approximately 9 volts. If you closed the switch and lit the bulb, that reading would decrease by about 1.5 volts. This voltage drop is what is known as a voltage drop and occurs as a result of the work the battery has to do to light up the bulb. Each component in a circuit, including wiring, offers some resistance to the flow of electric current and causes an associated voltage drop.
In applications that are extremely sensitive to the supply voltage, such as electronic devices, these voltage losses must be carefully calculated and the supply voltage must be adjusted to take them into account. A 12 volt direct current (DC) power supply, for example, will typically produce an output of 13.8 volts to accommodate this voltage drop phenomenon. In applications that require very long cables, it is common practice to use fairly heavy cables that have less resistance to the flow of electric current in an attempt to minimize the effects of voltage losses. The total potential voltage loss in any circuit must therefore be carefully calculated during the design and specification stage of a project to ensure that the final result meets all requirements.
Any voltage drop in a circuit can, fortunately, be calculated with great accuracy using a voltage drop formula. This allows for consistent and predictable results at the end of an installation. These calculations will differ based on the type of circuit, voltage supply and component involved and can be extremely complex, often requiring the use of a voltage drop calculator. However, they do require the guess work of fine-tuning the power supply specifications to match the resistance of the circuit.
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