Understanding Voltage Drop and Its Impact on Electrical Circuits

When electrical current flows through a wire, it is pushed by electrical potential, also known as voltage. However, the wire itself presents a contrary pressure that the current must overcome. The loss of electrical potential due to this pressure is called voltage drop. For alternating current (AC), this contrary pressure is known as impedance, which is a vector quantity consisting of resistance and reactance (the reaction of a built-up electric field to changes in current). For direct current (DC), the contrary pressure is referred to as resistance.

At Monday Tools, we understand the importance of controlling voltage drop to ensure the reliable performance of electrical systems. Excessive voltage drop can lead to flickering or dim lights, underperforming heaters, and overheated motors, which may eventually fail. To prevent these issues, it is recommended that voltage drop remain below 5% under fully loaded conditions. This can be achieved by selecting the right wire and properly managing extension cords and other devices.

Major Causes of Voltage Drop

1. Wire Material

The material of the wire significantly impacts voltage drop. Metals such as silver, copper, gold, and aluminum have excellent electrical conductivity. Copper and aluminum are the most commonly used materials due to their affordability compared to silver and gold. Copper, being a better conductor than aluminum, exhibits less voltage drop for a given wire size and length.

2. Wire Size

Wire size also plays a critical role. Larger wires (with a greater diameter) have less voltage drop than smaller ones of the same length. In the American Wire Gauge (AWG) system, a 6-gauge decrease doubles the wire diameter, and a 3-gauge decrease doubles the wire’s cross-sectional area. Similarly, in the Metric Gauge scale, the gauge is 10 times the diameter in millimeters. For example, a 50-gauge metric wire would have a diameter of 5 mm.

3. Wire Length

Voltage drop increases with wire length. Shorter wires have less voltage drop compared to longer ones for the same wire size. While voltage drop may not pose an issue in typical household circuits, it becomes critical for long-distance runs, such as wiring for outbuildings or well pumps.

4. Current Flow

The amount of current flowing through a wire impacts voltage drop. An increase in current results in higher voltage drop levels. The ampacity (short for ampere capacity) of a wire is the maximum amount of current it can safely carry. Ampacity depends on factors such as the material of the wire, the speed of AC alternation, and the operating temperature.

Bundling Cables

When cables are bundled together, the heat they generate collectively affects their ampacity and can increase voltage drop. For this reason, strict guidelines for bundling cables must be followed to ensure safety and performance.

Cable Selection: Key Principles

At Monday Tools, we emphasize two critical principles when selecting cables:

1. Current Carrying Capacity: The cable must carry the current load without overheating, even under extreme temperatures.
2. Sound Earthing: The cable should ensure safety by (i) limiting the voltage to which people are exposed to a safe level and (ii) enabling fault currents to trip fuses promptly.

Calculating Voltage Drop

Voltage drop can be calculated using Ohm’s Law, which is fundamental for understanding electrical circuits:

Vdrop=I⋅R\text{Vdrop} = I \cdot RVdrop=I⋅R

Where:

• I: Current through the wire (in amperes)
• R: Resistance of the wire (in ohms)

Resistance is often measured as length-specific resistance in units of ohms per kilometer or ohms per 1,000 feet. Since wires are round-tripped (current flows to the load and back), the formula for a single-phase or direct current circuit is:

Vdrop=2⋅I⋅R⋅L\text{Vdrop} = 2 \cdot I \cdot R \cdot LVdrop=2⋅I⋅R⋅L

For a three-phase circuit, the formula is:

Vdrop=3⋅I⋅R⋅L\text{Vdrop} = \sqrt{3} \cdot I \cdot R \cdot LVdrop=3⋅I⋅R⋅L

Where:

• I: Current through the wire
• R: Length-specific resistance
• L: One-way wire length

Typical AWG Wire Sizes

The American Wire Gauge (AWG) system is widely used in North America to standardize the diameters of round, solid, non-ferrous, electrically conducting wire. Below are some typical wire sizes used for different applications. At Monday Tools, we offer high-quality wires in a variety of AWG sizes to meet your electrical needs.

By understanding voltage drop and selecting the appropriate materials, wire sizes, and configurations, you can ensure safe and efficient electrical systems. For reliable tools and materials to support your projects, trust Monday Tools!