Voltage Calculator Drop

Voltage Drop Calculator

Use this calculator to determine the voltage drop in an electrical circuit based on current, length, wire gauge, and conductor material. Understanding voltage drop is crucial for electrical system efficiency and safety.

DC / Single-Phase AC Three-Phase AC

Copper Aluminum





14 AWG (4110 CM) 12 AWG (6530 CM) 10 AWG (10380 CM) 8 AWG (16510 CM) 6 AWG (26240 CM) 4 AWG (41740 CM) 2 AWG (66360 CM) 1 AWG (83690 CM) 1/0 AWG (105600 CM) 2/0 AWG (133100 CM) 3/0 AWG (167800 CM) 4/0 AWG (211600 CM)

Warning:

Note:

Calculation Results:

Calculated Voltage Drop:

Percentage Voltage Drop:

Remaining Voltage at Load:

Understanding Voltage Drop in Electrical Circuits

Voltage drop is a fundamental concept in electrical engineering and a critical consideration for anyone designing or installing electrical systems. It refers to the reduction in electrical potential (voltage) along the length of a conductor through which current is flowing. This reduction occurs because all conductors have some electrical resistance, and as current passes through this resistance, some electrical energy is converted into heat, resulting in a loss of voltage.

Why is Voltage Drop Important?

Excessive voltage drop can lead to several undesirable consequences:

• Reduced Efficiency: Lost voltage means lost power, which translates to wasted energy and higher electricity bills.
• Equipment Malfunction: Many electrical devices are designed to operate within a specific voltage range. If the voltage supplied to them drops too low, they may not function correctly, leading to erratic behavior, reduced performance, or even premature failure. Motors, for example, can overheat and burn out if operated at significantly reduced voltage.
• Safety Hazards: While less common, extreme voltage drop can sometimes be associated with overheating wires if the wire gauge is too small for the current, posing a fire risk.
• Dim Lighting: In lighting circuits, noticeable voltage drop can cause lights to appear dim or flicker.

Factors Affecting Voltage Drop

The amount of voltage drop in a circuit is influenced by four primary factors:

1. Current (Amperes): The higher the current flowing through a conductor, the greater the voltage drop. This is a direct relationship (Ohm's Law: V = I * R).
2. Length of the Conductor (Feet): The longer the wire, the more resistance it presents to the current, and thus, the greater the voltage drop.
3. Wire Gauge (Size): Thicker wires (smaller AWG numbers) have lower resistance per unit length than thinner wires (larger AWG numbers). Using a larger wire gauge reduces voltage drop.
4. Conductor Material: Different materials have different inherent resistivities. Copper is a better conductor than aluminum, meaning it has lower resistivity and will exhibit less voltage drop for the same size and length.

The Voltage Drop Formula

The calculator above uses a common formula for calculating voltage drop, which varies slightly for DC/single-phase AC versus three-phase AC systems:

For DC or Single-Phase AC Circuits:

VD = (2 * K * I * L) / CMA

For Three-Phase AC Circuits:

VD = (√3 * K * I * L) / CMA

Where:

• VD = Voltage Drop (Volts)
• K = Resistivity of the conductor material (Ohms per circular mil foot).
  • For Copper (at 75°C): Approximately 12.9
  • For Aluminum (at 75°C): Approximately 21.2
• I = Current (Amperes)
• L = One-way length of the circuit (Feet)
• CMA = Circular Mils Area of the conductor (determined by wire gauge)
• 2 = Multiplier for DC/single-phase to account for the current traveling to and from the load.
• √3 (approximately 1.732) = Multiplier for three-phase AC circuits.

National Electrical Code (NEC) Recommendations

The National Electrical Code (NEC) does not mandate specific voltage drop limits, but it does provide recommendations in Annex D, Example D1. It suggests that for efficiency, feeders and branch circuits should be sized so that the voltage drop does not exceed 3% at the farthest outlet of power, heating, and lighting loads. The total voltage drop for both feeders and branch circuits combined should not exceed 5%.

Example Calculation

Let's consider a common scenario:

• System Type: Single-Phase AC
• Conductor Material: Copper
• Current: 15 Amperes
• Circuit Length (one-way): 100 Feet
• Wire Gauge: 14 AWG (CMA = 4110)
• Source Voltage: 120 Volts

Using the formula: VD = (2 * 12.9 * 15 * 100) / 4110 = 9.40 Volts

Percentage Voltage Drop: (9.40 / 120) * 100 = 7.83%

In this example, a 7.83% voltage drop is significantly higher than the recommended 3% by the NEC. This could lead to dim lights, inefficient appliance operation, and potential damage to sensitive electronics.

To mitigate this, one might consider:

• Using a larger wire gauge: If we change to 10 AWG copper (CMA = 10380) for the same circuit:
  VD = (2 * 12.9 * 15 * 100) / 10380 = 3.73 Volts
  Percentage Voltage Drop: (3.73 / 120) * 100 = 3.11%
  This is much better, closer to the 3% recommendation.
• Reducing the circuit length: If feasible, shortening the wire run.
• Increasing the source voltage: Not always practical for existing systems, but higher voltage systems inherently experience lower percentage voltage drop for the same power delivery.

Conclusion

Properly calculating and managing voltage drop is essential for ensuring the reliability, efficiency, and safety of any electrical installation. Always aim to keep voltage drop within acceptable limits, typically below 3% for branch circuits, to ensure optimal performance of your electrical equipment.