Understanding Wire Gauges: AWG, Amperage, Diameter, and Resistance

Wire gauge plays a critical role in data centers, where reliable power distribution is essential for maintaining uptime and efficiency. Selecting the right American Wire Gauge (AWG) ensures that circuits handle the required current without overheating, excessive voltage drop, or energy loss.

In this article, we’ll explain how AWG affects current capacity, resistance, voltage drop, and overall performance in data center power distribution.

What Is AWG?

AWG, or American Wire Gauge, is a numerical system that defines the thickness of electrical wires. The numbers may seem counterintuitive:

• Smaller AWG numbers represent thicker wires, which carry more current.
• Larger AWG numbers indicate thinner wires, which have higher resistance and lower current capacity.

For example, a 10 AWG wire has a diameter of 2.588 mm and carries 30A, while a 20 AWG wire is much thinner at 0.812 mm and only supports 5A.

The relationship between AWG and wire size is inverse: as the gauge number increases, the wire diameter decreases.

How Wire Gauge Affects Power Distribution

Current-Carrying Capacity (Ampacity)

Data centers in the United States commonly use circuits with voltages of 120V or 208V, with currents ranging from 15A to 50A. The thicker the wire, the more current it can carry safely. If a wire is too thin for the current load, it will overheat and create a fire hazard.

Resistance and Energy Loss

Resistance increases as the wire gets thinner. Higher resistance means greater voltage drop, reduced efficiency, and potential power issues for IT equipment.

For example:

• 10 AWG wire has a resistance of 1 milliohm per foot
• 20 AWG wire has 10 milliohms per foot

A 20 AWG wire is 10 times more resistive than a 10 AWG wire of the same length, leading to significant voltage drop over long runs.

Voltage Drop Considerations

Voltage drop occurs when electrical resistance causes a reduction in voltage as power flows through the wire. While minor voltage drops are normal, excessive drops can cause power supply failures, performance issues, and unexpected shutdowns in servers and network equipment.

To minimize voltage drop, the National Electrical Code (NEC) recommends keeping it under 3% for branch circuits. The formula for estimating voltage drop is:

Vdrop= 2 × R × L × I /1000

Where:

• R = Wire resistance per 1,000 feet (ohms)
• L = One-way cable length (feet)
• I = Current (amps)

For example, in a 208V 30A circuit using 10 AWG wire over 100 feet:

• Resistance of 10 AWG = 1.24 ohms per 1,000 feet
• Current = 30A
• Distance = 100 feet

Vdrop= 2 × 1.24 × 100 × 30 /1000 = 7.44V

This results in a 3.6% voltage drop, which is slightly above the recommended limit. Upgrading to an 8 AWG wire would reduce resistance and improve efficiency.

Recommended Wire Gauges for Data Center Circuits

Choosing the right wire size depends on circuit amperage, voltage, and cable length. The table below provides minimum wire gauge recommendations for standard data center circuits (assuming short cable runs):

For longer cable runs, thicker wires are necessary to reduce voltage drop.

Calculating Wire Diameter Using AWG

If you need to determine wire diameter from the AWG number, use the formula:

d_n= 0.127 × 92 ⁽³⁶⁻ⁿ⁾ /39

Where:

• d_n is the wire diameter in millimeters
• n is the AWG number

For example, calculating the diameter of a 20 AWG wire:

d₂₀= 0.127 × 92 ^(36−20) /39

Using a calculator, this gives:

d₂₀ ≈ 0.812 mm

This matches standard wire gauge charts and confirms the accuracy of the formula.

Why Wire Gauge Matters in Data Centers

Prevents Overheating and Fire Hazards

Using undersized wires increases heat buildup, leading to potential fire risks. Proper wire sizing keeps temperatures within safe limits.

Reduces Power Loss and Voltage Drop

Every watt lost due to resistance turns into heat, reducing efficiency. Thicker wires lower resistance and minimize energy waste.

Ensures Stable Power for IT Equipment

Servers, switches, and storage arrays need consistent voltage to operate reliably. Voltage drop beyond recommended levels can cause malfunctions and downtime.

Meets Electrical Code Compliance

The NEC and local regulations dictate minimum wire sizes for safety. Undersized wires violate electrical codes and increase liability risks.

Choosing the Right Wire Gauge for Your Data Center

To select the right wire size, consider:

• Circuit amperage – Higher currents require thicker wires.
• Cable length – Long runs need lower resistance to prevent voltage drop.
• Future expansion – Choosing slightly thicker wires now can support higher loads later.
• Compliance requirements – Follow NEC and local codes to ensure safety and reliability.

Understanding Wire Gauges – Final Thoughts

Wire gauge plays a critical role in data center power distribution. Smaller AWG numbers mean thicker wires, which carry more current with less resistance.

For 120V circuits, 12-14 AWG is common, while 208V circuits require 10-6 AWG depending on amperage. Longer distances may require thicker wires to maintain efficiency.

By selecting the correct wire gauge, you maximize power efficiency, equipment reliability, and long-term infrastructure stability in your data center.