For low-voltage integrators and installers, voltage drop is more than a classroom concept—it’s a daily design constraint that can make or break system performance. Undersized conductors and long cable runs can lead to cameras rebooting, mag locks losing holding force, speakers sounding weak, and LED fixtures dimming at the far end. Industry experts break down the physics behind voltage drop and highlight how the Windy City Wire Voltage Drop Calculator turns complex math into quick, confident decisions in the field.

What voltage drop is—and why it matters Every conductor has electrical resistance. As current flows through that resistance, some energy turns into heat, and the voltage available at the load drops. In simple terms:

• Ohm’s Law: V = I × R
• Voltage drop on a run: Vdrop = I × Rtotal
• Percent drop: %Drop = (Vdrop ÷ Vsupply) × 100

For two-conductor DC or low-frequency AC circuits typical of security, access control, AV, and lighting, the round-trip path must be included. If R is the resistance per foot of one conductor and L is the one-way distance, then Rtotal ≈ 2 × R × L.

Too much drop can cause brownouts, nuisance resets, reduced torque or holding force, and shortened equipment life. Many integrators design to a 3–5% drop target for sensitive electronics and up to 10% only when the device and standards allow. Always confirm allowable voltage ranges with the device manufacturer.

The physics behind the numbers Several physical variables determine voltage drop:

• Conductor material: Copper’s resistivity is lower than aluminum’s, which is why copper remains the preferred choice for low-voltage performance and consistency.
• Wire gauge (AWG): Larger conductors have more cross-sectional area and lower resistance. For example, typical DC resistance per 1000 ft for copper is about 10.15 Ω (20 AWG), 6.385 Ω (18 AWG), 4.016 Ω (16 AWG), 2.525 Ω (14 AWG), and 1.588 Ω (12 AWG).
• Length: Resistance increases linearly with length. Double the length and voltage drop roughly doubles for the same load.
• Current: Higher current draw produces a larger drop. Startup or inrush currents can momentarily increase drop even if steady-state looks acceptable.
• Temperature: Copper resistance rises with temperature. Hot ceiling plenums, attics, and outdoor runs can increase resistance and drop; a 20–30°C rise can add roughly 8–12% to resistance.
• Frequency and reactance: At 50/60 Hz and the distances typical in low-voltage work, capacitive and inductive effects are usually negligible, and skin effect is minimal. For most LV power circuits, DC resistance is the dominant factor.
• Construction: Stranded copper is slightly higher in resistance than solid of the same AWG but offers needed flexibility and durability for many LV applications. The difference is typically small relative to gauge and length choices.

A quick, real-world example Consider a 24 VDC camera drawing 0.6 A with a one-way run of 250 ft on 18 AWG copper.

• 18 AWG copper ≈ 6.385 Ω per 1000 ft
• Round-trip length = 500 ft
• Rtotal ≈ 6.385 × (500/1000) = 3.1925 Ω
• Vdrop = I × Rtotal = 0.6 × 3.1925 ≈ 1.92 V
• Percent drop ≈ 1.92/24 ≈ 8.0%
• Voltage at device ≈ 22.1 V

If the specification calls for less than 5% drop, stepping up to 14 AWG drops resistance to about 1.2625 Ω on the same run, reducing the voltage drop to roughly 0.76 V (≈3.2%), and delivering about 23.2 V to the camera. This is the sort of decision that integrators can make in seconds with the Windy City Wire Voltage Drop Calculator.

How Windy City Wire’s calculator simplifies the math Manual calculations can be time-consuming, especially when comparing multiple gauges, lengths, and loads across a project. The Windy City Wire Voltage Drop Calculator streamlines the process:

• Enter the supply voltage, load current or power, one-way cable length, and conductor gauge.
• Select copper conductor and circuit type commonly used in low-voltage applications.
• Instantly view voltage drop in volts and percent, and the estimated load voltage.
• Quickly iterate “what if” scenarios—try a heavier gauge, shorter run, or different current draw to meet a target percent drop.
• Identify the minimum recommended AWG that meets the design criteria.

The calculator helps integrators and distributors design with confidence, validate bids, and avoid costly callbacks caused by undervoltage at the device. Access the Windy City Wire Voltage Drop Calculator.

Where voltage drop shows up most in low-voltage systems

• Security cameras and surveillance: 12 VDC or 24 VDC power runs, as well as PoE where link length and cable category affect power available at the device.
• Access control: Mag locks, strikes, and controllers can be sensitive to undervoltage, especially during inrush.
• Fire and life safety: 24 VDC NAC and auxiliary power circuits require careful planning to meet device operating ranges and prevailing codes or listings.
• Pro AV and paging: Long 70V/100V speaker runs are designed to minimize current and drop, but branch lengths and load taps still matter.
• Lighting control and low-voltage LEDs: 12/24 V constant-voltage lighting is particularly susceptible to dimming on long runs.

Best practices to keep voltage drop under control

• Up-size the conductor: Moving from 18 AWG to 16 or 14 AWG often solves drop issues with minimal added cost compared to a service call.
• Shorten runs: Centralize or add remote power supplies to reduce one-way distance.
• Increase distribution voltage within spec: Supplying 24 VDC instead of 12 VDC (with proper device compatibility) halves the percent drop for the same current and wire.
• Distribute and regulate: Use regulated power supplies or local DC-DC converters to stabilize voltage at the device.
• Split loads: Avoid daisy-chaining too many devices on a single pair; run home runs or use power hubs to manage current.
• Plan for temperature: Expect higher resistance in hot spaces; design with margin.
• Verify terminations: Loose or corroded connections add resistance and create avoidable drop.
• Use true copper: Copper conductors deliver predictable resistance; avoid copper-clad aluminum for critical LV power.
• Consider PoE specifics: Match PoE class to load, respect maximum channel lengths, and use quality cable to minimize resistance per pair. Add midspans or extenders if needed.
• Leverage footage markings: Windy City Wire’s precise cable footage markings support accurate takeoffs and help avoid unplanned long runs that increase drop.

Why integrators choose Windy City Wire for voltage drop performance Windy City Wire manufactures high-quality copper low-voltage cables designed for consistent electrical performance and installer productivity. Accurate footage markings streamline planning and help teams right-size conductors to meet voltage targets. Smart wire management, durable jackets, and reliable, published electrical characteristics support repeatable field results. Beyond products, Windy City Wire backs integrators with practical tools and responsive technical support, including the Windy City Wire Voltage Drop Calculator to accelerate design decisions.

Start designing with confidence Voltage drop is governed by simple physics, but project constraints make optimization complex. The Windy City Wire Voltage Drop Calculator takes the guesswork out of sizing conductors, forecasting device voltage, and meeting performance targets. Integrators, installers, and distributors can visit windycitywire.com to launch the calculator and connect with Windy City Wire’s technical team for project-specific guidance.

Note: Always follow device specifications, applicable codes, and Authority Having Jurisdiction (AHJ) requirements when designing low-voltage power circuits.