Voltage Drop Calculator & Wire Size Guide — Formula, AWG Chart, and DC Wiring

What Is Voltage Drop?

Voltage drop is the loss of electrical potential that occurs as current flows through a wire. Every wire has resistance, and that resistance converts some of the electrical energy into heat before it reaches the device at the other end. The longer the wire and the thinner it is, the more voltage is lost along the way.

Think of it like water pressure in a garden hose. If you connect a short hose to the tap, the water sprays out at full pressure. But if you connect a 200-foot hose, the friction inside the hose reduces the pressure at the end — you get a weak trickle instead of a strong spray. Voltage drop works the same way: the wire is the hose, the current is the water, and the resistance of the wire is the friction.

In household 120V AC wiring, voltage drop is rarely noticeable because even a 3% drop (3.6V) leaves 116.4V — more than enough for any appliance. But in low-voltage DC systems like 12V actuators, solar panels, LED lighting, marine electronics, and RV wiring, a 3% drop is only 0.36V, and even a 5% drop (0.6V) can cause motors to run noticeably slower, LEDs to dim, sensors to malfunction, and control systems to behave erratically.

This guide covers voltage drop from first principles through practical application, with three interactive calculators: a universal voltage drop calculator for any DC or AC circuit, a wire size calculator that tells you the minimum AWG gauge for your application, and an actuator-specific calculator that factors in load, feedback sensors, and the real-world effects on actuator performance.

Why Voltage Drop Matters in Low-Voltage Systems

Voltage drop is a universal electrical phenomenon, but it becomes critically important in low-voltage DC systems for a simple mathematical reason: the percentage of voltage lost is much higher at 12V than at 120V for the same wire and current.

Consider this comparison: a circuit draws 5 amps through 25 feet of 18 AWG copper wire (one-way distance, 50 feet total round trip). The wire resistance is approximately 6.385 Ω per 1000 feet, so the total resistance is 0.319 Ω, giving a voltage drop of 1.60V.

The same 1.60V drop is invisible at 120V but devastating at 12V. This is why low-voltage DC systems — actuators, marine electronics, solar installations, RV wiring, automotive accessories, LED lighting, and CCTV cameras — require much more careful wire sizing than household wiring.

Applications where voltage drop causes the most problems include: linear actuators on long cable runs (boat hatches, solar trackers, gate openers), dual actuator setups with unequal wire lengths, feedback actuators where sensor signals degrade over distance, and any 12V or 24V installation where wires run more than 10 feet from the power supply.

Voltage Drop Formula

The formula for DC voltage drop is derived directly from Ohm's Law (V = I × R):

Where:

• V_drop = voltage drop in volts
• L = one-way wire length (source to load) in meters
• I = current in amps
• ρ = resistivity of the conductor material (Ω·m). Copper = 1.724 × 10⁻⁸, Aluminum = 2.655 × 10⁻⁸
• A = cross-sectional area of the wire in m²

The factor of 2 accounts for the complete circuit — current flows from the supply to the load on the positive wire and returns on the negative wire, so the total wire length is twice the one-way distance.

Using resistance per unit length (from an AWG chart) simplifies the formula:

Where R_{per ft} is the resistance per foot of the wire gauge from the AWG reference table below.

The percentage voltage drop is:

The NEC recommends keeping total voltage drop below 5% for the complete circuit (feeder + branch), and below 3% for branch circuits alone. For 12V DC actuator systems, FIRGELLI recommends a maximum of 3% for standard actuators and 2% for feedback actuators with position sensors.

For three-phase AC systems, the formula uses √3 instead of 2:

Voltage Drop Calculator (Universal DC/AC)

Enter your circuit parameters to calculate the voltage drop and percentage loss. This calculator works for any DC or single-phase AC circuit — actuators, LED lighting, solar, marine, automotive, CCTV, or household wiring.

Wire Size Calculator (Find the Right AWG)

Don't know what wire gauge to use? Enter your voltage, current, distance, and maximum allowable voltage drop, and this calculator will tell you the minimum wire gauge required.

Actuator Wiring Calculator

This calculator is designed specifically for linear actuator installations. Select your actuator type, enter the wire length and load conditions, and it will tell you whether your wiring is adequate — including warnings for feedback sensor voltage drop.

AWG Wire Gauge Reference Table

This table shows the key properties of copper wire from 0000 (4/0) AWG through 26 AWG. The resistance values are at 20°C (68°F). For aluminum wire, multiply the resistance by 1.54.

For a more detailed AWG reference including temperature derating, insulation types, and conversion between metric and American gauges, see our complete AWG Wire Gauge Chart and Guide.

Why Your Actuator Is Running Slow

This is one of the most common questions FIRGELLI’s support team receives: “My actuator is running slower than the speed listed on the spec sheet. Is it defective?”

Almost always, the answer is no — it is voltage drop.

A linear actuator’s speed is directly proportional to the voltage it receives. If the spec sheet says an actuator moves at 0.5 inches per second at 12V, and it only receives 10.5V because of voltage drop in the wiring, it will move at roughly 0.44 inches per second — 12% slower. This is not a defect; it is basic physics.

Here is a real-world example: a customer installs a 12V Classic Linear Actuator to open a boat hatch. The actuator is 20 feet from the battery, and the customer used the 18 AWG wire that came with the project. The actuator draws 5A under load.

The actuator receives 10.72V instead of 12V, so it runs about 10% slower and produces less force. Under heavy load, the current draw increases, the voltage drop gets worse, and the actuator may stall entirely. During startup, surge current (typically 1.5-2x running current) causes an even larger momentary voltage dip that can make the actuator hesitate or fail to start.

The solution is straightforward: use 14 AWG wire instead of 18 AWG. The voltage drop drops from 1.28V to 0.51V (4.2%), and the actuator receives 11.49V — close enough to full speed. For critical applications, 12 AWG wire brings the drop down to 0.32V (2.6%), well within the recommended 3% limit.

Use the Actuator Wiring Calculator above to check your specific setup before running wire.

Why Two Actuators Run at Different Speeds

Another common scenario: a customer installs two actuators to raise a heavy lid, platform, or solar panel — and one side moves faster than the other, causing the load to tilt or bind.

If both actuators are the same model and have the same load, the most likely cause is unequal wire lengths. When one actuator is 10 feet from the power supply and the other is 25 feet away, the longer wire has more resistance and more voltage drop. The close actuator might receive 11.8V while the far one receives only 11.1V — a difference of 0.7V is enough to create a visible speed mismatch.

The problem compounds under load because both actuators share the same supply wire for part of the run. When both are drawing current simultaneously, the shared portion of the wire carries double the current, increasing the voltage drop on that shared segment. The actuator at the end of a daisy-chain configuration gets hit the hardest.

There are several ways to fix this:

• Use equal wire lengths for both actuators, even if it means running extra wire to the closer one. This is the simplest solution.
• Run dedicated wire pairs from the power supply to each actuator (star topology) instead of daisy-chaining one actuator off the other.
• Use thicker wire on the longer run to equalize the voltage at each actuator.
• Use a synchronization controller that actively adjusts motor power to keep both actuators moving at the same speed regardless of voltage differences.

Feedback Sensor Problems from Voltage Drop

Feedback actuators use a sensor — typically a Hall effect sensor, optical encoder, or potentiometer — to report the actuator’s position back to the controller. These sensors operate on a 5V signal line, and their output voltage is proportional to the actuator’s position.

Here is the problem: if the 5V supply to the sensor drops because of resistance in the wire, the sensor’s output changes even though the actuator has not moved. A controller that expects 0-5V from the sensor might instead receive 0-4.3V, causing it to misinterpret the position. The actuator may overshoot its target, undershoot, oscillate back and forth, or report incorrect positions to the system.

This is subtle and hard to diagnose because the motor itself seems to work fine — it extends and retracts normally. But the position feedback is wrong, which causes the control system to behave erratically. Customers often think the actuator or controller is faulty when the real culprit is the wire.

The sensor draws very little current (typically 10-20mA), so you might assume voltage drop would be negligible. But the 5V signal line is often routed through the same cable as the motor power wires (12V), and if that cable uses thin wire over a long run, even the small sensor current can see meaningful drop. More importantly, electrical noise from the motor switching on and off can inject spikes into the signal line that corrupt the sensor reading.

Best practices for feedback actuator wiring:

• Run a dedicated wire pair for the 5V sensor signal, separate from the motor power wires. 22-24 AWG is sufficient for the low sensor current.
• Use shielded cable or twisted pair for the signal wires to reject motor noise.
• Keep the 5V signal wire drop below 2% (0.1V) for reliable position readings.
• If the wire run exceeds 30 feet, consider mounting the controller closer to the actuator rather than at the power supply end.
• Avoid daisy-chaining the 5V signal between multiple feedback actuators — each should have its own signal pair back to the controller.

Use the Actuator Wiring Calculator above with the feedback option enabled to check whether your signal line is adequate.

How to Reduce Voltage Drop

There are four fundamental ways to reduce voltage drop in any circuit. Listed from most effective to least:

1. Use thicker wire. This is the most direct solution. Going from 18 AWG to 14 AWG reduces wire resistance by about 60%. Going to 12 AWG reduces it by 75%. The tradeoff is cost and bulk — thicker wire costs more and is harder to route through tight spaces. But for long runs, the cost of thicker wire is almost always justified by the improvement in performance.

2. Shorten the wire run. Voltage drop is directly proportional to length. Halving the wire distance halves the drop. If possible, mount the power supply or controller closer to the actuator. In marine and RV applications, this often means mounting a dedicated battery or DC-DC converter near the device rather than running long cables back to the main battery bank.

3. Increase the supply voltage. Moving from a 12V system to a 24V system cuts the required current in half for the same power output (Power = Voltage × Current). Since voltage drop depends on current, halving the current reduces the voltage drop by half — and the percentage drop improves even more because the higher supply voltage gives you more headroom. This is why industrial and commercial actuator systems often use 24V or 48V.

4. Run dedicated wires for each device. Instead of daisy-chaining multiple actuators or devices on a single wire pair, run a separate wire pair from the power supply to each device (star topology). This prevents one device’s current draw from increasing the voltage drop seen by another device.

12V vs 24V: Why Higher Voltage Means Less Drop

A 12V actuator rated at 60W draws 5A (Power ÷ Voltage = 60W ÷ 12V = 5A). A 24V actuator with the same 60W rating draws only 2.5A. Since voltage drop is proportional to current, the 24V actuator creates only half the voltage drop in the same wire.

But it gets even better. The percentage drop is also calculated against a higher base voltage, so the same absolute drop represents a smaller percentage:

The 12V system has an unacceptable 8.4% voltage drop and needs a wire upgrade. The 24V system is comfortably within the 3% limit using the same wire. This is why FIRGELLI offers most actuator models in both 12V and 24V versions, and why 24V is recommended for any installation where wires run more than 15 feet.

Voltage Drop vs Ampacity

Wire sizing is governed by two independent limits: voltage drop and ampacity. Many people confuse them or only check one.

Ampacity is the maximum current a wire can carry before it overheats to the point where the insulation degrades, potentially causing a fire. This is a safety limit — exceeding it is dangerous. Ampacity depends on the wire gauge, insulation type, ambient temperature, and how the wire is bundled with other conductors.

Voltage drop is the performance limit — it determines whether your device gets enough voltage to operate correctly. Exceeding the voltage drop limit is not immediately dangerous (the wire won’t catch fire), but your device will underperform.

In high-voltage systems (120V AC and above), ampacity is usually the limiting factor. You size the wire for safety, and voltage drop takes care of itself. But in low-voltage DC systems (12V, 24V), the relationship reverses: you will almost always need to upsize the wire for voltage drop long before ampacity becomes a concern.

For example, 18 AWG copper wire has an ampacity of 7A — more than enough for a 5A actuator from a safety perspective. But over a 20-foot run at 12V, the voltage drop with 5A is 10.6%, which is far too high. You need at least 14 AWG wire to get the voltage drop below 3%, even though 18 AWG is perfectly safe from a fire standpoint.

Always check both limits. Size for voltage drop first (using the calculators above), then verify that the chosen wire also meets the ampacity requirement for your current.

Worked Examples

Example 1: Solar Tracker Actuator (Long Run)

A 12V Super Duty Actuator drives a solar panel tracker. The actuator draws 8A under full load and is 40 feet from the battery bank. Wire is 16 AWG copper.

Example 2: Dual Actuators on a Boat Hatch

Two 12V Classic Actuators (5A each) lift a boat hatch. Actuator A is 8 feet from the battery; Actuator B is 18 feet away. Both use 16 AWG wire. A shared 16 AWG trunk runs 6 feet from the battery to a junction box, then individual runs go to each actuator.

Example 3: Feedback Actuator with Long Signal Run

A 12V Feedback Actuator with a Hall effect sensor is mounted 30 feet from the Arduino controller. The motor power wires are 14 AWG (adequate for the 5A motor draw). The 5V sensor wires use 22 AWG, bundled in the same cable.

Related Guides and Calculators

Frequently Asked Questions

What is voltage drop?

Voltage drop is the loss of electrical potential (voltage) that occurs as current flows through a wire. Every wire has resistance, and that resistance converts some of the electrical energy into heat. The longer the wire and the thinner it is, the more voltage is lost before it reaches the device at the other end. In a 12V DC system, even a small drop of 1–2 volts can significantly affect device performance.

How do you calculate voltage drop in a DC circuit?

Use the formula: Voltage Drop = (2 × Length × Current × Resistivity) ÷ Wire Cross-Sectional Area. The factor of 2 accounts for the return wire (positive and negative). For copper wire at room temperature, resistivity is 1.724 × 10⁻⁸ Ω·m. You can also use the simplified version: V_drop = 2 × L × I × R, where R is the resistance per unit length from an AWG chart.

What is the maximum acceptable voltage drop?

The NEC recommends no more than 3% for branch circuits and 5% total for the complete system. For 12V DC actuator systems, FIRGELLI recommends keeping voltage drop below 3% (0.36V) for standard actuators and below 2% (0.24V) for actuators with feedback sensors. At 24V DC, you have more headroom — 3% is 0.72V.

Why is my linear actuator running slower than expected?

The most common cause is voltage drop over long wire runs. A 12V actuator drawing 5A through 20 feet of 18 AWG wire loses about 1.28V — the motor only receives 10.72V instead of 12V. Since actuator speed is directly proportional to voltage, the actuator runs roughly 10% slower. The solution is to use a thicker wire gauge or shorten the cable run. Use our Actuator Wiring Calculator to check your setup.

Why does one of my two actuators run slower than the other?

When two actuators share a power supply but have different wire lengths, the actuator with the longer cable run receives less voltage due to greater voltage drop. Even a difference of 10 feet can cause noticeable speed mismatch. The fix is to use equal wire lengths for both actuators, or use thicker wire on the longer run to equalize the voltage at each actuator. A synchronization controller can also solve this electronically.

Why is my feedback actuator giving incorrect position readings?

Feedback actuators use a 5V signal line for Hall effect or optical sensors. If the 5V supply voltage drops due to long wire runs or shared power lines, the sensor output voltage changes even though the actuator position has not. This causes the controller to read incorrect positions. The solution is to run a dedicated, appropriately sized wire pair for the 5V signal line, separate from the motor power wires.

What wire size do I need for a 12V linear actuator?

It depends on the current draw and wire length. For most 12V actuators drawing 5A or less over runs under 15 feet, 16 AWG wire is sufficient. For longer runs (15–30 feet) or higher-current actuators, 14 AWG or 12 AWG is recommended. Use our Wire Size Calculator to find the exact gauge — enter your actuator’s current draw, the one-way wire length, and aim for less than 3% voltage drop.

Does wire length affect voltage drop?

Yes — voltage drop is directly proportional to wire length. Doubling the wire length doubles the voltage drop for the same current and wire gauge. This is why voltage drop is rarely an issue in short household wiring but becomes critical in long runs to outbuildings, boats, RVs, solar installations, and remote actuator installations.

Is voltage drop worse in 12V systems than 120V systems?

Yes, significantly. A 3% voltage drop at 120V AC is 3.6 volts — the device barely notices. A 3% drop at 12V DC is only 0.36 volts. Since DC motors and actuators are sensitive to even small voltage changes, the same wire that works fine at 120V can cause serious performance issues at 12V. Low-voltage DC systems always need thicker wire or shorter runs than equivalent AC systems.

What is the difference between voltage drop and wire ampacity?

Ampacity is the maximum current a wire can carry before it overheats and becomes a fire hazard. Voltage drop is the loss of voltage caused by wire resistance. A wire can be within its ampacity rating and still have unacceptable voltage drop. In low-voltage DC systems like 12V actuators, voltage drop is almost always the limiting factor — you will need to upsize the wire for voltage drop long before ampacity becomes a concern.

How do I reduce voltage drop in my wiring?

There are four ways to reduce voltage drop: (1) Use thicker wire — going from 18 AWG to 14 AWG cuts resistance by 60%. (2) Shorten the wire run — mount the power supply closer to the actuator. (3) Increase the supply voltage — 24V actuators have half the current of 12V for the same power, which cuts voltage drop by 75%. (4) Use a dedicated wire pair for each actuator instead of daisy-chaining multiple devices on one cable.