Definition of Voltage Drop
Voltage drop is the decrease in voltage that occurs as current flows through a wire or circuit. Wire has resistance, which converts some of your electrical energy into heat. The longer and thinner the wire, the higher the resistance, and the more voltage you lose before power reaches the device.
In a home 240-volt circuit, a 12-volt drop may go unnoticed. In a 12 or 24 volt boat system, a 1 volt drop can make lights look dull and electronics act up.
Key idea
More length means more loss. More cross-sectional area means less loss.
Synonyms
Volt drop
Why Voltage Drop Matters On Boats
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Most marine lighting uses 12 or 24 volts. Small drops hurt brightness fast.
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LEDs can dim or shift color when voltage sags.
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Pumps and electronics can run hot or unstable when supply voltage is low.
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ABYC best practice is to keep lighting circuits under about 3 percent drop for consistent performance.
How To Minimize Voltage Drop
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Use a thicker cable gauge for lower resistance.
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Shorten wire runs when you can.
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Use quality power supplies and LED drivers to stabilize output.
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Keep connections tight and corrosion-free with marine-grade terminals and heat-shrink.
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Home-run critical lighting zones instead of daisy chaining long strings.
Recommended DRSA Products That Help Beat Voltage Drop
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Marine-grade wire and cable, tinned copper for low resistance and corrosion protection
→ drsa.com: Wire & Cable -
Heat-shrink terminals and connectors for tight, sealed joints
→ drsa.com: Connectors & Heat-Shrink -
LED drivers and power supplies to stabilize voltage to fixtures
→ drsa.com: LED Drivers & Power Supplies -
PWM dimmers designed for low-voltage LED modules without flicker
→ drsa.com: LED Dimmers -
Engine room and utility lights with efficient electronics that tolerate long runs better
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Navigation and deck lights that are optimized for 12 or 24 volt service
→ drsa.com: Navigation Lights -
Deck & Courtesy Lights
The Simple Math You Can Use Today
The basic relationship is:
Vdrop = I × R
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I is current in amps
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R is the total circuit resistance in ohms, out and back
For marine wire, resistance depends on gauge and length. Use the total round-trip length in feet or meters when you check a table.
Target
Keep lighting circuits under about 3 percent drop.
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12 V system, 3 percent is 0.36 V
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24 V system, 3 percent is 0.72 V
Quick Wire Gauge Tips
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Long run with modest current, step up the gauge even if it feels oversized.
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Parallel home runs to clusters of lights to keep each branch short.
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Use tinned, marine-grade copper only.
Rule of thumb
If your lights dim when everything else kicks on, or they brighten when the engine alternator comes online, voltage drop is likely.
Worked Example
Goal
A 12 V courtesy light circuit draws 3 A total across several fixtures. The panel is 25 feet from the lights. Round-trip length is 50 feet. You want under 3 percent drop, which is 0.36 V.
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Look up wire resistance per foot for your candidate gauge.
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Calculate Vdrop at 50 feet round trip.
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Choose the gauge that keeps Vdrop below 0.36 V.
If 16 AWG gives you about 0.5 V drop in that scenario, move to 14 AWG or 12 AWG until the math lands below 0.36 V. When in doubt, upsize. Copper is cheaper than troubleshooting.
Frequently Asked Questions
What causes voltage drop on boats?
Resistance in long or thin wires. Every foot adds a little loss. Thin gauges add more. Corroded or loose connections make it worse.
How much drop is too much?
Keep lighting circuits under about 3 percent. More than that risks dim output and unstable electronics.
Does voltage drop affect LEDs?
Yes. LEDs dim and can shift color when voltage sags. Use proper gauge wire and regulated LED drivers to hold output steady: https://www.drsa.com/collections/led-drivers
Can I calculate voltage drop myself?
Yes. Use V = I × R and round-trip length with the resistance value for your wire gauge. If you are not sure, choose a thicker cable.
Is voltage drop worse in DC or AC?
It shows up more on DC boat systems since the supply is low voltage and the wire runs can be long for the size of the circuit.
What should I buy first to fix it?
Start with tinned marine wire in the right gauge and proper heat-shrink connectors, then stabilize your fixtures with drivers where needed
Why Choose DRSA To Combat Voltage Drop
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Marine-grade materials that resist corrosion and maintain low resistance.
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Efficient drivers and fixtures that deliver steady brightness.
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Parts that install cleanly, with clear specs and real support.
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Trusted by yards and owners since 1988.
Popular starting points
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Pacific G4 Engine Room Light for bright, efficient utility lighting:
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LED Drivers & Power Supplies to keep voltage stable:
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Wire & Cable for proper gauge upgrades:
Need Help Choosing Wire Gauge or Drivers?
Tell us your system voltage, total load in amps, and round-trip length. We will recommend the right wire gauge, driver, and connection kit from DRSA to keep your lights bright and reliable.