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What’s Voltage Drop and Why Does It Matter?

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HOW TO PREVENT VOLTAGE DROP

The most effective solution to prevent voltage drop is upsizing to the next conductor. Alternatively, you can run parallel conductors or install a second circuit—sometimes running an additional 500/3 cable is more cost-effective than upsizing
 

Another effective strategy is to keep circuit runs as short as practical. For long runs, consider relocating equipment closer to the power source.
 

VOLTAGE DROP FACTORS

  • Wire Size/Gauge: Smaller wire = higher resistance = more voltage drop. Larger conductors allow electricity to flow more easily.
     
  • Length of Conductor: Distance is often the biggest factor. A circuit that works at 50 feet may have serious problems at 200 feet.
     
  • Load Current: Higher current means more voltage drop. A 20-amp circuit experiences twice the voltage drop of a 10-amp circuit.
     
  • Temperature: Higher temperatures increase resistance. Bundled cables or hot environments increase voltage drop.
     
  • Installation Conditions: Heat dissipation varies by installation type. Free air provides the best performance, while PVC conduit and underground installations retain more heat and increase resistance.
     

Voltage drop is the loss of voltage as electricity travels through wire or cable. Like water pressure decreasing as it flows through a long hose, when current moves through a conductor, resistance causes some voltage to be lost along the way.

Understanding voltage drop and how to minimize it is essential for any wire & cable installation. While some voltage drop is inevitable, excessive amounts cause serious problems: motors overheat and fail to start, lights dim, and sensitive electronics malfunction.
 

WHAT CAUSES VOLTAGE DROP

All conductors, regardless of material, have some electrical resistance. When current flows through the conductor, the electrical energy gets converted to heat, resulting in less voltage at the end of the circuit.

This is described by Ohm's Law: 

For acceptable voltage drop levels, the NEC recommends:

  • 3% maximum for branch circuits
  • 5% maximum combined for feeders and branch circuits

These are recommendations, not strict requirements, but following them ensures efficient operation and prevents equipment problems.
 

KEY FACTORS THAT AFFECT VOLTAGE DROP

Several factors influence how much voltage drop occurs in a wire & cable installation.

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DISTANCE is the biggest factor that causes voltage drop. Due to compounding resistance, a circuit that works perfectly at 50 feet may have serious problems at 200 feet.
 

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The amount of CURRENT flowing through the wire matters. For example, a 20-amp circuit experiences twice the voltage drop of a 10-amp circuit with the same wire size over the same distance.
 

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WIRE SIZE plays a major role. Smaller wires have higher resistance and cause more voltage drop, while larger conductors allow electricity to flow more easily.
 

Distance Icon

HIGHER TEMPERATURES increase resistance, and bundled cables or hot environments increase voltage drop. PVC conduit and underground installations retain more heat and increase resistance, especially in hot climates where soil temperatures are high.

 

UNDERSIZED VS PROPER SIZED WIRE

The most effective solutoin for preventing voltage drop is upsizing to the next conductor. However, there are several methods to consider.

  • One option is to run parallel conductors or install an additional circuit—sometimes running an additional 500/3 cable is more cost-effective than upsizing to 600/3 or 750/3, for example.
     
  • Keeping circuit runs as short as possible can minimize voltage drop. It is ideal to relocate equipment closer to the power source for long runs.
     
  • Maintaining a cooler environment with proper airflow will provide the best performance because heat can escape easily.
     

 

 

FACTOR UNDERSIZED WIRE PROPERLY SIZED WIRE
Voltage Drop Excessive (>5%) Within Limits (≤3%)
Equipment Performance Motors overhead; lights dim Operates at rated capacity
Long-Term Costs Higher energy costs; premature failure Lower costs; full lifespan
Safety Overheating risk Safe, reliable operation

 

 

White QuotationsService Wire is always responsive to RFQs and knowledgable about wire and cable products.

 

White QuotationsService Wire goes above and beyond to help us meet our customer's needs.

SPECIFICATION REVIEW

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Service Wire manufactures wire and cable specifically engineered for optimal conductivity and minimal voltage drop. Our technical team can help you select the right conductor size, material, and configuration for your specific application—whether it's a long run to an outbuilding, a high-current motor circuit, or a sensitive electronics installation.

Don't let voltage drop compromise your installation. Contact your Service Wire representative today to request a free specification audit to ensure you're specifying the right wire for the job.

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