Voltage Drop Calculator

How to Use — Voltage Drop Calculator Pro

Step 1: Open the Calculator

Go to numovix.com and open the Voltage Drop Calculator Pro tool. No sign-up needed, no data saved — calculations happen instantly in your browser.

Step 2: Enter Your Circuit Parameters

Fill in these 6 fields in the Circuit Details section:

| Field | What to Enter | Example |

| System Voltage | Select from dropdown: 120V, 208V, 240V, 277V, 480V, or enter a custom voltage. | 240V (for residential dryer circuit) |

| Load Current | Enter the amperage your device draws (from nameplate or clamp meter). | 30 A |

| One-Way Length | Distance from panel to load in feet (one-way, not round trip). | 150 ft |

| Conductor Material | Choose Copper or Aluminum. | Copper |

| Wire Size (AWG/kcmil) | Select your conductor size from NEC standard sizes. | 10 AWG |

| Phase | Pick Single-Phase (2-wire) or Three-Phase (3-wire). | Single-Phase |

Tip: If your voltage isn't listed, select "Custom Voltage" and type your value manually.

Step 3: Click "Calculate Voltage Drop"

Hit the orange Calculate Voltage Drop button. The tool instantly shows:

Voltage Drop (V) — How much voltage is lost in the wires
Voltage Drop (%) — Percentage of source voltage lost
End Voltage — Actual voltage reaching your load
NEC Compliance — Whether your design passes the 3% branch circuit and 5% total drop limits

Step 4: Read the Results Dashboard

After calculation, you'll see:

1. Hero Result — Big, bold voltage drop number with color coding (green = good, red = too high).

2. Summary Cards — Source voltage, drop, end voltage, drop %, load current, and max allowable length for 3% drop.

3. Circuit Breakdown — Side-by-side comparison cards for quick reference.

4. NEC Compliance Check — Green PASS, yellow WARNING, or red FAIL based on NEC recommendations.

5. Charts — Bar chart showing voltage drop % across all wire sizes, and line chart comparing end voltage vs. nominal.

6. Full AWG Table — Scrollable table with drop calculations for every wire size from 14 AWG to 1000 kcmil. Your selected size is highlighted.

7. Advanced Analytics — Power loss in watts, annual energy waste, estimated cost at $0.12/kWh, and the formula used.

8. NEC & Safety Tips — Context-aware advice based on your results (e.g., aluminum termination warnings, motor starting voltage, temperature derating).

Step 5: Optimize Your Design (If Needed)

If your voltage drop exceeds 3%:

Try a larger wire size (e.g., 10 AWG → 8 AWG) and recalculate.
Reduce the circuit length if possible.
Consider copper instead of aluminum for lower resistance.
For three-phase loads, verify you're using the correct phase setting.

If drop exceeds 5%:

This is a NEC concern. Resize the conductor immediately or consult a licensed electrician.

### Step 6: Reset & Recalculate

Click Reset to clear all fields and start a new calculation.

Quick Reference — NEC Voltage Drop Limits

| Limit | Allowed Drop | Typical Use |

| 3% | Branch circuits (feeders + branch) | Best practice for motors, HVAC, appliances |

| 5% | Total drop (service to load) | Maximum acceptable for general loads |

> Important: Voltage drop is an NEC Fine Print Note (FPN), not a hard enforceable rule — but inspectors often check it. Always verify against the latest NEC edition and local amendments.

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Who Should Use This Tool?

Electricians — Quick field calculations for wire sizing
HVAC Contractors — Verify voltage for compressor and motor circuits
Solar Installers — DC and AC voltage drop for long PV runs
DIY Homeowners — Plan circuits for EV chargers, workshops, outbuildings
Engineers — Preliminary design checks before detailed analysis

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Privacy Note

Numovix does not store, track, or transmit any data you enter. All calculations run locally in your browser. No account, no permissions, no cookies tracking your inputs.

Disclaimer: This calculator is for informational and educational purposes only. Always consult a licensed electrician and verify results against the latest National Electrical Code (NEC) before finalizing any electrical installation.