Cable Length Calculator
Calculate cable length requirements, voltage drop, and wire gauge for electrical installations. Determine proper cable sizing for optimal performance and safety.
Step 1: Electrical Parameters
Voltage Drop Formula
VD = (2 × L × R × I) / 1000
Where L = Length, R = Resistance, I = Current
Step 2: Cable Specifications
Common Cable Applications
14 AWG: Lighting circuits (15A max)
12 AWG: General outlets (20A max)
10 AWG: Kitchen appliances (30A max)
8 AWG: HVAC systems (40A max)
Cable Calculation Results
Recommended Wire Gauge
Wire Gauge Comparison
| Wire Gauge (AWG) | Max Current (A) | Resistance (Ω/1000ft) | Max Length (ft) at 120V/15A |
|---|
Voltage Drop Formula & Standards
Voltage Drop = (2 × Length × Resistance × Current) / 1000
Where:
• Length = One-way length of cable (feet)
• Resistance = Resistance per 1000ft for the wire gauge (Ω)
• Current = Load current in amps (A)
• 2 = Factor for single-phase (round trip)
For three-phase systems:
• Voltage Drop = (√3 × Length × Resistance × Current) / 1000
Standards:
• NEC recommends max 3% voltage drop for branch circuits
• Max 5% voltage drop for feeder and branch circuits combined
Example Calculation
Example: 120V, 15A, 100ft with 12 AWG Copper
Resistance of 12 AWG copper: 1.588 Ω/1000ft
Voltage Drop Calculation:
VD = (2 × 100 × 1.588 × 15) / 1000 =
(2 × 100 × 23.82) / 1000 =
4764 / 1000 = 4.764V
Percentage Voltage Drop:
(4.764V / 120V) × 100 = 3.97%
Power Loss:
Power Loss = Voltage Drop × Current = 4.764V × 15A = 71.46W
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