Electrical Cable Sizing
Selecting the correct electrical cable size ensures safe operation, minimizes voltage drop, prevents overheating, and provides adequate short-circuit protection for the entire installation.
Where:
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P = Power (Watts)
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V = Voltage (Volts)
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I = Current (Amps)
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PF = Power Factor
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η = Efficiency
Step 1: Calculate Load Current
For a 3-phase circuit:
For a single-phase circuit:
Step 2: Select the Cable Size
Choose a cable with an ampacity greater than the calculated load current after applying all installation correction factors.
Consider:
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Ambient temperature
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Installation method (tray, conduit, buried, etc.)
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Number of grouped cables
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Cable insulation type
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Voltage drop
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Short-circuit withstand capacity
Step 3: Perform a Voltage Drop Check
For a 3-phase circuit:
Where:
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L = Cable length
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R = Resistance
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X = Reactance
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ϕ\phiϕ = Power factor angle
The final cable selection must satisfy both the required ampacity and the permissible voltage drop under the actual installation conditions.