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Electrical Power Worked Examples

Worked examples for cable sizing, breaker rating, transformer, generator, kVA, ampacity, and power factor checks.

Cable Sizing & Voltage Drop Planner

Sample inputs: load: 75; voltage: 400; phase: three; pf: 0.85; length: 95; material: copper

  • Code / standard profile: GCC project planning
  • Calculated load current: 127.36 A
  • Selected cable ampacity estimate: 210.00 A
  • Ampacity margin: 64.9 %

Use at least 50 mm² as a preliminary cable size under these simplified assumptions.

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Electrical Load Schedule Builder

Sample inputs: lighting: 22; sockets: 35; hvac: 120; motors: 45; other: 18; demand: 75

  • Connected load: 240.00 kW
  • Demand load: 180.00 kW
  • Demand kVA: 204.55 kVA
  • kVA with spare capacity: 245.45 kVA

Use 245.45 kVA as the planning load after demand and spare capacity.

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Transformer Sizing & Spare Capacity Calculator

Sample inputs: load: 620; demand: 80; pf: 0.9; future: 20; maxLoading: 80

  • Demand load: 496.00 kW
  • Base transformer load: 551.11 kVA
  • Required kVA at loading target: 826.67 kVA
  • Recommended standard transformer: 1,000 kVA

Select approximately 1,000 kVA transformer capacity for the entered load and spare strategy.

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Generator Sizing & Starting Load Planner

Sample inputs: running: 180; pf: 0.8; motor: 45; startFactor: 2.5; diversity: 90; spare: 15

  • Running diversified load: 202.50 kVA
  • Starting allowance: 84.38 kVA
  • Peak kVA with spare: 329.91 kVA
  • Recommended generator size: 400 kVA

Plan around a 400 kVA generator before manufacturer step-load and voltage-dip verification.

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Power Factor Correction & Payback Calculator

Sample inputs: kw: 350; currentPf: 0.72; targetPf: 0.95; voltage: 400; monthlySaving: 2600; costPerKvar: 180

  • Required capacitor size: 222.31 kVAR
  • kVA before correction: 486.11 kVA
  • kVA after correction: 368.42 kVA
  • Transformer relief: 117.69 kVA

Install approximately 222.31 kVAR capacitor capacity to move from 0.72 PF to 0.95 PF.

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Conduit Fill Calculator

Sample inputs: conduitArea: 860; cableArea: 95; quantity: 3; fillLimit: 40; codeProfile: gcc

  • Code / standard profile: GCC project planning
  • Total conductor area: 285 mm²
  • Conduit fill: 33.1 %
  • Entered fill limit: 40 %

Fill is within the entered 40 % limit.

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Short Circuit Current Calculator

Sample inputs: kva: 1000; voltage: 400; impedance: 6; motorContribution: 10

  • Transformer full-load current: 1,443 A
  • Transformer fault current: 24.06 kA
  • With motor contribution: 26.46 kA
  • Impedance used: 6.00 %

Preliminary available fault current is about 26.46 kA at the transformer secondary.

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Lighting Lux Calculator

Sample inputs: area: 120; lux: 500; lumens: 4000; uf: 60; mf: 80

  • Target luminous flux at workplane: 60,000 lm
  • Adjusted required lumens: 125,000 lm
  • Recommended luminaire count: 32 fixtures
  • Installed lumen density: 1,042 lm/m²

Plan approximately 32 fixtures fixtures at 4,000 lm each before photometric verification.

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Breaker Size Calculator

Sample inputs: kw: 45; voltage: 400; phase: 3; pf: 0.9; margin: 25; codeProfile: gcc

  • Code / standard profile: GCC project planning
  • Load current: 72.2 A
  • Design current with margin: 90.2 A
  • Recommended breaker rating: 100 A

Use approximately a 100 A breaker before checking cable ampacity, trip curve, and fault rating.

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kVA to Amps Calculator

Sample inputs: kva: 100; voltage: 400; phase: 3

  • Apparent power: 100.00 kVA
  • Calculated current: 144.3 A
  • Phase: Three phase
  • Voltage used: 400 V

100.00 kVA equals about 144.3 A at 400 V three phase.

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Ampacity Derating Calculator

Sample inputs: baseAmpacity: 150; temperatureFactor: 91; groupingFactor: 80; installationFactor: 95; loadCurrent: 95; codeProfile: gcc

  • Code / standard profile: GCC project planning
  • Base ampacity: 150.0 A
  • Combined derating factor: 69.2 %
  • Derated ampacity: 103.7 A

Derated ampacity is above the entered load current.

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MEP Unit Converter

Sample inputs: value: 1200; conversion: cfm-lps

  • Input value: 1,200.00
  • Converted value: 566.336 L/s
  • Conversion factor: 1 CFM = 0.471947 L/s

1,200.00 converts to 566.336 L/s.

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