Introduction #

While understanding the theory of factory load calculation is important, seeing real-world examples helps bridge the gap between theory and practice. This guide provides detailed, step-by-step calculations for various industrial facility types, from small manufacturing plants to large warehouses. Each example includes actual equipment lists, diversity factors, power factor considerations, and final equipment sizing decisions.

Example 1: Small Manufacturing Plant #

Facility Overview #

  • Type: Light manufacturing facility
  • Size: 1,500 m² production area + 300 m² office
  • Operations: Assembly, packaging, quality control
  • Operating Hours: 8 hours/day, 5 days/week

Equipment Inventory #

Equipment Quantity Power per Unit (kW) Total (kW) Power Factor
Assembly machines 8 5.0 40.0 0.85
Conveyor belts 3 3.0 9.0 0.80
Packaging machines 4 2.5 10.0 0.85
Quality control equipment 2 1.5 3.0 0.90
Compressed air system 1 15.0 15.0 0.85
Lighting (production) - - 12.0 1.0
Lighting (office) - - 3.0 1.0
HVAC (production) 1 25.0 25.0 0.85
HVAC (office) 1 8.0 8.0 0.85
Office equipment - - 5.0 0.90
Total Connected 130.0 kW

Step 1: Apply Diversity Factors #

Load Category Connected (kW) Diversity Factor Diversified (kW)
Production equipment 62.0 0.75 46.5
Lighting (production) 12.0 0.95 11.4
Lighting (office) 3.0 0.90 2.7
HVAC (production) 25.0 0.70 17.5
HVAC (office) 8.0 0.80 6.4
Office equipment 5.0 0.60 3.0
Compressed air 15.0 0.85 12.8
Total Diversified 100.3 kW

Step 2: Calculate Weighted Power Factor #

Production equipment: 46.5 kW at 0.85 PF
Lighting: 14.1 kW at 1.0 PF
HVAC: 23.9 kW at 0.85 PF
Office: 3.0 kW at 0.90 PF
Compressed air: 12.8 kW at 0.85 PF

Weighted PF = Total kW ÷ Total kVA

kVA_production = 46.5 ÷ 0.85 = 54.7 kVA
kVA_lighting = 14.1 ÷ 1.0 = 14.1 kVA
kVA_HVAC = 23.9 ÷ 0.85 = 28.1 kVA
kVA_office = 3.0 ÷ 0.90 = 3.3 kVA
kVA_air = 12.8 ÷ 0.85 = 15.1 kVA

Total kVA = 54.7 + 14.1 + 28.1 + 3.3 + 15.1 = 115.3 kVA
Weighted PF = 100.3 ÷ 115.3 = 0.87

Step 3: Add Safety Margin #

Design Load = 100.3 kW × 1.20 (20% margin) = 120.4 kW
Design kVA = 115.3 × 1.20 = 138.4 kVA

Step 4: Equipment Selection #

  • Transformer: 150 kVA (next standard size)
  • Main Breaker: 200 A (138.4 kVA ÷ (√3 × 400V) = 200 A, with 25% margin)
  • Generator (if required): 150 kVA

Key Takeaways #

  • Diversity factors significantly reduce calculated load (130 kW → 100.3 kW)
  • Weighted power factor (0.87) is better than individual equipment PFs
  • 20% safety margin provides headroom for future expansion

Example 2: Large Warehouse with Distribution Center #

Facility Overview #

  • Type: Distribution warehouse
  • Size: 5,000 m² storage + 500 m² office
  • Operations: Material handling, sorting, shipping
  • Operating Hours: 16 hours/day, 6 days/week

Equipment Inventory #

Equipment Quantity Power per Unit (kW) Total (kW) Power Factor
Forklifts (electric) 12 8.0 96.0 0.85
Conveyor systems 6 7.5 45.0 0.80
Sorting machines 4 10.0 40.0 0.85
Dock levelers 8 2.0 16.0 0.90
Battery chargers 6 5.0 30.0 0.95
Lighting (warehouse) - - 40.0 1.0
Lighting (office) - - 5.0 1.0
HVAC (warehouse) 2 30.0 60.0 0.85
HVAC (office) 1 12.0 12.0 0.85
Office equipment - - 8.0 0.90
Security systems - - 3.0 0.95
Total Connected 355.0 kW

Step 1: Apply Diversity Factors #

Load Category Connected (kW) Diversity Factor Diversified (kW)
Material handling 181.0 0.65 117.7
Lighting (warehouse) 40.0 0.90 36.0
Lighting (office) 5.0 0.90 4.5
HVAC (warehouse) 60.0 0.60 36.0
HVAC (office) 12.0 0.80 9.6
Office equipment 8.0 0.60 4.8
Security 3.0 1.0 3.0
Battery chargers 30.0 0.50 15.0
Total Diversified 226.6 kW

Note: Forklifts have low diversity (0.65) because not all operate simultaneously. Battery chargers have very low diversity (0.50) as charging is staggered.

Step 2: Calculate Weighted Power Factor #

Material handling: 117.7 kW at 0.85 PF = 138.5 kVA
Lighting: 40.5 kW at 1.0 PF = 40.5 kVA
HVAC: 45.6 kW at 0.85 PF = 53.6 kVA
Office: 4.8 kW at 0.90 PF = 5.3 kVA
Security: 3.0 kW at 0.95 PF = 3.2 kVA
Chargers: 15.0 kW at 0.95 PF = 15.8 kVA

Total kVA = 138.5 + 40.5 + 53.6 + 5.3 + 3.2 + 15.8 = 256.9 kVA
Weighted PF = 226.6 ÷ 256.9 = 0.88

Step 3: Add Safety Margin and Future Expansion #

Design Load = 226.6 kW × 1.25 (25% margin for expansion) = 283.3 kW
Design kVA = 256.9 × 1.25 = 321.1 kVA

Step 4: Equipment Selection #

  • Transformer: 400 kVA (next standard size above 321.1 kVA)
  • Main Breaker: 500 A (321.1 kVA ÷ (√3 × 400V) = 463 A, rounded up)
  • Generator (if required): 400 kVA

Key Takeaways #

  • Material handling equipment dominates the load
  • Battery charger diversity is critical (staggered charging reduces peak demand)
  • 25% margin accommodates future expansion and peak operations

Example 3: Mixed-Use Industrial Facility #

Facility Overview #

  • Type: Manufacturing + Warehouse + Office
  • Size: 2,000 m² manufacturing + 1,500 m² warehouse + 400 m² office
  • Operations: Production, storage, administration
  • Operating Hours: 10 hours/day, 5 days/week

Equipment Inventory #

Equipment Quantity Power per Unit (kW) Total (kW) Power Factor
CNC machines 6 12.0 72.0 0.85
Welding equipment 4 15.0 60.0 0.70
Material handling 3 5.0 15.0 0.85
Compressed air 1 22.0 22.0 0.85
Lighting (production) - - 18.0 1.0
Lighting (warehouse) - - 12.0 1.0
Lighting (office) - - 4.0 1.0
HVAC (production) 1 35.0 35.0 0.85
HVAC (warehouse) 1 20.0 20.0 0.85
HVAC (office) 1 10.0 10.0 0.85
Office equipment - - 6.0 0.90
Total Connected 274.0 kW

Step 1: Apply Diversity Factors #

Load Category Connected (kW) Diversity Factor Diversified (kW)
CNC machines 72.0 0.80 57.6
Welding 60.0 0.40 24.0
Material handling 15.0 0.70 10.5
Compressed air 22.0 0.85 18.7
Lighting (all) 34.0 0.95 32.3
HVAC (all) 65.0 0.70 45.5
Office equipment 6.0 0.60 3.6
Total Diversified 192.2 kW

Note: Welding has very low diversity (0.40) because welders operate intermittently, not continuously.

Step 2: Calculate Weighted Power Factor #

CNC: 57.6 kW at 0.85 PF = 67.8 kVA
Welding: 24.0 kW at 0.70 PF = 34.3 kVA (low PF!)
Material handling: 10.5 kW at 0.85 PF = 12.4 kVA
Compressed air: 18.7 kW at 0.85 PF = 22.0 kVA
Lighting: 32.3 kW at 1.0 PF = 32.3 kVA
HVAC: 45.5 kW at 0.85 PF = 53.5 kVA
Office: 3.6 kW at 0.90 PF = 4.0 kVA

Total kVA = 67.8 + 34.3 + 12.4 + 22.0 + 32.3 + 53.5 + 4.0 = 226.3 kVA
Weighted PF = 192.2 ÷ 226.3 = 0.85

Step 3: Power Factor Correction Consideration #

Welding equipment creates low power factor (0.70). Consider power factor correction:

Before Correction:

  • Total kVA: 226.3 kVA
  • Utility penalty likely (PF < 0.90)

After Correction (target PF = 0.95):

Required kVA = 192.2 ÷ 0.95 = 202.3 kVA
kVAR reduction = 226.3 - 202.3 = 24.0 kVAR

Install 25 kVAR capacitor bank to improve power factor to 0.95.

Step 4: Add Safety Margin #

Design Load = 192.2 kW × 1.20 = 230.6 kW
Design kVA (corrected) = 202.3 × 1.20 = 242.8 kVA

Step 5: Equipment Selection #

  • Transformer: 250 kVA (with power factor correction)
  • Main Breaker: 400 A (242.8 kVA ÷ (√3 × 400V) = 350 A, with margin)
  • Power Factor Correction: 25 kVAR capacitor bank
  • Generator (if required): 250 kVA

Key Takeaways #

  • Welding equipment significantly impacts power factor
  • Power factor correction reduces kVA requirement by 10.6% (226.3 → 202.3 kVA)
  • Mixed-use facilities require careful diversity factor selection

Example 4: Food Processing Plant #

Facility Overview #

  • Type: Food processing and packaging
  • Size: 3,000 m² processing + 1,000 m² cold storage + 300 m² office
  • Operations: Processing, refrigeration, packaging
  • Operating Hours: 12 hours/day, 6 days/week

Equipment Inventory #

Equipment Quantity Power per Unit (kW) Total (kW) Power Factor
Processing equipment 10 8.0 80.0 0.85
Refrigeration compressors 4 25.0 100.0 0.85
Packaging machines 6 4.0 24.0 0.85
Conveyor systems 5 3.0 15.0 0.80
Lighting (processing) - - 20.0 1.0
Lighting (cold storage) - - 8.0 1.0
Lighting (office) - - 3.0 1.0
HVAC (office) 1 8.0 8.0 0.85
Office equipment - - 4.0 0.90
Total Connected 262.0 kW

Step 1: Apply Diversity Factors #

Load Category Connected (kW) Diversity Factor Diversified (kW)
Processing 80.0 0.75 60.0
Refrigeration 100.0 0.90 90.0
Packaging 24.0 0.80 19.2
Conveyors 15.0 0.70 10.5
Lighting 31.0 0.95 29.5
HVAC 8.0 0.80 6.4
Office 4.0 0.60 2.4
Total Diversified 218.0 kW

Note: Refrigeration has high diversity (0.90) because compressors run continuously to maintain temperature.

Step 2: Calculate Weighted Power Factor #

Processing: 60.0 kW at 0.85 PF = 70.6 kVA
Refrigeration: 90.0 kW at 0.85 PF = 105.9 kVA
Packaging: 19.2 kW at 0.85 PF = 22.6 kVA
Conveyors: 10.5 kW at 0.80 PF = 13.1 kVA
Lighting: 29.5 kW at 1.0 PF = 29.5 kVA
HVAC: 6.4 kW at 0.85 PF = 7.5 kVA
Office: 2.4 kW at 0.90 PF = 2.7 kVA

Total kVA = 70.6 + 105.9 + 22.6 + 13.1 + 29.5 + 7.5 + 2.7 = 251.9 kVA
Weighted PF = 218.0 ÷ 251.9 = 0.86

Step 3: Add Safety Margin #

Design Load = 218.0 kW × 1.20 = 261.6 kW
Design kVA = 251.9 × 1.20 = 302.3 kVA

Step 4: Equipment Selection #

  • Transformer: 315 kVA (next standard size)
  • Main Breaker: 500 A (302.3 kVA ÷ (√3 × 400V) = 436 A, with margin)
  • Generator (if required): 315 kVA

Key Takeaways #

  • Refrigeration dominates the load (90 kW, 41% of total)
  • High diversity for refrigeration (continuous operation)
  • Food processing requires reliable power (consider backup)

Common Calculation Mistakes to Avoid #

Mistake 1: Using Nameplate Ratings Without Diversity #

Error: Adding all nameplate ratings directly (355 kW in Example 2).

Correct: Apply appropriate diversity factors (226.6 kW after diversity).

Mistake 2: Ignoring Power Factor #

Error: Assuming kW = kVA for all loads.

Correct: Calculate weighted power factor and convert to kVA for equipment sizing.

Mistake 3: Overestimating Diversity Factors #

Error: Using 0.95 diversity for all equipment.

Correct: Use realistic diversity based on actual operating patterns (welding: 0.40, lighting: 0.95).

Mistake 4: Not Accounting for Future Expansion #

Error: Sizing exactly at calculated load.

Correct: Add 15-25% safety margin for future growth and peak conditions.

Frequently Asked Questions #

Q1: How do I determine diversity factors for my facility? #

A: Diversity factors depend on operating patterns:

  • Continuous operation: 0.90-1.0 (refrigeration, critical processes)
  • Intermittent operation: 0.60-0.80 (production equipment, material handling)
  • Rare operation: 0.30-0.50 (welding, backup equipment)

Monitor actual usage patterns and adjust factors accordingly.

Q2: What if I don't know the power factor of my equipment? #

A: Use typical values:

  • Motors: 0.80-0.90
  • Lighting (LED): 0.95-1.0
  • Lighting (fluorescent): 0.85-0.95
  • Welding: 0.60-0.75
  • Office equipment: 0.90-0.95

Measure with a power quality meter for accuracy.

Q3: How much safety margin should I add? #

A: Typical margins:

  • 15-20%: Standard facilities with predictable loads
  • 20-25%: Facilities with growth plans or variable loads
  • 25-30%: Critical facilities requiring high reliability

Q4: Should I size for peak load or average load? #

A: Size for design peak load (calculated diversified load with safety margin). This ensures equipment can handle worst-case scenarios while operating efficiently most of the time.

Q5: How do I account for motor starting currents? #

A: Motor starting currents (5-7× rated current) are typically handled by:

  • Circuit breakers: Sized for running current, with time-delay for starting
  • Transformers: Sized for running load (starting is brief)
  • Generators: May need 1.5-2× capacity for motor starting

Q6: What's the difference between connected load and demand load? #

A:

  • Connected load: Sum of all equipment nameplate ratings
  • Demand load: Connected load × diversity factor
  • Design load: Demand load × safety margin

Equipment is sized based on design load.

Conclusion #

These real-world examples demonstrate that factory load calculation requires careful consideration of:

  • Equipment inventory: Complete list of all electrical loads
  • Diversity factors: Realistic assessment of simultaneous operation
  • Power factor: Weighted average across all loads
  • Safety margins: Appropriate headroom for growth and peaks

Use the Factory Load Calculator to quickly estimate loads, but always verify with detailed calculations for final equipment selection. Each facility is unique, so adjust diversity factors and margins based on your specific operating patterns and requirements.