Introduction #

Accurate factory load calculation is the foundation of safe, efficient, and cost-effective electrical system design for industrial facilities. Whether you're designing a new manufacturing plant, expanding an existing facility, or optimizing electrical infrastructure, understanding how to properly calculate and manage factory loads is essential. This guide provides practical implementation strategies specifically tailored for industrial facilities, covering manufacturing plants, warehouses, processing facilities, and mixed-use industrial buildings.

Understanding Factory Load in Industrial Context #

What Constitutes Factory Load #

Factory load encompasses all electrical power requirements in an industrial facility:

Production Equipment:

  • Manufacturing machinery
  • Assembly lines
  • Process equipment
  • Material handling systems

Support Systems:

  • Lighting (production, warehouse, office)
  • HVAC (heating, cooling, ventilation)
  • Compressed air systems
  • Water and wastewater treatment

Auxiliary Systems:

  • Office equipment
  • Security systems
  • Fire protection
  • Communication systems

Why Factory Load Calculation Matters #

Safety:

  • Prevents overloads and fires
  • Ensures proper protection
  • Meets code requirements

Cost Optimization:

  • Right-size equipment
  • Avoid oversizing
  • Optimize utility costs

Reliability:

  • Prevents downtime
  • Ensures adequate capacity
  • Supports future growth

Step 1: Facility Assessment and Load Inventory #

Manufacturing Plant Load Inventory #

Production Equipment:

CNC machines: 8 × 15 kW = 120 kW
Welding equipment: 6 × 12 kW = 72 kW
Assembly machines: 12 × 5 kW = 60 kW
Conveyor systems: 4 × 8 kW = 32 kW
Packaging equipment: 6 × 4 kW = 24 kW
Total production: 308 kW

Support Systems:

Compressed air: 2 × 30 kW = 60 kW
Lighting (production): 25 kW
Lighting (warehouse): 15 kW
Lighting (office): 5 kW
HVAC (production): 80 kW
HVAC (warehouse): 40 kW
HVAC (office): 12 kW
Total support: 237 kW

Total Connected Load:

308 + 237 = 545 kW

Warehouse Load Inventory #

Material Handling:

Forklifts (electric): 15 × 8 kW = 120 kW
Conveyor systems: 8 × 6 kW = 48 kW
Sorting equipment: 4 × 10 kW = 40 kW
Dock equipment: 10 × 2 kW = 20 kW
Total material handling: 228 kW

Building Services:

Lighting: 50 kW
HVAC: 60 kW
Battery chargers: 8 × 5 kW = 40 kW
Security: 5 kW
Total services: 155 kW

Total Connected Load:

228 + 155 = 383 kW

Step 2: Apply Industry-Specific Diversity Factors #

Manufacturing Plant Diversity #

Production Equipment:

  • CNC machines: 0.75-0.85 (not all run simultaneously)
  • Welding: 0.30-0.50 (intermittent operation)
  • Assembly: 0.70-0.80 (production cycles)
  • Conveyors: 0.80-0.90 (continuous but variable speed)

Support Systems:

  • Compressed air: 0.80-0.90 (demand-based)
  • Lighting: 0.90-1.0 (most on during operation)
  • HVAC: 0.60-0.80 (seasonal and occupancy-based)

Example Calculation:

Production: 308 kW × 0.75 = 231 kW
Support: 237 kW × 0.75 = 177.75 kW
Diversified load: 231 + 177.75 = 408.75 kW

Warehouse Diversity #

Material Handling:

  • Forklifts: 0.60-0.70 (not all operating simultaneously)
  • Conveyors: 0.70-0.85 (variable operation)
  • Sorting: 0.75-0.85 (peak vs average)

Building Services:

  • Lighting: 0.85-0.95 (zoning and controls)
  • HVAC: 0.60-0.75 (minimal conditioning)
  • Battery chargers: 0.40-0.60 (staggered charging)

Example Calculation:

Material handling: 228 kW × 0.65 = 148.2 kW
Services: 155 kW × 0.70 = 108.5 kW
Diversified load: 148.2 + 108.5 = 256.7 kW

Step 3: Calculate Power Factor and kVA #

Manufacturing Plant Power Factor #

Load Breakdown:

Motors (production): 200 kW at 0.85 PF = 235.3 kVA
Welding: 50 kW at 0.70 PF = 71.4 kVA
Lighting: 45 kW at 1.0 PF = 45.0 kVA
HVAC: 132 kW at 0.85 PF = 155.3 kVA
Office: 20 kW at 0.90 PF = 22.2 kVA

Total kW: 447 kW
Total kVA: 529.2 kVA
Weighted PF: 447 ÷ 529.2 = 0.845

Warehouse Power Factor #

Load Breakdown:

Material handling: 148.2 kW at 0.85 PF = 174.4 kVA
Lighting: 42.5 kW at 1.0 PF = 42.5 kVA
HVAC: 42 kW at 0.85 PF = 49.4 kVA
Chargers: 24 kW at 0.95 PF = 25.3 kVA

Total kW: 256.7 kW
Total kVA: 291.6 kVA
Weighted PF: 256.7 ÷ 291.6 = 0.880

Step 4: Account for Future Growth #

Growth Planning #

Manufacturing Plant:

Current diversified: 408.75 kW
Planned expansion: +100 kW (new production line)
Future diversified: (408.75 + 100) × 0.75 = 381.6 kW
Total with growth: 408.75 + 75 = 483.75 kW

Warehouse:

Current diversified: 256.7 kW
Planned expansion: +50 kW (additional material handling)
Future diversified: (256.7 + 50) × 0.65 = 199.5 kW
Total with growth: 256.7 + 32.5 = 289.2 kW

Step 5: Add Safety Margins #

Standard Safety Margins #

Manufacturing Plant:

Design load: 483.75 kW × 1.20 = 580.5 kW
Design kVA: 580.5 ÷ 0.845 = 687.0 kVA

Warehouse:

Design load: 289.2 kW × 1.15 = 332.6 kW
Design kVA: 332.6 ÷ 0.880 = 378.0 kVA

Step 6: Equipment Sizing #

Manufacturing Plant Equipment #

Transformer Selection:

Required: 687.0 kVA
Standard sizes: 500, 750, 1000 kVA
Selected: 750 kVA transformer

Main Breaker:

Current: 687,000 ÷ (√3 × 480) = 826.5 A
Selected: 1000 A breaker (with 20% margin)

Generator (if required):

Selected: 750 kVA generator

Warehouse Equipment #

Transformer Selection:

Required: 378.0 kVA
Standard sizes: 300, 400, 500 kVA
Selected: 400 kVA transformer

Main Breaker:

Current: 378,000 ÷ (√3 × 480) = 454.7 A
Selected: 600 A breaker (with margin)

Special Considerations for Industrial Facilities #

Motor Starting Currents #

Large Motor Impact:

Largest motor: 50 HP = 37.3 kW
Starting current: 6× rated = 223.8 kW
During start: 580.5 - 37.3 + 223.8 = 767.0 kW

Solutions:

  • Use reduced-voltage starters
  • Stagger motor starts
  • Size transformer for starting (if critical)

Process Load Variations #

Peak vs Average:

Average load: 580.5 kW
Peak load: 650 kW (during production surges)
Design for: 650 kW (peak conditions)

Harmonic Loads #

Non-Linear Equipment:

VFDs: 100 kW
Harmonic content: 25% THD
Derating factor: 0.80
Effective capacity: 580.5 ÷ 0.80 = 725.6 kVA

Load Management Strategies #

Peak Shaving #

Strategy: Reduce peak demand to lower utility charges

Methods:

  • Shift non-critical loads
  • Use energy storage
  • Implement load scheduling
  • Optimize production timing

Load Balancing #

Strategy: Balance loads across phases

Benefits:

  • Reduced neutral current
  • Better voltage regulation
  • Improved efficiency
  • Lower losses

Demand Response #

Strategy: Reduce load during utility peak periods

Implementation:

  • Automated load shedding
  • Production scheduling
  • Energy storage systems
  • Generator backup

Frequently Asked Questions #

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

A:

  • Monitor actual usage patterns
  • Review production schedules
  • Measure peak vs average loads
  • Use industry standards as starting point
  • Adjust based on observations

Q2: What's the typical power factor for manufacturing facilities? #

A:

  • Good: 0.90-0.95 (with correction)
  • Typical: 0.85-0.90 (mixed loads)
  • Poor: 0.75-0.85 (many motors, no correction)

Q3: How much safety margin should I add? #

A:

  • 15-20%: Standard applications
  • 20-25%: Facilities with growth plans
  • 25-30%: Critical applications or variable loads

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

A: Size for design peak load (diversified load with safety margin). This ensures equipment can handle worst-case scenarios.

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

A:

  • Use reduced-voltage starters for large motors
  • Stagger motor starts
  • Size transformer for starting (if critical)
  • Consider soft starters or VFDs

Q6: What's the impact of harmonics on factory loads? #

A: Harmonics increase losses and reduce effective capacity. Apply derating factors:

  • Low harmonics: 0.95-1.0
  • Moderate: 0.85-0.95
  • High: 0.70-0.85

Conclusion #

Factory load calculation for industrial facilities requires careful consideration of:

  • Complete load inventory (all equipment and systems)
  • Industry-specific diversity factors (based on operating patterns)
  • Power factor (weighted average across all loads)
  • Future growth (planned expansion)
  • Safety margins (appropriate headroom)
  • Special considerations (motor starting, harmonics, 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 factors based on your specific operations and requirements.