Introduction #

One of the most common mistakes in factory electrical design is confusing connected load with demand load. This misunderstanding leads to oversized equipment, wasted capital, and inefficient systems. Understanding the difference isn't just academic—it directly impacts your breaker sizing, transformer selection, and monthly energy costs. This guide explains both concepts with real engineering examples and shows you how to apply them correctly.

What is Connected Load? #

Connected load (also called "installed load" or "nameplate load") is the sum of all equipment nameplate ratings in your facility. It represents the theoretical maximum power if every device operated simultaneously at full capacity.

Characteristics of Connected Load #

  • Simple addition: Just add up all nameplate kW ratings
  • No time consideration: Assumes all equipment runs 24/7 at full load
  • No diversity: Assumes everything operates simultaneously
  • Upper bound: This is the absolute maximum possible load

Example: Calculating Connected Load #

Consider a small manufacturing facility:

Equipment Quantity Nameplate Rating (kW) Total Connected (kW)
CNC machines 5 15.0 75.0
Welding stations 3 25.0 75.0
Compressed air system 1 30.0 30.0
Lighting - - 20.0
HVAC 1 40.0 40.0
Office equipment - - 10.0
Total Connected Load 250.0 kW

This 250 kW is the connected load—the sum of all nameplate ratings.

What is Demand Load? #

Demand load (also called "diversified load" or "actual demand") is the realistic power requirement accounting for:

  • Equipment not operating simultaneously
  • Equipment not running at full capacity
  • Time-based usage patterns
  • Diversity factors

How Demand Load Differs #

Demand load = Connected Load × Diversity Factor × Demand Factor

Where:

  • Diversity Factor: Accounts for equipment not operating simultaneously
  • Demand Factor: Accounts for equipment not running at full capacity

Example: Calculating Demand Load #

Using the same facility, apply realistic diversity factors:

Load Category Connected (kW) Diversity Factor Demand Load (kW)
CNC machines 75.0 0.70 52.5
Welding stations 75.0 0.40 30.0
Compressed air 30.0 0.85 25.5
Lighting 20.0 0.95 19.0
HVAC 40.0 0.75 30.0
Office equipment 10.0 0.60 6.0
Total Demand Load 163.0 kW

Key Insight: The demand load (163 kW) is 35% lower than connected load (250 kW). This difference is critical for equipment sizing.

Why the Difference Matters #

Equipment Sizing Impact #

If you size for connected load (250 kW):

  • Transformer: 300 kVA (oversized)
  • Main breaker: 400 A (oversized)
  • Cost: $15,000+ in unnecessary equipment

If you size for demand load (163 kW):

  • Transformer: 200 kVA (appropriate)
  • Main breaker: 250 A (appropriate)
  • Cost: Correct sizing, optimal efficiency

Real-World Consequences #

Case Study: Oversized System

A facility designer sized a 500 kVA transformer based on connected load. The actual demand load was 280 kVA. Result:

  • Transformer operating at 56% load (inefficient)
  • Higher no-load losses
  • $3,200/year in wasted energy costs
  • Poor power factor (0.78) due to low loading

Case Study: Undersized System

Another designer used connected load but forgot diversity factors. Sized for 200 kW connected, but actual demand was 180 kW with 25% safety margin = 225 kW. Result:

  • Breaker trips during peak production
  • Voltage drops affecting equipment
  • Production downtime costs: $8,500/month

How to Calculate Demand Load Correctly #

Step 1: Inventory All Equipment #

Create a complete list with nameplate ratings:

Equipment List:
- Machine A: 20 kW
- Machine B: 15 kW
- Machine C: 10 kW
...
Total Connected: 150 kW

Step 2: Apply Diversity Factors #

Use industry-standard or measured diversity factors:

Equipment Type Typical Diversity Factor
Production machines (continuous) 0.75-0.85
Production machines (intermittent) 0.50-0.70
Welding equipment 0.30-0.50
Lighting 0.90-0.95
HVAC 0.70-0.85
Office equipment 0.60-0.75
Compressed air 0.80-0.90

Step 3: Calculate Weighted Power Factor #

Different equipment has different power factors. Calculate weighted average:

kVA = kW ÷ Power Factor

Total kVA = Σ (kW_i ÷ PF_i)
Weighted PF = Total kW ÷ Total kVA

Step 4: Add Safety Margin #

Design Load = Demand Load × (1 + Safety Margin)

Typical safety margins:

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

Complete Calculation Example #

Given:

  • Connected load: 200 kW
  • Diversity factor: 0.75
  • Weighted power factor: 0.85
  • Safety margin: 20%

Calculation:

Demand Load = 200 kW × 0.75 = 150 kW
Apparent Power (kVA) = 150 kW ÷ 0.85 = 176.5 kVA
Design Load = 150 kW × 1.20 = 180 kW
Design kVA = 176.5 × 1.20 = 211.8 kVA

Selected Transformer: 250 kVA (next standard size)
Selected Breaker: 300 A (211.8 kVA ÷ (√3 × 400V) = 305 A, rounded up)

Common Mistakes to Avoid #

Mistake 1: Using Connected Load for Equipment Sizing #

Error: Sizing transformer based on sum of nameplate ratings
Correct: Always use demand load with appropriate diversity factors

Mistake 2: Ignoring Diversity Factors #

Error: Assuming all equipment operates simultaneously
Correct: Apply realistic diversity factors based on operating patterns

Mistake 3: Mixing Up Terms #

Error: Using "demand load" when you mean "connected load"
Correct:

  • Connected load = nameplate sum
  • Demand load = connected × diversity
  • Design load = demand × (1 + margin)

Mistake 4: Not Accounting for Power Factor #

Error: Using kW directly for kVA sizing
Correct: Convert to kVA using weighted power factor

Engineering Best Practices #

1. Always Start with Connected Load #

Document every piece of equipment with nameplate ratings. This is your baseline.

2. Apply Realistic Diversity Factors #

Don't use generic factors. Observe actual operations:

  • Monitor peak vs. average loads
  • Review production schedules
  • Measure actual usage patterns

3. Validate with Measurements #

After installation, measure actual demand:

  • Compare calculated vs. measured
  • Adjust diversity factors if needed
  • Document for future reference

4. Consider Load Growth #

Design load should include:

  • Current demand load
  • Safety margin
  • Future expansion allowance

Integration with Factory Load Calculator #

Our Factory Load Calculator automatically handles the conversion from connected load to demand load. Simply enter:

  • Number of devices
  • Load per device (nameplate rating)
  • System voltage and power factor

The calculator applies appropriate diversity factors and safety margins to give you the correct demand load and equipment sizing recommendations.

Try it now: Calculate your factory load

Conclusion #

Understanding the difference between connected load and demand load is fundamental to proper electrical system design. Connected load is the theoretical maximum—useful for documentation but not for sizing. Demand load is the realistic requirement—this is what you size equipment for. The difference can be 30-40%, which translates to significant cost savings and better system efficiency. Always calculate both, but design for demand load with appropriate safety margins.