Loads and motors

Loads and motors consume electrical power. Loads represent general equipment while motors are specifically rotating machinery with special electrical characteristics.

Generic loads

Generic loads represent any electrical equipment that consumes power:

• Lighting systems
• Receptacle circuits
• HVAC equipment (non-motor)
• Electronic equipment
• Resistive heating
• Static loads

Use the generic load component when equipment is not a motor or when modeling aggregate loads.

Motors

Motors convert electrical power to mechanical rotation:

• Pumps
• Fans
• Compressors
• Conveyors
• Machine tools
• Any rotating equipment

Motors have special electrical characteristics (starting current, power factor, efficiency) that affect sizing and protection.

Creating loads and motors

1. Drag Load or Motor from component toolbar.
2. Drop on canvas.
3. Connect top handle to upstream bus or protection device.
4. Configure power consumption in edit panel.

Load types and characteristics

Load type affects how load behaves during voltage changes:

Constant power:

• Power remains constant regardless of voltage
• Most electronic equipment
• Default assumption for general loads

Constant impedance:

• Power varies with voltage squared (P ∝ V²)
• Resistive heating elements
• Incandescent lighting

Constant current:

• Power varies linearly with voltage (P ∝ V)
• Some motor loads

Select constant power unless you have specific information about load characteristics.

Load factor

The load_factor field scales the load's power consumption for analysis purposes. A load factor of 0.8 means the load operates at 80% of its rated power during power flow analysis. This is useful for modeling typical operating conditions where equipment does not run at full nameplate rating.

Set load factor to 1.0 for worst-case (full load) analysis, or a lower value to represent typical demand conditions.

Active power and reactive power

Loads consume both real power (MW or kW) and reactive power (MVAR or kVAR):

Active power (real power):

• Performs useful work
• Measured in megawatts (MW) or kilowatts (kW)
• Converted to heat, light, or mechanical energy
• Specify based on nameplate or load calculation

Reactive power:

• Magnetizing current for inductive loads
• Measured in MVAR or kVAR
• Required for motors and transformers
• Calculate from active power and power factor:

  Q = P × tan(arccos(PF))

Alternatively, specify power factor and system calculates reactive power automatically.

Rated current field

Rated Current is a design input current (connected/nameplate-style), not solved running current from power flow.

• If you edit Rated Current, the form recalculates active/reactive power from voltage and power factor.
• If you edit active power, voltage, or power factor, the form recalculates Rated Current.
• Cable auto-sizing uses ratedCurrent when it is provided.
• Standard OCPD auto-sizing currently derives current from active power, voltage, and power factor.

Power factor configuration

Power factor (PF) relates real power to apparent power:

Power Factor = Active Power / Apparent Power
PF = kW / kVA

Typical power factors:

Lagging power factor (0.8-0.95) is most common for industrial loads with motors and transformers.

Motor-specific settings

Horsepower or kW rating:

• Mechanical output power
• Nameplate rating
• Example: 50 HP, 75 HP, 100 HP
• SI equivalent: 1 HP ≈ 0.746 kW

Full-load current (FLC):

• Current drawn at rated horsepower
• From NEC tables 430.248 (1-phase) or 430.250 (3-phase)
• Used for conductor and OCPD sizing

Power factor:

• Typical range: 0.80-0.88 for induction motors
• Lower at partial load
• Set based on manufacturer data or use 0.85 default

Efficiency:

• Mechanical output / Electrical input
• Typical range: 0.88-0.95 for modern motors
• Higher for larger motors
• Premium efficiency motors: 0.93-0.96

Locked rotor current (LRA):

• Starting current (first instant of starting)
• Typically 5-8× full-load current
• Used for starting analysis
• Calculated from FLC if not specified

Motor starting methods

Direct-on-line (DOL):

• Full voltage applied at start
• Highest starting current (6-8× FLC)
• Simplest and most common
• Used for motors <50 HP on stiff systems

Star-delta (wye-delta):

• Starts in wye, transitions to delta
• Reduces starting current to ~33% of DOL
• Common for 50-200 HP motors

Soft starter:

• Electronic voltage ramping
• Adjustable starting current
• Smooth acceleration

Variable frequency drive (VFD):

• Frequency and voltage control
• Lowest starting current
• Speed control capability
• Highest cost

Starting method affects conductor sizing and protection device selection.

Motor protection and sizing

Motors require special NEC sizing rules:

Conductor sizing:

• 125% of motor FLC per NEC 430.22
• See OCPD sizing

Branch circuit protection:

• 2.5× FLC for inverse time breakers
• 1.75× FLC for time-delay fuses
• See OCPD sizing

Overload protection:

• 115-125% of motor FLC
• Separate from branch circuit protection
• Protects motor from overheating

Load annotations

After power flow, loads and motors show:

Current:

• Actual current drawn
• Compared to rated current for motors

Power:

• Active power (MW or kW)
• Reactive power (MVAR or kVAR)

Terminal voltage:

• Actual voltage at load connection
• Color-coded if too low (<95%) or too high (>105%)

Low terminal voltage causes motors to overheat and fail to develop rated torque.

Voltage rating

Specify nominal equipment voltage:

Equipment can typically operate ±10% of rated voltage, but performance degrades outside ±5%.

Related topics

• Power flow analysis - Load power calculations
• OCPD sizing - Motor protection device sizing
• Buses - Connecting loads to distribution buses