Commercial Load Calculator

Related tools: Feeder Load Calculator, Continuous Load Calculator, and Appliance Load Calculator.

A commercial load calculator converts user-defined load blocks into an adjusted load in VA and an estimated line current in amperes. The result supports preliminary feeder, service, panel, transformer, and equipment-capacity review when connected load, demand assumptions, continuous loading treatment, system voltage, and phase configuration are already known.

The calculator produces these primary values:

• Connected load — total installed nameplate or calculated VA entered across all load blocks
• Demand load — connected load after the entered demand factor for each block
• Continuous adder — additional VA created by the entered continuous multiplier
• Adjusted load — demand load plus the continuous adder
• Line current — estimated load current at the selected voltage and phase arrangement
• Entered capacity margin — difference between the entered ampere value and calculated line current

The resulting current is commonly carried into conductor ampacity review, feeder sizing, overcurrent-protection coordination, panel capacity review, transformer loading, and voltage-drop calculations. It does not select an AWG or kcmil conductor size, determine raceway fill, calculate voltage drop, or establish an NEC-compliant service or feeder rating by itself.

Load Blocks and Demand Assumptions

Each load category is entered as a separate load block. The available fields are:

Field	Electrical use
Label	Identifies the load group, such as Lighting, Receptacles, HVAC, Equipment, or a tenant-specific load category
Connected load (VA)	Total apparent load assigned to that block before demand or continuous-load treatment
Demand factor (%)	User-entered percentage applied to the connected VA for that block
Continuous multiplier (%)	User-entered multiplier applied after the demand factor
System voltage (V)	Voltage used to convert adjusted VA to line current
Phase	Selects single-phase or balanced three-phase current mathematics
Entered capacity (A)	Optional feeder, service, breaker, panel, or equipment ampere value used only for comparison

A load block allows lighting, receptacles, HVAC, process equipment, and other loads to retain separate demand assumptions. That is useful when preliminary design information comes from tenant schedules, equipment nameplates, design narratives, owner load projections, or engineering load summaries.

The Demand factor (%) and Continuous multiplier (%) are user assumptions. They are not automatic code-table lookups, occupancy classifications, or equipment-specific determinations. Any NEC demand treatment, continuous-load requirement, motor treatment, noncoincident-load analysis, or special occupancy rule must be established separately before those values are entered.

Demand Load and Continuous Adder

For each row, the calculator first applies the entered demand factor:

\(\displaystyle \text{Demand VA}_i = \text{Connected Load VA}_i \times \frac{\text{Demand Factor}_i}{100}\)

It then applies the continuous multiplier to the demand-adjusted load:

\(\displaystyle \text{Adjusted VA}_i = \text{Demand VA}_i \times \frac{\text{Continuous Multiplier}_i}{100}\)

The calculator totals the individual rows:

\(\displaystyle \text{Connected Load} = \sum \text{Connected Load VA}_i\)

\(\displaystyle \text{Demand Load} = \sum \text{Demand VA}_i\)

\(\displaystyle \text{Adjusted Load} = \sum \text{Adjusted VA}_i\)

The displayed Continuous adder is the difference between adjusted load and demand load:

\(\displaystyle \text{Continuous Adder} = \text{Adjusted Load} - \text{Demand Load}\)

A 125% continuous multiplier does not add 125% of the load. It changes a demand-adjusted load to 125% of itself, creating a 25% adder. For example, a 12,000 VA lighting block at 100% demand with a 125% continuous multiplier contributes 12,000 VA to demand load and 15,000 VA to adjusted load. Its continuous adder is 3,000 VA.

The displayed Effective demand factor compares the final adjusted load to the total connected load:

\(\displaystyle \text{Effective Demand Factor} = \frac{\text{Adjusted Load}}{\text{Connected Load}} \times 100\)

Because continuous multipliers are applied after demand factors, the effective demand factor can differ from a simple average of the row-level demand factors.

Line Current at System Voltage

The calculator converts the adjusted VA to line current using the selected voltage and phase arrangement.

For single-phase systems:

\(\displaystyle \text{Line Current} = \frac{\text{Adjusted Load VA}}{\text{System Voltage V}}\)

For balanced three-phase systems:

\(\displaystyle \text{Line Current} = \frac{\text{Adjusted Load VA}} {\sqrt{3} \times \text{System Voltage V}}\)

The balanced three-phase selection uses a phase multiplier of approximately 1.7321:

\(\displaystyle \sqrt{3} \approx 1.7321\)

This calculation assumes the adjusted load is distributed evenly among the three phases. It estimates line current; it does not evaluate phase imbalance, neutral loading, harmonic current, separately derived systems, power factor, or the actual operating profile of nonlinear equipment.

For conductor sizing, the calculated current must still be evaluated against the applicable conductor ampacity, terminal rating, insulation temperature rating, ambient-temperature correction factor, adjustment factor for current-carrying conductors, and equipment limitations. A line-current result alone does not establish the permitted ampacity of a feeder conductor.

Calculation Example

The following commercial load example uses four load blocks on a 480 V balanced three-phase system with an Entered capacity (A) of 100 A.

Label	Connected load (VA)	Demand factor (%)	Continuous multiplier (%)	Demand VA	Adjusted VA
Lighting	12,000	100	125	12,000	15,000
Receptacles	18,000	80	100	14,400	14,400
HVAC	24,000	100	100	24,000	24,000
Equipment	15,000	75	100	11,250	11,250
Total	69,000	—	—	61,650	64,650

The results are:

• Connected load: 69,000 VA
• Demand load: 61,650 VA
• Continuous adder: 3,000 VA
• Adjusted load: 64,650 VA
• Phase multiplier: 1.7321 x
• Line current: 77.7619 A
• Entered capacity margin: 22.2381 A
• Effective demand factor: 93.6957%
• Counted load blocks: 4 blocks

The line-current calculation is:

\(\displaystyle \text{Line Current} = \frac{64{,}650} {1.7321 \times 480} = 77.7619 \text{ A}\)

The capacity comparison is:

\(\displaystyle \text{Entered Capacity Margin} = 100 \text{ A} - 77.7619 \text{ A} = 22.2381 \text{ A}\)

In this example, the entered 100 A comparison value exceeds the calculated balanced three-phase line current by 22.2381 A. That comparison does not confirm that a 100 A feeder, breaker, disconnect, panel bus, transformer secondary, or conductor set is acceptable. The final design must account for conductor ampacity, terminal limitations, overcurrent protection, available fault current, equipment listings, and the actual electrical distribution arrangement.

Feeder and Service Review Limits

The calculator is intended for preliminary commercial load arithmetic. It does not perform occupancy classification, demand-table selection, feeder selection, service sizing, utility review, or code-compliance verification.

Verify the following separately when the calculated load is used for a field or design decision:

• Applicable NEC load-calculation requirements and local AHJ amendments
• Correct classification of continuous and noncontinuous loads
• Motor loads, including any required largest-motor or motor-feeder treatment
• HVAC load relationships, noncoincident loads, and equipment operating sequences
• Actual voltage and phase configuration at the load point
• Balanced versus unbalanced phase loading and neutral-conductor requirements
• Conductor ampacity after terminal rating, insulation temperature rating, ambient correction, and current-carrying-conductor adjustment
• OCPD rating, equipment bus rating, disconnect rating, and panelboard limitations
• Voltage drop on long branch circuits and feeders
• Raceway fill, conductor quantity, bending space, and installation conditions

Use the calculated Adjusted load and Line current as organized starting values for the next electrical design check, not as a final conductor, breaker, feeder, or service selection.