Commercial Office Load Calculator

A commercial office load calculator converts entered office loads in volt-amperes (VA) into an adjusted load and estimated line current. The result supports preliminary feeder and branch-circuit load review, panel loading, raceway planning, conductor ampacity evaluation, and voltage-drop calculations.

Office tenant loads commonly combine lighting, receptacle loads, workstation equipment, server or communications equipment, HVAC controls, dedicated equipment, and other connected utilization loads. These loads do not always operate at full connected load simultaneously, and some may require continuous-load treatment. This worksheet applies the demand factor and continuous multiplier entered for each load row before converting the combined adjusted VA to amperes.

The calculator reports:

• Connected load — Total nameplate or assigned VA entered across all office load rows
• Demand load — Total VA after each row’s entered Demand factor (%)
• Continuous adder — The additional VA created when a row’s Continuous multiplier (%) exceeds 100%
• Adjusted load — Final VA after demand and continuous-load multipliers
• Line current — Calculated current at the entered System voltage (V) and Phase model
• Load row count — Number of office load rows included
• Phase multiplier — The conversion factor used for the selected phase arrangement

For a three-phase office distribution system, line current is generally the number carried forward into preliminary conductor, overcurrent-device, panelboard, feeder, and voltage-drop review.

Related office load tools: Commercial Load Calculator, Continuous Load Calculator, and Feeder Load Calculator.

Load Row Arithmetic

Each Office load rows entry contains three electrical inputs:

Field	Electrical use
Load label	Identifies the connected office load or load group
Connected load (VA)	Entered apparent power for that row
Demand factor (%)	Percentage of connected VA carried into the demand calculation
Continuous multiplier (%)	Multiplier applied after demand adjustment to account for continuous loading treatment

The worksheet applies the entered percentages independently to each row. For an individual row:

\(\displaystyle \text{Demand VA} = \text{Connected load (VA)} \times \frac{\text{Demand factor (\%)}}{100}\)

\(\displaystyle \text{Adjusted row VA} = \text{Demand VA} \times \frac{\text{Continuous multiplier (\%)}}{100}\)

The Continuous adder is the difference between adjusted VA and demand VA:

\(\displaystyle \text{Continuous adder} = \text{Adjusted row VA} - \text{Demand VA}\)

For all entered rows:

\(\displaystyle \text{Connected load} = \sum \text{Connected row VA}\)

\(\displaystyle \text{Demand load} = \sum \text{Demand row VA}\)

\(\displaystyle \text{Adjusted load} = \sum \text{Adjusted row VA}\)

A demand factor of 100% retains the entire entered connected load. A continuous multiplier of 100% adds no continuous-load increase. For example, a 125% continuous multiplier produces an additional 25% of that row’s demand load.

Three-Phase Line Current

With Phase model set to Three-phase, the calculator uses a phase multiplier of 1.7321, representing sqrt{3}.

\(\displaystyle \text{Line current (A)} = \frac{\text{Adjusted load (VA)}} {\text{System voltage (V)} \times 1.7321}\)

For a 480 V three-phase system:

\(\displaystyle \text{Line current (A)} = \frac{\text{Adjusted load (VA)}} {480 \times 1.7321}\)

The System voltage (V) must be the voltage applicable to the current conversion. A 480 V three-phase feeder and a 208 V three-phase panel can serve office-related loads but produce substantially different line-current results for the same VA load.

The result is an apparent-power current calculation. It does not independently determine real power in watts, reactive power, power factor, harmonic content, neutral current, or motor starting current.

Calculation Example

Assume a 480 V, three-phase office feeder review with the following entered rows:

Load label	Connected load (VA)	Demand factor (%)	Continuous multiplier (%)
General office lighting	18,000	100	125
Receptacle and workstation load	30,000	75	100
Communications equipment	12,000	100	125

The row calculations are:

Load label	Demand VA	Continuous adder	Adjusted VA
General office lighting	18,000 VA	4,500 VA	22,500 VA
Receptacle and workstation load	22,500 VA	0 VA	22,500 VA
Communications equipment	12,000 VA	3,000 VA	15,000 VA
Total	52,500 VA	7,500 VA	60,000 VA

The calculator outputs:

\(\displaystyle \text{Connected load} = 60{,}000 \text{VA}\)

\(\displaystyle \text{Demand load} = 52{,}500 \text{VA}\)

\(\displaystyle \text{Continuous adder} = 7{,}500 \text{VA}\)

\(\displaystyle \text{Adjusted load} = 60{,}000 \text{VA}\)

\(\displaystyle \text{Line current} = \frac{60{,}000} {480 \times 1.7321} = 72.2 \text{A}\)

The resulting 72.2 A is the calculated three-phase line current for the entered assumptions. It can be used as a starting load value when reviewing a proposed feeder conductor size, OCPD rating, panel capacity, raceway fill, and voltage-drop performance.

Conductor and Raceway Review

The calculated line current is not itself a conductor size. Conductor selection requires a separate ampacity determination based on the actual installation.

A feeder review commonly considers:

• Conductor material and size in AWG or kcmil
• Insulation temperature rating
• Terminal rating and equipment listing limits
• Ambient-temperature correction factor
• Adjustment factor for current-carrying conductors
• Number of current-carrying conductors in the raceway or cable
• Overcurrent protective device rating and coordination
• Feeder versus branch-circuit application
• Equipment grounding conductor requirements
• Raceway fill and physical conductor arrangement
• Calculated voltage drop over the actual conductor length

The calculated adjusted load can be compared with available conductor ampacity only after applicable correction and adjustment factors are determined. A conductor’s insulation rating does not automatically establish the usable ampacity at equipment terminations; the applicable terminal rating and installation conditions must also be verified.

For a long office feeder, voltage drop may become a practical design constraint even when the conductor has sufficient ampacity. The calculator supplies the load current used in a separate voltage-drop calculation, but it does not include conductor length, impedance, conductor material, conductor size, or power factor.

Field Verification

The worksheet keeps the office context attached to shared commercial load arithmetic. It does not perform occupancy classification, load-table selection, feeder selection, service sizing, panelboard evaluation, or authority determination.

Verify the source and applicability of every entered Demand factor (%) and Continuous multiplier (%) before relying on the result for design or permitting. Confirm the actual connected equipment, voltage, phase arrangement, continuous operating characteristics, motor and HVAC loads, noncoincident loads, existing load conditions, and manufacturer requirements.

Final conductor, OCPD, raceway, and service decisions require the applicable electrical code, adopted local amendments, project documents, equipment ratings, and AHJ requirements.