Dwelling General Lighting Load Calculator

A dwelling general lighting load calculator produces the selected lighting load line item in volt-amperes (VA) for a residential load worksheet. That VA value is carried into the applicable dwelling load calculation, where it can affect service and feeder load review, conductor ampacity selection, overcurrent protection evaluation, panel capacity, and voltage-drop review.

The calculator uses either a floor-area estimate or a verified entered value. It does not establish the required VA-per-square-foot allowance. The selected basis must come from the adopted electrical requirement, AHJ worksheet, engineering record, or project documentation.

Lighting Load Basis

The residential general lighting load represents the allowance assigned to dwelling floor area under the selected worksheet method. It is a load-calculation value, not a measurement of the watts presently installed in luminaires.

For the area-based method, enter the floor area covered by the selected worksheet basis and the applicable lighting basis. For a documented alternative basis, enter the verified value as a known load and select the override method.

Input field	Purpose
Dwelling floor area (sq ft)	Floor area covered by the selected residential worksheet basis
Entered lighting basis (VA/sq ft)	VA-per-square-foot allowance taken from the adopted requirement, AHJ worksheet, or project record
Known load override (VA)	Optional verified worksheet or measured value used when the override basis is selected
Load basis	Selects either the area estimate or the verified entered override

The default value shown for Entered lighting basis (VA/sq ft) is an example only. A different adopted code edition, jurisdictional worksheet, design method, or project condition may require a different basis.

Calculation Method

When Load basis is set to Area x entered basis, the calculator multiplies floor area by the entered VA-per-square-foot value:

\(\displaystyle \text{Area-based load (VA)} = \text{Dwelling floor area (sq ft)} \times \text{Entered lighting basis (VA/sq ft)}\)

The calculator then reports that amount as the Selected lighting load line item.

When Load basis is set to the verified entered override, the calculator uses:

\(\displaystyle \text{Selected lighting load line item (VA)} = \text{Known load override (VA)}\)

The override does not add to the area-based load. It replaces the area estimate when that load basis is selected.

Calculation Example

A dwelling has 2,000 sq ft of floor area covered by the selected worksheet basis. The project worksheet calls for an entered lighting basis of 3 VA/sq ft, and no verified override is being used.

Field	Entered value
Dwelling floor area (sq ft)	2,000
Entered lighting basis (VA/sq ft)	3
Known load override (VA)	0
Load basis	Area x entered basis

\(\displaystyle 2{,}000\ \text{sq ft} \times 3\ \text{VA/sq ft} = 6{,}000\ \text{VA}\)

Area-based load: 6,000 VA Selected lighting load line item: 6,000 VA

That 6,000 VA is the residential general-lighting entry produced by this worksheet step. It may later be combined with other applicable dwelling loads and processed under the governing load-calculation method. It is not, by itself, a final feeder ampacity, breaker size, AWG or kcmil conductor size, or raceway-fill result.

Use in Service and Feeder Review

The selected lighting load line item is generally used upstream of conductor and equipment selection. After the applicable residential load calculation combines and adjusts the required load categories, the resulting calculated load may be converted to current for the system voltage and phase arrangement.

For a single-phase load calculation, the basic relationship is:

\(\displaystyle \text{Current (A)} = \frac{\text{Apparent power (VA)}}{\text{Voltage (V)}}\)

For example, converting 6,000 VA directly at 240 V yields 25 A. That conversion alone does not authorize a 25 A conductor or overcurrent device selection. Final conductor sizing must account for the completed calculated load, terminal rating, insulation temperature rating, ampacity limits, any applicable adjustment factor or correction factor, and the installed conductor method.

A lighting load worksheet line also does not determine:

• Branch-circuit conductor size or branch-circuit overcurrent protection
• Feeder conductor AWG or kcmil
• Raceway fill or conduit layout
• Number of current-carrying conductors
• Voltage-drop adequacy
• Panelboard bus rating or service-equipment rating
• Loads from appliances, HVAC equipment, motors, electric heating, EV equipment, or other separately calculated equipment

Field and Code Limits

Use floor area only to the extent the selected worksheet basis applies to that area. Do not assume that every enclosed, unfinished, accessory, altered, or mixed-use space belongs in the same dwelling floor-area entry without verifying the governing worksheet or AHJ direction.

The Known load override (VA) should be supported by a verified worksheet, measured record, engineered calculation, or other project documentation accepted for the selected method. Selecting an override changes the calculator’s arithmetic; acceptance of that override remains a code, design, and AHJ decision.

The calculator produces a single lighting-load line item in VA. Final service, feeder, branch-circuit, ampacity, voltage-drop, and installation decisions must be checked against the adopted requirements and the actual electrical installation.