You're on the right track! Let's break down the differences between NEC 2023 Sections 220.42, 220.45, and 220.47

220.42 General Lighting Loads
Scope

This section applies to calculating the general lighting load for all occupancies. It's the starting point for determining the minimum lighting load for any building or portion thereof.

Key Principle

Uses Volt-Amperes per Square Foot (VA/sq ft) values based on the occupancy type. The table in 220.12 provides these VA/sq ft values (e.g., dwelling units, office buildings, schools, warehouses).

Applies To

Everything. If you are doing a load calculation, you start here to get the general lighting load, regardless of whether it's commercial, residential, or industrial.

Important Notes

The calculated load from this section is the minimum required. If the actual connected lighting load is higher, you must use the actual connected load. Modifications as permitted elsewhere in the code, such as Article 230.

220.45 General Illumination - Dwelling Units. Scope

This section is used for calculating the general illumination load for the dwelling unit.

Key Principle

Uses Volt-Amperes per Square Foot (VA/sq ft) values based on the occupancy type. The table in 220.12 provides these VA/sq ft values (e.g., dwelling units, office buildings, schools, warehouses).

Applies To

Dwelling units only. If you are doing a load calculation for a dwelling unit, you use this section after 220.42.

Important Notes

Provides exceptions, which should be referred to as they can affect the final load.

220.47 Receptacle Outlets Scope

This section addresses the calculation of receptacle loads (other than those for general illumination or appliance outlets specifically addressed elsewhere) in non-dwelling unit occupancies. It focuses on commercial and industrial settings.

Key Principle

This is usually calculated using 180 VA per outlet, or as determined by manufacturer's specification.

Applies To

Non-dwelling unit occupancies (commercial and industrial) where you need to determine the load contribution of general-purpose receptacles.

Important Notes

Exceptions in 220.14 may allow you to use demand factors on these loads in certain situations. Doesn't include receptacles for specific appliances or lighting, which are handled elsewhere (e.g., 220.18 for show windows). This section specifically excludes dwelling unit receptacles. Dwelling unit receptacles (other than those for specific appliances) are generally covered under the general lighting load calculation (220.12 and 220.42).

In Summary



220.42 (General Lighting Loads)

The foundation. Determines the minimum general lighting load for all occupancies, using VA/sq ft values from 220.12.

220.45 (General Illumination - Dwelling Units)

Specific for dwelling units, and allows for exceptions that may affect the final load.

220.47 (Receptacle Outlets)

Focuses on receptacle loads (excluding specific appliance or lighting outlets) in non-dwelling unit* occupancies, typically using 180 VA per outlet, unless the receptacle load is specifically accounted for elsewhere.Think of it this way:1.

220.42 is the universal starting point for lighting.2. 220.45 is more specific and applies to the lighting of a dwelling unit.3. 220.47 is used for the receptacle load of commercial and industrial spaces.Always refer to the actual NEC document for the most accurate and up-to-date information, and consult with a qualified electrical professional for specific project requirements. These sections are interconnected, and proper understanding is crucial for accurate load calculations and safe electrical installations. Flag for review