General Lighting Load Calculation

Oct 13, 2025 by miodeya.com 98 views

Introduction

When designing and installing electrical systems in residential buildings, it is essential to calculate the general lighting load accurately. This load is a critical component of the total electrical load of a dwelling and plays a significant role in determining the size of the electrical service and the number of branch circuits required. In this article, we will discuss the general lighting load of a 1,000 sq. ft. dwelling and the minimum number of small-appliance branch circuits and laundry circuits required.

General Lighting Load Calculation

The general lighting load is calculated using the National Electric Code (NEC) formula, which is as follows:

For general lighting, the load is calculated as 3 volts x amps (VA) per square foot of floor area.
For residential buildings, the general lighting load is typically calculated at 3 VA per square foot.

Using this formula, we can calculate the general lighting load of a 1,000 sq. ft. dwelling as follows:

3 VA/sq. ft. x 1,000 sq. ft. = 3,000 VA

Minimum Number of Small-Appliance Branch Circuits

The NEC requires that each dwelling have at least one small-appliance branch circuit (SABC) to serve the kitchen and other areas where small appliances are used. The minimum number of SABCs required is determined by the total number of 20-ampere receptacles required in the dwelling.

For a 1,000 sq. ft. dwelling, the minimum number of 20-ampere receptacles required is 6.
Therefore, the minimum number of SABCs required is 2, with each circuit serving 3 receptacles.

Minimum Number of Laundry Circuits

The NEC requires that each dwelling have at least one laundry circuit to serve the laundry area. The minimum number of laundry circuits required is determined by the total number of 20-ampere receptacles required in the laundry area.

For a 1,000 sq. ft. dwelling, the minimum number of 20-ampere receptacles required in the laundry area is 1.
Therefore, the minimum number of laundry circuits required is 1.

Total Electrical Load

To determine the total electrical load of a 1,000 sq. ft. dwelling, we need to add the general lighting load, the load of the small-appliance branch circuits, and the load of the laundry circuit.

General lighting load: 3,000 VA
Small-appliance branch circuits: 2 x 1,440 VA = 2,880 VA
Laundry circuit: 1 x 1,440 VA = 1,440 VA
Total electrical load: 3,000 VA + 2,880 VA + 1,440 VA = 7,320 VA

Conclusion

In conclusion, the general lighting load of a 1,000 sq. ft. dwelling is 3,000 VA, and the minimum number of small-appliance branch circuits and laundry circuits required is 2 and 1, respectively. The total electrical load of the dwelling is 7,320 VA. It is essential to calculate the general lighting load accurately to ensure that the electrical service and branch circuits are properly sized to meet the electrical needs of the dwelling.

References

National Electric Code (NEC) 2020
International Residential Code (IRC) 2020

Calculating the General Lighting Load

To calculate the general lighting load, we can use the following formula:

General lighting load (VA) = 3 VA/sq. ft. x floor area (sq. ft.)

Using this formula, we can calculate the general lighting load of a 1,000 sq. ft. dwelling as follows:

General lighting load (VA) = 3 VA/sq. ft. x 1,000 sq. ft. = 3,000 VA

Calculating the Load of Small-Appliance Branch Circuits

To calculate the load of small-appliance branch circuits, we need to determine the total number of 20-ampere receptacles required in the dwelling.

For a 1,000 sq. ft. dwelling, the minimum number of 20-ampere receptacles required is 6.
Therefore, the minimum number of small-appliance branch circuits required is 2, with each circuit serving 3 receptacles.

The load of each small-appliance branch circuit is calculated as follows:

Load per circuit (VA) = 3 VA/sq. ft. x 3 sq. ft. (per receptacle) x 3 receptacles (per circuit) = 1,440 VA
Total load of small-appliance branch circuits (VA) = 2 x 1,440 VA = 2,880 VA

Calculating the Load of Laundry Circuits

To calculate the load of laundry circuits, we need to determine the total number of 20-ampere receptacles required in the laundry area.

For a 1,000 sq. ft. dwelling, the minimum number of 20-ampere receptacles required in the laundry area is 1.
Therefore, the minimum number of laundry circuits required is 1.

The load of the laundry circuit is calculated as follows:

Load per circuit (VA) = 3 VA/sq. ft. x 3 sq. ft. (per receptacle) x 1 receptacle (per circuit) = 1,440 VA

Total Electrical Load

To determine the total electrical load of a 1,000 sq. ft. dwelling, we need to add the general lighting load, the load of the small-appliance branch circuits, and the load of the laundry circuit.

General lighting load (VA) = 3,000 VA
Small-appliance branch circuits (VA) = 2,880 VA
Laundry circuit (VA) = 1,440 VA
Total electrical load (VA) = 3,000 VA + 2,880 VA + 1,440 VA = 7,320 VA

Importance of Accurate Calculations

Accurate calculations of the general lighting load, small-appliance branch circuits, and laundry circuits are essential to ensure that the electrical service and branch circuits are properly sized to meet the electrical needs of the dwelling. Inaccurate calculations can lead to electrical overloads, which can cause fires and other safety hazards.

Conclusion

Introduction

In our previous article, we discussed the general lighting load of a 1,000 sq. ft. dwelling and the minimum number of small-appliance branch circuits and laundry circuits required. In this article, we will answer some frequently asked questions related to this topic.

Q: What is the general lighting load of a 1,000 sq. ft. dwelling?

A: The general lighting load of a 1,000 sq. ft. dwelling is 3,000 VA, calculated using the National Electric Code (NEC) formula: 3 VA/sq. ft. x floor area (sq. ft.).

Q: How many small-appliance branch circuits are required for a 1,000 sq. ft. dwelling?

A: The minimum number of small-appliance branch circuits required for a 1,000 sq. ft. dwelling is 2, with each circuit serving 3 receptacles.

Q: How many laundry circuits are required for a 1,000 sq. ft. dwelling?

A: The minimum number of laundry circuits required for a 1,000 sq. ft. dwelling is 1.

Q: What is the total electrical load of a 1,000 sq. ft. dwelling?

A: The total electrical load of a 1,000 sq. ft. dwelling is 7,320 VA, calculated by adding the general lighting load, the load of the small-appliance branch circuits, and the load of the laundry circuit.

Q: Why is it essential to calculate the general lighting load accurately?

A: Accurate calculations of the general lighting load are essential to ensure that the electrical service and branch circuits are properly sized to meet the electrical needs of the dwelling. Inaccurate calculations can lead to electrical overloads, which can cause fires and other safety hazards.

Q: Can I use a different formula to calculate the general lighting load?

A: No, the National Electric Code (NEC) requires that the general lighting load be calculated using the formula: 3 VA/sq. ft. x floor area (sq. ft.).

Q: Can I use a smaller size of electrical service and branch circuits?

A: No, the National Electric Code (NEC) requires that the electrical service and branch circuits be sized to meet the total electrical load of the dwelling.

Q: Can I use a different type of electrical service and branch circuits?

A: Yes, you can use different types of electrical service and branch circuits, such as 240-volt or 480-volt systems, but you must ensure that they are properly sized to meet the total electrical load of the dwelling.

Q: Who can help me with calculating the general lighting load and sizing the electrical service and branch circuits?

A: You can hire a licensed electrician or a professional engineer to help you with calculating the general lighting load and sizing the electrical service and branch circuits.

Q: What are the consequences of not calculating the general lighting load accurately?

A: The consequences of not calculating the general lighting load accurately can include electrical overloads, fires, and other safety hazards.

Q: Can I use a calculator to calculate the general lighting load?

A: Yes, you can use a calculator to calculate the general lighting load, but you must ensure that you are using the correct formula and values.

Q: Can I use a spreadsheet to calculate the general lighting load?

A: Yes, you can use a spreadsheet to calculate the general lighting load, but you must ensure that you are using the correct formula and values.

Conclusion

In conclusion, calculating the general lighting load of a 1,000 sq. ft. dwelling and sizing the electrical service and branch circuits is essential to ensure that the electrical needs of the dwelling are met safely and efficiently. We hope that this Q&A article has provided you with the information you need to calculate the general lighting load and size the electrical service and branch circuits correctly.