CHAPTER 3 - ELECTRICAL LOAD REQUIREMENTS

As a Construction Electrician first class, you may be required to provide electrical service to various types of facilities. The material presented in this chapter is based on the 1990 National Electrical CodeR (NECR)1 and addresses requirements in the installation of an industrial feeder system for dwelling units and industrial areas, the function and the correct steps for operation and installation of ground fault interrupter circuit breakers, and restrictions placed on electrical systems installed in hazardous locations. Upon completion of this chapter, you will be able to (1) compute electrical load requirements and (2) provide safe electrical service to the load.

SINGLE-FAMILY DWELLING

Performing the calculations to provide electrical power to a dwelling can be divided into two phases. Phase I is determining the number and size of branch circuits required to serve the load. Phase II is calculating the size of the serviceentrance conductor and the size of the neutral conductor.

TYPES OF DWELLING UNIT LOAD

The total load of a dwelling unit can be divided into three categories: general lighting load, small appliance and laundry load, and special appliance load.

General Lighting Load

The NEC^R states that receptacle outlets rated at 20 amps or less may be used for general lighting. These receptacles may be included in the calculations for general lighting load.

¹ National Electrical Code^R and NEC^R are registered trademarks of the National Fire Protection Association, Inc., Quincy, MA 02269.

The easiest method to determine the general lighting load is to multiply the square footage of a dwelling by the volt-amperes (VA) per square foot listed in table 3-1 (NECR, table 220-3(b)). Do not include garages, carports, patios, or open porches in the square footage calculations. Multiply the outside length times the outside width times the number of floors to determine the total area. Multiply this number times 3 VA to determine the general lighting load. Use the following formulas to find the general lighting load:

Total area = outside length outside width number of floors

General lighting load = total area VA

Small Appliance and Laundry Load

In addition to the number of branch circuits determined by the general lighting load calculations, at least two 20-amp, 1,500-VA small appliance circuits must be installed in the kitchen, pantry, breakfast room, and dining room only. The load on these circuits must be distributed equally across the phases to minimize unbalanced load on the neutral.

At least one additional 20-amp, 1,500-VA branch circuit must be provided to supply the laundry load. Do not install any other receptacle outlets on this branch circuit.

The 1,500-VA rating of each branch circuit is applied to the calculations for the service-entrance conductor size. The 20-amp branch circuit rating is used to supply the small appliance and laundry loads.

The small appliance and laundry loads may be totaled and added to the general lighting load provided they meet the demand factors discussed later in this chapter.

Table 3-1.\General Lighting Loads by Occupancies

For SI units: one square foot = 0.093 square meter.

*All general use receptacle outlets of 20-ampere or less rating in one-family, two-family and

multifamily dwellings and in guest rooms of hotels and motels [except those connected to the receptacle

circuits specified in Sections 220-4(b) and (c)] shall be considered as outlets for general illumination,

and no additional load calculations shall be required for such outlets.

**In addition a unit load of 1 volt-ampere per square foot shall be included for general purpose

receptacle outlets when the actual number of general purpose receptacle outlets is unknown.

Reprinted with permission from NPFA 70-1990, the National Electrical Code^R, Copyright^c1989, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association, on the referenced subject which is represented only by the standard in its entirety.

Special Appliance Load

Any additional electrical appliances, such as ranges, hot-water heaters, air conditioners, dryers, dishwashers, and garbage disposals, must be supplied by individual branch circuits. Do not connect these appliances to the general lighting circuits. If the appliances were connected to the general lighting circuits, a fault in the appliance(s) could de-energize the lighting, creating a serious safety hazard.