Article 220—Load Calculations:
220.43 Show-Window and Track Lighting
The purpose of the National Electrical Code (NEC) is the practical safeguarding of people and property from hazards arising from the use of electricity [90.1(A)]. The NEC is divided into an introduction, nine chapters and annexes. Provisions in the introduction (Article 90) include Purpose, Scope, Code Arrangement, Enforcement, Rules (Mandatory and Permissive), Explanatory Material, Formal Interpretations, Examination of Equipment for Safety, Wiring Planning, and Units of Measurement.
While chapters 1 through 4 apply generally, chapters 5 through 7 apply to special occupancies, special equipment or other special conditions. Requirements in chapters 5, 6 and 7 supplement or modify the general rules. Communications systems are covered in chapter 8, and miscellaneous tables are in chapter 9. Requirements for calculating branch-circuit, feeder and service loads are in Article 220 of the NEC. Five parts make up Article 220. Part I contains general requirements for calculation methods. Part II includes methods for calculating branch circuits. Feeder and service calculation provisions are in Part III. Part IV covers optional feeder and service-load calculation specifications. Farm-load calculation requirements are in Part V. Last month’s Code in Focus concluded by covering general lighting load demand factors in 220.42 and Table 220.42.
This month, the discussion continues with show windows and track lighting as specified in 220.43.
A show window, as defined in Article 100, is any window designed or used to display goods or advertising material. Show windows can be enclosed (partially or fully) or entirely open at the rear. Whether or not it has a platform raised higher than the street floor level is not a consideration when defining a show window (see Figure 1). This is the second time show windows have been mentioned in Article 220. While branch-circuits supplying show windows must be calculated in accordance with 220.14(G), show-window lighting loads on feeders and services must be calculated in accordance with 220.43(A). Branch circuits supplying show windows were covered in part V of this series.
While there are two methods for calculating branch circuits supplying show windows, there is only one method for calculating show windows on feeders and services. For show-window lighting, a minimum load of 200 volt-amperes per linear foot (660 volt-amperes per linear meter) must be included for each show window [220.43(A)]. For example, what is the calculated service load for a show window measuring 14 feet? Multiply 200 volt-amperes by 14 feet (200 × 14 = 2,800). The calculated load for the service must include at least 2,800 volt-amperes because of the 14 feet of show window.
All show windows, regardless of size, must be included. The measurement must be taken horizontally along the base of the show window. For example, a retail store has an accordion-like or zigzag show window. The show window is made up of six individual windows; each window is 2 feet wide. The distance across the floor of the show-window area is only 10 feet. What load must be included for this show-window lighting when calculating the service? Although the distance across the floor is only 10 feet, do not use this measurement. The measurement must be taken horizontally along the base of the show window. The sum of six show windows measuring 2 feet each is 12 feet. Multiply 200 volt-amperes by 12 feet (200 × 12 = 2,400). This service calculation must include a load of not less than 2,400 volt-amperes for 12 feet of show window.
Because show-window lighting is a load where the maximum current is expected to continue for three hours or more, it is a continuous load. When sizing conductors and overcurrent protection for feeders and services, continuous loads must be calculated at 125 percent. For example, a small store has a corner show window. The front window is 6 feet wide and the side window is 4 feet wide. How much load will this show window add to the service-entrance conductor calculation? Service-entrance conductors must be sized in accordance with 230.42(A). Feeder conductors must be sized in accordance with 215.2. First multiply total show-window dimension (6 + 4 = 10 feet) by 200 volt-amperes per linear foot (10 × 200 = 2,000). Because this is a continuous load, multiply 2,000 volt-amperes by 125 percent (2,000 × 125% = 2,500). The minimum load required for this show window when sizing service-entrance conductors is 2,500 volt-amperes (Note: See 215.3 for feeder overcurrent protection and 230.90 for service overcurrent protection).
When calculating feeder and service loads, track lighting is not included as part of the general lighting load specified in 220.12 and Table 220.12. Depending on the occupancy, an additional load of 150 volt-amperes may be required for every 2 feet (600 mm) of lighting track or fraction thereof [220.43(B)]. For example, a retail store will have 150 feet of track lighting. What is the calculated load? Start by dividing the length of track by 2 feet (150 ÷ 2 = 75). Next, multiply 75 by 150 volt-amperes (75 × 150 = 11,250). The minimum calculated load for a store with 150 feet of track lighting is 11,250 volt-amperes.
In a store, track lighting will be energized for more than three hours and therefore is a continuous load. When sizing overcurrent protection (or conductors) for feeders and services, multiply the track-lighting load by 125 percent.
If track lighting is installed, the additional track-lighting load is required unless the occupancies are dwelling units, guest rooms or guest suites of hotels or motels. For example, 28 feet of track lighting is shown on the floor plans of a one-family dwelling. How much additional load will this track lighting add to the service? In accordance with 220.43(B), no additional load is required for track lighting installed in a dwelling unit.
Where multicircuit track is installed, the load shall be considered to be divided equally between the track circuits [220.43(B)]. No additional load is required for multicircuit track; simply divide the calculated load by the number of circuits in the track.
Next month’s Code in Focus continues the discussion of load calculations. EC
MILLER owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615.333.3336, charles@charlesRmiller.com, or www.charlesRmiller.com.