Non-Dwelling Buildings Load Calculations- Part One

In course " EE-1: Beginners' Electrical design course which is a preparation for beginners in electrical design, I explained the Electrical design philosophy for all building types and indicated the different types of buildings according to usage which were:

1. Industrial buildings
2. Commercial buildings
3. Residential buildings
4. Agricultural buildings
5. Educational buildings
6. Transportation buildings
7. Religious buildings
8. Parking and storage
9. Military buildings
10. Governmental buildings
11. Cultural buildings
12. Other buildings

In the current course" EE-3: Basic Electrical design course – Level II
", in Sixteen Articles, I explained the design of the Dwelling type buildings; I explained Where and how to distribute each type of load in a dwelling unit as per NEC code and how to calculate its Demand load for feeder and service sizing calculations, and finally I summarize the steps of calculating electrical load for any dwelling unit as per NEC standard & Optional Calculation methods in two Excel sheets/calculator.

These Sixteen Articles for the electrical design of dwelling buildings are as follows:

Today, I will begin explaining the electrical design of Non-Dwelling Buildings as per NEC Code.

List of ordinary Non-Dwelling Buildings Loads:

Most of Non-Dwelling Buildings will have the following types of loads:

Again, but for above Non-Dwelling Buildings Loads, I will explain the following points:

• Where and how to distribute each type of load in a dwelling unit as per NEC code?
• How to calculate its Demand load for feeder and service sizing calculations?

 Important!!! All design Calculations for Non-dwelling Buildings will be as per NEC standard calculation method but I will explain design calculations as per NEC Optional calculation method only for the following Non-Dwelling buildings as permitted by NEC, Part IV. Optional Feeder and Service Load Calculations: Schools  Existing Installations  New Restaurants

1- Lighting branch circuit ratings in non-dwelling units

Lighting branch circuit ratings in non-dwelling units may have one of the following ratings according to the type and application used as follows:

a) 15- and 20-Ampere Branch Circuits
It shall be permitted to supply lighting units or other utilization equipment, or a combination of both.

b) 30-Ampere Branch Circuits
It shall be permitted to supply fixed lighting units with heavy-duty lampholders.

c) 40- and 50-Ampere Branch Circuits
It shall be permitted to supply fixed lighting units with heavy-duty lampholders.

In the broad sense, lighting loads for Non-Dwelling buildings may be categorized as follows:

1. General lighting.
2. Show-window lighting.
3. Track lighting.
4. Sign and outline lighting.
5. Other lighting.

2.1 General lighting

 Definition: General lighting outlets are those Outlets intended for general use for fixed-in-place luminaires (lighting fixtures). They are only used for lighting for the normal use of the occupants and Its intensity should be adequate for any type of work performed in the area.

 Important!!! The following Lighting fixtures are not included in General Lighting category: Specialized task lighting (Show-window lighting, Track lighting, accent, specialty, or display lighting). Any special lighting for workshops, photography labs, or studios that may be located in the dwelling.

2.1.a Calculation Method

Determining the general lighting load as per NEC will be based on the load per area method as follows:

Step#1: determine the general lighting load density (in VA/ft2) for the building occupancy under design.

 Rule#1: Applying Table 220.12 The NEC code introduces minimum general lighting loads (in VA/ft2) for various types of buildings in Table 220.12. Within the same building, there are normally several different types of areas like storage, office, hallways, and cafeterias, these areas must be considered separately if their (VA/ft2) values are available in table 220.12.

Step#2: calculate the floor area in (ft2)

 Rule#2: Applying Table 220.12 The floor area for each floor shall be calculated from the outside dimensions of the building, or other area involved. The calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use (like some attics, cellars, and crawl spaces).

Step#3: calculate the general lighting load

The general lighting load is calculated by multiplying the floor area in (ft2) of a building by its unit load (in VA/ft2) derived from table 220.12.
General lighting load in (VA) = Area of Occupancy in (ft2) X general lighting load density in (VA/ft2)

Step#4: Apply lighting demand factor from table 220.42 for type of building under design.

 Important!!! The demand factors of table 220.42 shall not apply to the calculated load of feeders or services supplying areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms.

 Important!!! For the purpose of determining the circuit requirements, If the General Lighting load is continuous (as in Most commercial structures), the calculated load is multiplied by 1.25 (the inverse of 80%).

 Rule#3: Calculating Lighting Outlets load for heavy-duty Lampholders   As per NEC section 210.21, If there is Lighting Outlets for heavy-duty Lampholders in the Non-Dwelling Building, It shall be calculated at a minimum of 600 volt-amperes.

Example#1:

A 25,000 ft2 office building is being designed. What is the general lighting load and what load does the circuit need to supply?

Solution:

From Table 220.12, the unit load for an office building is 3.5 VA/ft2.

The general lighting load is determined by multiplying this value by the square footage of the building:

3.5 VA/ft2 x 25,000 ft2 = 87,500 VA
So, the general lighting load is 87,500 volt-amperes.

However, the load is continuous and can only be 80% of the load supplied by the circuit. This value must be multiplied by 1.25 to determine the circuit requirements:

87,500 VA x 1.25 = 109,375 VA

The circuit is designed to supply 109.375 KVA

Notes for table 220.12

 Important!!! Don’t apply the values of table 220.12 before reviewing the following notes: The unit values herein are based on minimum load conditions and 100 percent power factor (i.e. Load in VA = Load in Watt) and may not provide sufficient lighting for the installation contemplated. So, the designer can choose a higher value based on the existing design conditions. Under any conditions, don’t use values less than that specified in table 220.12, there are no exceptions.

 Important!!! The general lighting load unit values specified in table 220.12 for guest rooms or guest suites of hotels and motels includes the following loads: All general-use receptacle outlets of 20-ampere rating or less, including receptacles connected to Bathroom Branch Circuits, The outdoor receptacle outlets, general-use receptacle Outlets used in Basements, Garages, and Accessory Buildings. Wall lighting outlet used in Habitable Rooms, Wall lighting outlets used in hallways, stairways, attached garages, and detached garages, Wall lighting outlet used in Storage or Equipment Spaces (like attics, under-floor spaces, utility rooms, and basements), Wall lighting outlet used in Guest Rooms or Guest Suites In hotels, motels, or similar occupancies. So, no need to add the above outlets in load calculations per NEC method.

 Important!!! The NEC method and table 220.12 are applied for any Additions to Existing Installations for non-dwelling installations.

 Important!!! Energy saving–type calculations (which used to reduce the connected lighting load and actual power consumption) are not permitted to be used to determine the minimum calculated lighting load if they produce loads less than the load calculated according to 220.12.

2.1.b Notes for NEC method for calculation of lighting branch circuit load

 Important!!! The NEC doesn’t introduce a procedure for calculating the actual full load for the individual lighting fixtures in a general lighting branch circuit.

 Rule#4: NEC method for calculation of lighting branch circuit load If the required information for calculating the actual full load for every individual lighting fixture in the circuit is available, the following procedure will be applied: Calculate the actual load for the lighting branch circuit by summing of actual full load for its individual lighting fixtures.  Compare the values obtained from NEC method with that obtained from actual load method and select the greater load value to be used in the design.

 Important!!! Actually, The NEC method for calculation of lighting load is not required if the actual full load for every individual lighting fixture in the circuit is determined. Methods for determining the actual full load for every individual lighting fixture in the circuit is explained in our course and I recommend reviewing these methods very well.

 Rule#5: determining the actual load current of circuits supplying lighting units that have ballasts, transformers, autotransformers, or LED drivers As per NEC Section 220.18 (b) states , circuits supplying lighting units that have ballasts, transformers, autotransformers, or LED drivers, the calculated load shall be based on the total ampere ratings of such units and not on the total watts of the lamps. This means that the losses in light fixture switchgear (ballast, internal wiring, etc.) must be taken into account when calculating the actual full load of light fixtures and the current rating of the ballast, not the tube wattage, will be used.

Example#2:

A fluorescent lighting fixtures with 4 numbers 2 feet lamps, 18 watt/ lamp.
Calculate the actual load for this lighting fixture.

Solution:
The actual total load of fixture = 4 lamps x 18 watt/lamp + losses

So, we can’t know the actual losses, we will use the same equation in another form

The actual total load of fixture = 4 ballast x watt/ballast = 4 x 20 w = 80 watt

2.2 Show-window lighting

The calculation of this type of lighting is explained in Article "
".

2.3 Track lighting

The calculation of this type of lighting is explained in Article
Branch Circuit Design Calculations – Part Four ".

2.4 Sign and outline lighting

The calculation of this type of lighting is explained in Article "
Branch Circuit Design Calculations – Part Five ".

2.5 Other lighting

Other lighting includes but not limited to the following:

1. Security lighting,
2. Parking area lighting,
3. Sidewalk lighting,
6. Tunnel Lighting.

2.5.a Rules applied for Calculation of Other lighting loads

Unfortunately, The NEC code don’t provide calculation rules for lighting types included under these additional lighting loads.
So, all additional lighting loads are calculated using the actual load designed by professional lighting programs and methods as explained in our course.

 Don’t forget… These additional lighting loads are considered continuous loads where appropriate and must be multiplied by 1.25 for feeder and overcurrent protection calculations.

 Rule#6: Calculating the total lighting load for buildings having more than one lighting category. lighting loads for Non-Dwelling buildings may be categorized as follows: General lighting. Show-window lighting. Track lighting. Sign and outline lighting. Other lighting. If more than one of the above lighting categories is existing in the same building, Each lighting Category load is computed separately and then combined to other lighting categories load to determine the total lighting load.

In the next article, I will explain design calculations for Receptacle Loads for Non-Dwelling Buildings. Please, keep following.