Branch Circuit Design Calculations – Part Five


In the previous article in our new course 
" Branch Circuit Design Calculations – Part Two ", I listed the (5) categories of Lighting Branch circuits, which were: 

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



Also, in the previous Article 
Branch Circuit Design Calculations – Part Three ", I explained the following points: 

  1. The design calculation method for general lighting, 
  2. The calculation method for determination of the Minimum Number of General Lighting Branch Circuits in a building, 
  3. The calculation method for Determination of maximum Permissible number of lighting fixtures on a general lighting branch circuit. 

I explained how to design the show window and track lighting loads in the previous article " Branch Circuit Design Calculations – Part Four"



Today I will explain the design calculations for sign and outline lighting branch circuits as follows. 


You can review the following previous articles for more information:




4- Sign and outline lighting

4.1 Definition

Sign and Outline Lighting:
An arrangement of incandescent lamps, electric-discharge lighting, or other electrically powered light sources to outline or call attention to certain features such as the shape of a building or the decoration of a window.


Fig.1: Section Sign

Sign and outline lighting illumination systems include, but are not limited to:



  • cold cathode neon tubing,
  • high-intensity discharge lamps (HID),
  • fluorescent or incandescent lamps,
  • light-emitting diodes (LEDs),
  • electroluminescent and inductance lighting. 


Sometimes due to size restrictions or other logistical factors, the electric sign can be constructed in multiple factory-wired subassemblies (Section sign) that can be assembled at the sign-installation location. The definition for section sign will be as follows: 



Section Sign: (see fig.1)

A sign or outline lighting system, shipped as sub-assemblies that requires field-installed wiring between the sub-assemblies to complete the overall sign. The sub-assemblies are either physically joined to form a single sign unit or are installed as separate remote parts of an overall sign.




4.2 NEC rules applied for Sign and Outline lighting:



The Code includes several sections applicable to 
sign and outline lighting:

  • 220.14 (F) Sign and Outline Lighting. 
  • Article 600. 


2.3 Design calculations for Sign and Outline lighting:

A- Number of required sign and outline branch circuits



As per section 600.5 (A), At least one dedicated sign and outline branch circuit must be provided for each commercial Space at each entrance of a commercial building / occupancy accessible to pedestrians. 




Important!!!
Sometimes, the designer may assign A group of branch circuits supplied by a dedicated feeder for one sign lighting only, if  there is need for installation of a Large sign with higher loads than that specified by section 220.14 (F) in below and that usually be a multi section sign as described in the definitions in above.


Notes for section 600.5(A): 

  • The term “dedicated” in above means that the branch circuit for sign and outline lighting will not supply any other load. 
  • Service hallways or corridors shall not be considered accessible to pedestrians, no sign and outline lighting branch circuits will be added there. 
  • The loads for branch circuits of sign and outline lighting shall be added in the design stage of new commercial buildings for each commercial space as per 600.5 (A), because it is not convenient to add it later when the space is occupied or when a new occupant moves into an existing space. 



B- Sign and outline lighting branch circuit rating


As per section 600.5(B), the following rules are applied:

  • Branch circuits that supply neon tubing installations shall not be rated in excess of 30 amperes. 
  • Branch circuits that supply all other signs and outline lighting systems shall be rated not to exceed 20 amperes.


Important!!!
Large signs often have load requirements that exceed the ratings permitted by section 600.5(B) will be divided to group of branch circuits supplied by a feeder which is not limited by the rating specified in 600.5(B).


Important!!!
In some cases, particularly for signs installed along highways, a utility service dedicated to the sign is provided. The rating of the feeder or service is not limited by the rating specified in 600.5(B).



C- Load Value for sign and outline lighting


As per NEC section 220.14 (F) , Sign and outline lighting outlets shall be calculated at a minimum Load of 1200 volt-amperes for each required branch circuit specified in 600.5(A). 


Important!!!
Section 220.14(F) assigns 1200 volt-amperes as a minimum circuit load for the signs and outline lighting branch circuit, but  If the actual load for a sign and outline lighting unit is known to be larger than 1200 VA, then the actual load is used for calculation purposes.


Fig.2


Important!!!
Sign and outline lighting shall be considered to be continuous loads and must be multiplied by 1.25 for the purposes of feeder and protection calculations.
As per section 600.6, each sign and outline lighting unit must be controlled by an externally operable and dedicated disconnecting means (switch or circuit breaker) that opens all ungrounded Conductors simultaneously as shown in Fig(2) above.




D- Location and Rating of sign and outline unit Disconnecting Means


a- Location:
As per section 600.6(A), the following conditions shall be applied:


Fig.3

  • as in example#1 & 2 in Fig (3) above, The disconnecting means shall be within sight of the sign or outline lighting system that it controls. and as in example#3 in Fig (3) above, Where the disconnecting means is out of the line of sight from any section that is able to be energized, the disconnecting means shall be capable of being locked in the open position. 

  • For signs or outline lighting systems operated by mechanical or electromechanical controllers located external to the sign, the disconnecting means is required to be located within sight of (as in example# 2&3 in Fig (3) above)  or in the same enclosure as the controller and must be capable of being locked in the open position. 


b- Rating:
As per 600.6(B), The switch or flasher (not a circuit breaker) required to control the primary circuit of a transformer supplying a luminous gas tube, must have a current rating that is at least twice the current rating of this transformer. 


Important!!!
A disconnecting means shall not be required for cord-connected signs with an attachment plug.




Example#1:




A hardware store measures 80 feet × 120 feet. A portion of the building (80 feet × 40 feet) is used for storage. The remainder of the building is used as a showroom. There is a total of 45 feet of show windows, and there is one outdoor sign. What is the total lighting load for this building?



Solution:

Each type of lighting load is computed separately and then combined to determine the total lighting load.

First, the general lighting loads
We have two areas in the store:

Storage area = 80 feet × 40 feet = 3200 ft2

Showroom area = 80 feet × 80 feet = 6400 ft2


Table 220.3(A) included in the previous article 
Branch Circuit Design Calculations – Part Three " lists unit loads for storage and showroom as 1/4 VA/ft2 and 3 VA/ft2, respectively, then: 

General lighting load (storage) = 3200 ft2 × 1/4 VA/ft2 = 800 VA

General lighting load (showroom) = 6400 ft2 × 3 VA/ft2 = 19,200 VA

Total General lighting load = 800 VA + 19,200 VA = 20,000 VA



Second: The show-window lighting load
The show-window lighting load is based on 200 VA per linear foot:

Show-window lighting load = 45 feet × 200 VA/ft = 9000 VA



Third: sign lighting
The minimum load for the sign lighting is used: Sign lighting = 1200 VA

Now the total lighting load of the building can be calculated by adding the parts together: 
Total lighting load of the building = 20,000 VA + 9000 VA + 1200 VA = 30,200 VA 

These loads are all continuous, so the total load is multiplied by a factor of 1.25 to determine the circuit requirements. 


So, Total lighting load of the building = 30,200 VA × 1.25 = 37,750 VA




5- Additional lighting loads

5.1 Definition

The additional lighting loads are those loads not covered by NEC Code such as:

  1. Security lighting, 
  2. Parking area lighting, 
  3. Sidewalk lighting, 
  4. Roadway lighting, 
  5. Stadium lighting, 
  6. Tunnel Lighting. 



5.2 Rules applied for Calculation of additional 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 " Advanced Course for Lighting Design - Level I ".


Important!!!
All Additional lighting loads should be computed separately from the general lighting load and then added to the general lighting load.


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.



In the next article, I will explain Design Calculations for Receptacle Branch-circuits. So, please keep following.



3 comments:

  1. Hello Eng. Ali,

    There's another doubt here pertaining to Show window lighting - Why load for receptacles is omitted here? Kindly help.

    Thanks.

    Naveen

    ReplyDelete
    Replies
    1. Hi Naveen,

      as you see in example#1, the required is to calculate the total lighting load only of the building. so, I didn't calculate the receptacle load of the show window lighting because it is not a lighting load.

      and if the receptacles supply the show window lighting load, the load will be smaller than if it is not. and usually in design we take the worst case into consideration (larger load in this case).

      Delete

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