Load Calculations for Show Windows

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wdingman

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Chicago
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Electrician
I am reviewing various exam preparation materials for my apprentices. I have discovered a difference of opinion when it comes to determining the calculated load for show windows:
  • Mike Holt's Illustrated Guide to Electrical Exam Preparation (2017 edition) does not add an additional 25% to the show window calculation based on the 200 VA per linear foot of show window (see page 496). The book does not say anything about the load being continuous or non-continuous. The illustration, however, is of a store so it would seem safe to assume that the load is continous.
  • In Ray Holder's Calculations: 2020 National Electrical Code, the author adds an additional 25% to the show window calculation. (See Exam 2, question 9). He adds this because the load is continuous.
Which of these approaches is correct?
 
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xformer

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Dallas, Tx
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Master Electrician
wdingman said:
I am reviewing various exam preparation materials for my apprentices. I have discovered a difference of opinion when it comes to determining the calculated load for show windows:
  • Mike Holt's Illustrated Guide to Electrical Exam Preparation (2017 edition) does not add an additional 25% to the show window calculation based on the 200 VA per linear foot of show window (see page 496). The book does not say anything about the load being continuous or non-continuous. The illustration, however, is of a store so it would seem safe to assume that the load is continous.
  • In Ray Holder's Calculations: 2020 National Electrical Code, the author adds an additional 25% to the show window calculation. (See Exam 2, question 9). He adds this because the load is continuous.
Which of these approaches is correct?
Click to expand...
IMHO, The load should be calculated as continuous. Since most commercial lighting is continuous. I personally have not seen many residential units with a sizeable show window. :)
 
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wdingman said:
I am reviewing various exam preparation materials for my apprentices. I have discovered a difference of opinion when it comes to determining the calculated load for show windows:
  • Mike Holt's Illustrated Guide to Electrical Exam Preparation (2017 edition) does not add an additional 25% to the show window calculation based on the 200 VA per linear foot of show window (see page 496). The book does not say anything about the load being continuous or non-continuous. The illustration, however, is of a store so it would seem safe to assume that the load is continous.
  • In Ray Holder's Calculations: 2020 National Electrical Code, the author adds an additional 25% to the show window calculation. (See Exam 2, question 9). He adds this because the load is continuous.
Which of these approaches is correct?
Click to expand...
That example follows the style of Annex Example D3 and is for the "Demand Load" value required by 220.14(G)(2) not the branch circuit or service load @125%. The Example in 11.9 shows the additional 125% added for a continuous load. If you have any other questions or suggestions feel free to email me Brian@MikeHolt.com - Brian House
 
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