2008 License Test Prep Book, Commercial Calculations Chapter

skadee

Member
Location
Indianapolis
When does the 125% come into play for constant loads, and when does it not?

The answer key's answer for Question 6 in the Commercial Calculations Chapter does not factor in 125% for the lighting, but it does for questions 7 8 and 9. The question is in regard to warehouse lighting, which I would understand to be constant.

Is the answer in the answer key wrong for question 6? It says the answer should be (b).

Thanks
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
Not many of us have that book so you'll need to post the complete question and answers.

Welcome to the Forum. :)
 

skadee

Member
Location
Indianapolis
What is the general lighting and general-use receptacle feeder/service calculated load for a 250,000 sq ft storage warehouse that has 200 receptacles? (25, 56, 95 or 105 kVA?) The answer key indicates that the answer is 56 kVA, and the work-up suggests that the lighting is calculated at 100% (not 125%) Why wouldn't warehouse lighting be a constant load??
 

George Stolz

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Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Around here energy codes might dictate the use of occupancy sensors. A store would be lit for greater than three hours, but I've heard of warehouses where the lights come on as you walk.
 

skadee

Member
Location
Indianapolis
Around here energy codes might dictate the use of occupancy sensors. A store would be lit for greater than three hours, but I've heard of warehouses where the lights come on as you walk.
Construction standards in this area would dictate the same, but we've been advised that unless specifics are detailed (regarding continuous loads, aluminum wire, 60C vs 75C, etc.), when it comes to taking tests, don't assume real-world conditions, but use the details provided in the question. Since the question did not specify occ sensors (and we're using 2008 NEC to boot), I have to assume that there are no occ sensors.

Thanks
 

charlie b

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Seattle, WA
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Electrical Engineer
If you calculate lighting load on the basis of watts per square foot, any influence of the lights being a continuous load will have been taken into account by the number given in Table 220.12. So I would not use the 125% factor. This is different from calculating lighting load by saying, for example, that I have 100 light fixtures, each capable of holding two 32 watt bulbs, and therefore the lighting load is 6400 watts. I would use the 125% factor in that case.
 

skadee

Member
Location
Indianapolis
Ok. So if the table already factors in the 125%, then I have a contradiction in two of the subsequent book questions, here's one of those: "What is the feeder/general lighting calculated load for a 3200 sqft dance club? (3200, 6400, 8000 or 12000VA?)"

Now, I would have assumed this would be continuous load on the gen lighting as well, and Mike's calculation reflects the same. His calculation:
(3200 sqft x 2VA x 1.25) (ref 215.2(A), 215.3, 230.42(A), table 220.12)

If the club's lights are a continuous load, why not for the warehouse? The only difference in the question, that I see, is that he's asking for the feeder load, in this case.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
The contradiction comes all the way from the NFPA. Check out example D3 in Annex D. They don't see the contradiction right in front of their noses.

Table 220.42 should read "All Others = 125%" and get more specific about what qualifies for truly "100%". The table is completely ignored despite being referenced. Therefore, there is no right answer and we just have to guess at the intent. The service/feeder issue mentioned is not relevant, they follow the same rules.
 
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