Basic calculations

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RCoiley

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I need help with a basic calculation please! I am missing something and cannot figure out what it is.. please help 🙏

A store building measures 60 ft. by 80 ft. and is supplied by a 240/120V, 3Ø, 4-wire delta system. Which of the following is the minimum allowable number of 2-wire, 20-ampere branch circuits required to supply the general lighting in this building?
(A) 6 (B) 7 (C) 8 (D) 9
 
I suggest you review example D3 (I'm in the 2017 NEC, my newest edition) in the informative annex in the back of the book.

Follow the references.

If you give your thinking and answer, people will respond quicker than you just asking the answer.
 
the supplied system is not relevant:

60*80=4800 square feet
@3va per foot *4800=14,400 total watts
20a * 120v = 2400 watts per circuit
2400*.8 = 1920 watts of continuous load (the real math is 1920 *1.25 = 2400)
14,400/1920 =7.5 so C is the answer.

That is all the steps, now, since you are obviously studying, Since I gave you the answer and the steps. I challenge you to cite the ohms law for step 3 and the code reference for steps 2 and 4
 
oldsparky52 said:
I suggest you review example D3 (I'm in the 2017 NEC, my newest edition) in the informative annex in the back of the book.

Follow the references.

If you give your thinking and answer, people will respond quicker than you just asking the answer.
Click to expand...
oldsparky52 said:
I suggest you review example D3 (I'm in the 2017 NEC, my newest edition) in the informative annex in the back of the book.

Follow the references.

If you give your thinking and answer, people will respond quicker than you just asking the answer.
Click to expand...
Trust me I have reviewed all the examples in the back of the code book.
 
Move the heading over so that va/m^2 and Va/ft^2 are over the col.
Table 220.12 General Lighting Loads by Non-Dwelling Occupancy
�
Type of OccupancyUnit Load
Volt-amperes/
m2		Volt-amperes/
ft2
Automotive facility161.5
Convention center151.4
Courthouse151.4
Dormitory161.5
Exercise center151.4
Fire station141.3
Gymnasiuma181.7
Health care clinic171.6
Hospital171.6
Hotels and motels, including apartment houses without provisions for cooking by tenantsb181.7
Library161.5
Manufacturing facilityc242.2
Motion picture theater171.6
Museum171.6
Officed141.3
Parking garagee30.3
Penitentiary131.2
Performing arts theater161.5
Police station141.3
Post office171.6
Religious facility242.2
Restaurantf161.5
Retailg,h201.9
School/university333
Sports arena333
Town hall151.4
Transportation131.2
Warehouse131.2
Workshop181.7
Note: The 125 percent multiplier for a continuous load as specified in 210.20(A) is included when using the unit loads in this table for calculating the minimum lighting load for a specified occupancy.
aArmories and auditoriums are considered gymnasium-type occupancies.
bLodge rooms are similar to hotels and motels.
cIndustrial commercial loft buildings are considered manufacturing-type occupancies.
dBanks are office-type occupancies.
e Garages — commercial (storage) are considered parking garage occupancies.
fClubs are considered restaurant occupancies.
gBarber shops and beauty parlors are considered retail occupancies.
hStores are considered retail occupancies.
220.14 Other Loads — All Occupancies
 
I haven't had any interaction with the 2020 code yet. Are they finally adjusting the the lighting levels per the chart Dennis attached in 2020?
 
oldsparky52 said:
I'll bet the question the OP posted is from a 2017 or earlier code edition and the correct answer is not an option.
Click to expand...
Based on the 2017 code 8 would be correct. But not on the 2020, that is what was confusing me to no end. I could not get it to work out no matter how many times I worked the equation.
 
Are you sure the test you are taking is for the 2020? The website still has it at 2017 and that particular question, as you know, is in the handbook online and is from the 2017 questions.

NC will not go to the 2020 Nec until Oct 1, 2021. They just passed the amendments along with the 2020 NEC this week or last week.
 
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