question; an office building has a total area of 50,000 sf, the actual number of gen-purpose receptacle outlets is unknown and the connected load equals the calculated load. how many 120 volt,2-wire,20 amp branch circuits are for the lighting and receptacles ? I missed this one on a practice exam. the options were,21,92,112,or 118. can someone could show me the calculations,.... thanks
Look at Table 220-3(a), if you look at the table for office buildings it gives you a value of 3.5 v/a per sq. foot BUT there is a footnote 'b'...if you read this footnote it indicates you must ADD an additional 1 v/a per sq. ft. for general-purpose receptacle outlets where the actual number of receptacle outlets is UNKNOWN.
Therefore you have a total v/a per sq. ft. of 4.5 calculated as follows:
3.5 v/a x 50,000 sf. = 175,000 va x 125% (lighting is considered a continuous load) = 218,750 v/a + 50,000 v/a (1 v/a per sf for unknown receps) = 268,750 va/120v = 2239.58A /20A ckt rating = 112 circuits
Go to RKeiss' website (www.elec-toobox.com), in his 'Code Quiz' section, May, 2001, quiz question #6 - he takes you through the steps of computing the answer for the same situation you asked.
[This message has been edited by dana1028 (edited 06-19-2003).]
because they are applying the 1 va to the recep load and applying the 3-1/2 va to the lighting load...lighting loads are considered continuous loads in non-dwelling occupancies....if you read the title to the table " General Lighting Loads"
...per your calculations - 117.19 is rounded down, not up (see 220-2b)...117 is not one of the options for an answer.
[This message has been edited by dana1028 (edited 06-20-2003).]