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).]