John, It's a grounded Delta setup. You have 3 transformers on the pole that are hooked in a Delta. One corner of the Delta is grounded. In the fuse box, that grounded phase will have a shorting bar instead of a fuse. Since there is no center tap on any transformer, you have 480 on phase A to B, 480 on phase B to ground, and 480 on phase A to ground.

If you google ISBN 0-538-33550-5 you'll get some hits for a decent book on this stuff that is written for someone that's not an Electrical Engineer, and covers all the different situations. Here's one link for a used book that seems reasonably priced: http://search.barnesandnoble.com/used/productMatches.asp?r=1&PEAN=0538335505