Funny you should ask today of all days. I just installed a new 800A 1Ø service in a new church. Today the utility came to hook us up. They set a 100kva pad mount transformer yesterday and ran 2 runs of 500MCM aluminum URD tri to my 800A MDP. They had marked both ends of each set of conductors as follows: L1-Red, L2-Blue, neutral-unmarked(has a yellow stripe). The URD sets entered the panel via (2)3" PVC LBs nippled to the *00A panelboard. I took a Red(L-1) from each set and connected to the L-1 buss lugs and a Blue(L-2) from each set and connected to the L-2 buss lugs and connected both of the neutrals to the neutral buss which was bonded to the enclosure and grounded via (4) 5/8"x8' ground rods cadwelded with #4 bare CU. The utility thoroughly inspected my connections to make sure they suited them before I closed up my panelboard. Well, today they came back to connect the transformer to the primary. They closed the cut-out on the pole and told me to check voltage. I had nothing. They opened and closed the cut-out a couple more times and I still had nothing. They opened the cut-out and opened the transformer and discovered that they had on each stud block(L-1 and L-2)one red and one blue marked conductor! Luckily the transformer had a fused secondary. The secondary fuse was vaporized! This was a Kohlman 2400V primary, 240V secondary 100Kva pad mount shorted phase to phase. Thank God it had a fused secondary. I saw a 67Kva pad mount without secondary fusing become shorted when a trencher cut the secondary a few years ago and it blew the bushings out. Kind of as if someone tossed a grenade in it.
Side note: The two guys who energized the transformer today were not the same two who installed the secondary and terminated the transformer yesterday but all four were veteran utility workers with 20+ years of experience. EVERYBODY makes mistakes!
