James “J.J.” Jones Jr., senior electrical engineer for BPLW Architects & Engineers Inc., El Paso, Texas, took these photos (at left) of an existing computer server room inside an office building. The feeder serving the room is single-phase. It originates from a panel about 50 ft away.
The contractor tapped phases B and C respectively by sharing the same lug as the incoming main feeder serving the panel. Photo 2 (below left) shows the incoming feeder entering a semi-recessed 100A, three-pole disconnect switch. The phase wires terminate on Phases A and C. Improper color-coding of the phase conductors is evident. The neutral wiring coming from the panel does not terminate on a solid neutral bar; it lands on the load side, Phase B. A particular favorite is the “braiding” of the ground wire in order to terminate on the field installable ground kit. The feeder supplying the panel shows the color-coded phase wires that originate from the disconnect switch on Phases A and C, but end up landing on Phases B and C. I think the electrician noticed this “screw-up,” but did not have enough “slack” to properly terminate the phase wire on the “A” lug, and considered the next best thing and jumped it. The outlets in the server are fed out of this panel, and they are all isolated grounding type.