One of your buildings is called "the cable morgue" because there's a cable failure every few months. You don't normally work in that building, but your boss is impressed with your troubleshooting acumen and wants you to identify potential causes and make recommendations.

You’ve already looked at the one-lines and a few other drawings. There's nothing especially troubling about the building. It's got a 4-wire 480V system and 6,000A service. In fact, it's much like the building where you work, and you don't have cable failures. Even the loads are similar, and harmonic content is moderate. What are some things you should be looking at?

Having your building to compare to allowed you to rule out, with reasonable certainty, the inherent demands of the load or the inadequacy of the wiring. You're really investigating a 2-part question. The first part is, "Why are these failures occurring?" The second part is, "Why can't they see these coming?"

If cables frequently fail, it's likely that un-failed cables are being damaged during the replacement of failed cables. Damage of adjacent cables is always possible, no matter how careful you are. Insulation resistance tests should be conducted before and after disturbing the cables. Also, visually inspect for moisture trails, rodent droppings, and abrasion.

A cable failure is usually a sign of a maintenance failure. Cable insulation degrades over time, and insulation resistance trending nearly always prevents outright failure.