A finger-tight neutral bus nearly burned a new apartment building. Why torque specs matter

The electrician described the find on Reddit's r/electricians on Nov. 7. With the neutral bus loose, return current headed back toward the service on the equipment grounding conductors and passed through a receptacle where a ground wire touched the neutral, overheating the 14 AWG conductors there. The crew noticed when sparks flew as a unit panel was connected and a receptacle would not work.

A loose termination is a high-resistance joint that heats under load, and the current of an open neutral looks for any other path. The grounding path is not built to carry it. Eastside Electrical, a Washington contractor, says in a guide based on the 2023 NEC that neutral current on grounding conductors and connected metal can overheat wiring and leave metal parts energized, and that an ordinary 15- or 20-amp breaker might stay closed. Under NEC 250.142(B), the guide explains, the neutral may not be used to ground equipment downstream of the service.

NEC 110.14(D), added in 2017, says that where the equipment or its paperwork lists a torque value in numbers, the installer must reach it with a calibrated tool. In 2020 the code swapped the tool requirement for "an approved means," a term that takes in shear bolts and breakaway indicators, and later editions kept the rule, according to Voltage Lab's review of the code. The site also warns against rechecking every lug on a panel that is already done, since every additional pass loads the screw beyond what it was built to take. Its advice is to torque each terminal once, mark it and record the value.