Two circuits' neutral conductors share a single terminal on the panel's neutral bar. The concern is:

One neutral per terminal is a rule with a specific and slightly non-obvious reason. Neutral conductors carry current — the full return current of their circuit — so a loose terminal shared by two of them is a heating point for both, and terminals designed for one conductor do not grip two reliably. The more important hazard appears during service. If an electrician lands on one circuit and loosens that terminal to remove its neutral, the other circuit's neutral is loosened at the same time. If that second circuit is still energised and under load, its return path is interrupted while its hot remains live, which puts the technician in the current path and can also drive voltage onto the disconnected neutral. That is why the requirement is one conductor per terminal even where the physical fit seems adequate, and why the finding is written as a service-safety hazard rather than a capacity issue.

Terminals are designed for a single conductor, so a shared terminal grips poorly and can loosen. The greater hazard is during service: removing one circuit's neutral disturbs the other's while it may still be energised and under load.

Panelboard neutral terminals are listed for one conductor each, and doubled neutrals are a common defect. Equipment grounding conductors may be doubled in some listings, which is why the rule is often misremembered as applying to both.

One Neutral, One Screw. Loosen it for circuit A and you have just opened circuit B's return — while B is still live.

Distinguish neutrals from grounds when you look. Inspectors frequently report doubled grounds as the same defect, which is often permitted by the panel's listing.

• •Reporting the concern as neutral bar overloading
• •Applying the one-conductor rule to grounds where the listing permits doubling
• •Missing that the hazard arises during future servicing