Why must neutrals be isolated from grounds at subpanels?

• A. To prevent parallel current paths on the grounding system that can create shock hazards and nuisance trips
• B. To improve voltage regulation
• C. To allow the neutral conductor to carry current on the grounding path
• D. To simplify labeling requirements for subpanels

Answer: (A)

Separating neutrals and grounds at a subpanel keeps the grounding path free from normal current. The neutral carries current back to the power source during regular operation, while the equipment grounding conductor is a safety path reserved for fault currents to trip protective devices and keep metal parts at earth potential. If the neutral and grounding conductors were tied together at the subpanel, neutral current would have a parallel route on the grounding system and through metal enclosures. That means current could flow on parts that are supposed to be safe to touch, creating shock hazards, and it can cause nuisance trips or improper operation of protective devices because current would be taking unintended paths. By bonding neutrals and grounds only at the main service disconnect and keeping them isolated in subpanels, you ensure the grounding system remains a true safety path without carrying normal neutral current.