No neutral-to-ground connection past the main
After the service disconnect, the neutral may not be connected to metal enclosures, boxes or equipment frames. Subpanels keep neutrals and grounds separate, with only a few narrow exceptions.
What the code requires
On the load side of the service disconnect, or of a separately derived system's disconnect or overcurrent devices, the neutral may not be connected to metal parts that do not normally carry current. The code permits such connections only where 250.30(A)(1), the existing-installation exception in 250.32(B)(1), or Part X of Article 250 allows them.
In practice, a subpanel fed from the main panel keeps its neutrals isolated from the enclosure and its equipment grounds on a separate path.
On the job
- A subpanel with the bonding screw or strap still installed is a common correction.
- Neutrals and grounds landed on the same bar downstream of the main disconnect get flagged.
- New range or dryer circuits that use the neutral as the equipment ground, the old 3-wire hookup, are a fail. That arrangement is allowed only for existing installations.
Exceptions that matter
- Existing range, oven, cooktop and dryer installations may keep using the neutral to ground the appliance frame under 250.140.
- Meter enclosures on the load side may connect to the neutral if there is no ground-fault protection of equipment, all meters are immediately next to the service disconnect, and the neutral is at least the Table 250.122 size.
Related sections
- NEC 250.24: Grounding and bonding at the service
- NEC 250.30
- NEC 250.32: Grounding at detached garages, ADUs and outbuildings
- NEC 250.140
- NEC 408.40
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CSLB #354550 · C-10 Electrical · Licensed since 1978 · $25,000 contractor's bond