Detached Garage Feeder With Neutral Bonded at Subpanel
A detached garage is 85 ft from the house. The homeowner wants a 60 A, 120/240 V subpanel for lights, receptacles, a 240 V compressor, and a future EV outlet. The electrician installs 6 AWG copper THWN in 1-1/4 in PVC, buried 18 in. The feeder contains two ungrounded conductors, an insulated neutral, and a bare copper equipment grounding conductor. At the garage, the neutral bar is bonded to the panel enclosure and to a new ground rod; the equipment grounding conductor is also landed on the neutral bar. The PVC crosses under a gravel driveway for 12 ft. The inspector red-tags the job. The electrician argues that the ground rod at the garage makes the equipment grounding conductor unnecessary and that 18 in is always enough for PVC.
1. Is the grounding and bonding arrangement at the garage subpanel acceptable? Explain the roles of the neutral, equipment grounding conductor, and ground rod.
Read the worked answer
No. The garage is a separate structure fed by a feeder, and a 120/240 V feeder to it must include an equipment grounding conductor. At the subpanel, the neutral must be isolated from the enclosure and from the equipment grounding conductor. The ground rod is a grounding electrode, not a substitute for the equipment grounding conductor.
The correct arrangement is:
- Run a separate equipment grounding conductor with the feeder.
- Land the equipment grounding conductor on the equipment grounding bar in the garage panel.
- Keep the neutral on an isolated neutral bar; remove the bonding screw or strap.
- Connect the ground rod to the equipment grounding conductor/grounding electrode system, not to the neutral.
- Bond the panel enclosure to the equipment grounding conductor.
Bonding neutral to ground at the garage creates a parallel return path for neutral current through the equipment grounding conductor and grounding electrode, which can energize metal parts and cause objectionable current. The electrician’s argument that the ground rod makes the equipment grounding conductor unnecessary is incorrect.
2. What burial depth is required for this feeder, and does the PVC raceway change the answer? What corrections are needed before re-inspection?
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PVC raceway does not eliminate the burial-depth rules. The general minimum cover for PVC conduit is 18 in, but the feeder crosses under a driveway. Conductors under driveways, parking lots, roads, and similar areas require 24 in of cover unless a more specific permitted method applies. Because this PVC crosses under a gravel driveway for 12 ft, the 18 in installation is too shallow for that portion.
Before re-inspection:
- Lower the driveway crossing to the required 24 in cover, or redesign the crossing using a method the AHJ accepts.
- Verify the remainder of the run meets the applicable cover requirement for PVC.
- Separate the neutral and equipment grounding conductors at the garage panel and remove the neutral-to-ground bond.
- Connect the ground rod to the equipment grounding conductor system.
- Confirm conductor ampacity and overcurrent protection for the 60 A feeder, and verify any GFCI requirements for garage receptacles.
- Provide inspection access and documentation for the buried portion before backfilling.
3. What tests and observations should the electrician complete before asking for re-inspection?
Read the worked answer
Before re-inspection, the electrician should verify both the physical installation and the electrical continuity of the grounding system:
- Confirm the neutral bar is isolated and the enclosure is bonded only to the equipment grounding conductor.
- Confirm the ground rod connection is made to the equipment grounding conductor with an approved clamp and conductor.
- Check equipment grounding conductor continuity from the house grounding system to the garage panel and to all garage receptacle grounding terminals.
- Verify branch-circuit overcurrent protection and GFCI protection where required.
- Check torque on feeder terminations and confirm conductor identification.
- Photograph the trench and driveway crossing at the required depth before backfill.
A ground resistance test may be requested by the AHJ, but a pass/fail value is not a substitute for the required grounding electrode and equipment grounding conductor installation. The key point is that the ground rod does not replace the equipment grounding conductor.