How to Connect a Portable Generator to a Detached Garage Subpanel (2026)
Feeding a detached subpanel requires an isolated neutral busbar, four-wire feeder conductors, and a mechanical interlock kit. The generator must feature a floating neutral to prevent parallel ground paths.
01 Understanding Detached Subpanel Grounding
Detached garages and workshops are fed from main home electrical panels via four underground conductors: two hots, one insulated neutral, and one equipment ground.
Under National Electrical Code Article 250, neutral and ground busbars must remain strictly separated inside the subpanel with zero green bonding screws installed.
- Subpanels must maintain completely separated neutral and ground busbars.
- Generator connecting to subpanel must have a floating neutral.
- Requires mechanical interlock to isolate feeder from main house panel.
02 Subpanel Interlock Installation Steps
Install a 50-amp double-pole breaker in the subpanel and fit a UL-listed mechanical interlock plate over the main feeder disconnect.
Mount an exterior power inlet box, such as the Reliance PB50, on the garage exterior to receive generator power safely.
- 1 Verify Subpanel Isolation: Confirm neutral bonding screw is removed from the subpanel chassis.
- 2 Install Subpanel Interlock: Mount mechanical sliding plate over the subpanel feeder breaker.
- 3 Connect 50A Power Inlet: Wire 6-AWG copper conductors from outdoor inlet box into generator breaker.
- Keep neutral and ground isolated to prevent dangerous parallel ground loops.
- Verify the generator has a floating neutral configuration.
- Use heavy 6-AWG copper wire for all 50-amp feeder circuits.
Frequently Asked Questions
Q: Can power flow backwards from my garage subpanel to my main house panel?
Yes, if the subpanel feeder breaker is left ON. An interlock plate on the subpanel disconnect ensures garage power is isolated during generator operation.
Q: Does my detached garage require its own grounding rods?
Yes. NEC Article 250.32 requires detached structures fed by a subpanel to have a grounding electrode system consisting of two driven ground rods.