Wiring a detached garage seems straightforward until you pull the permit application and start reading the NEC. Detached structures have specific requirements that don't apply to wiring inside the main house — requirements around the feeder, the disconnect, and grounding that catch both homeowners and experienced electricians off guard. Here's what you need to know before you start.
Yes, You Need a Permit
Any new circuit from the main house to a detached structure requires an electrical permit in NJ. The permit subcode is F120, the same as any other electrical permit. There is no exception for small garages, workshops, or sheds — if you're running a circuit to a structure that isn't attached to the main dwelling, you're filing an F120.
The permit requirement exists for good reasons: detached structure wiring involves buried or aerial feeders, grounding systems, and disconnect requirements that are more complex than a typical branch circuit. These are exactly the conditions where uninspected work creates fire hazards years after the fact.
If you've already run wire to a detached garage without a permit, the path forward is to file now rather than leave unpermitted work in place. Inspectors are generally straightforward about retroactive permits for work that meets current code.
The NEC Rules for Detached Structures
The National Electrical Code — which NJ adopts — treats detached structures differently from circuits that stay within the main dwelling. The key sections are NEC Article 225 (outside branch circuits and feeders) and NEC Article 250 (grounding and bonding). Here's what they require:
4-wire feeder required. The feeder from the main house to a detached garage must be a 4-wire feed: two ungrounded conductors (hot), one grounded conductor (neutral), and one equipment grounding conductor (ground). This is the requirement that most often catches contractors who learned the old way. Prior to the 2008 NEC, a 3-wire feeder (two hots, one neutral — shared neutral and ground) was acceptable for detached structures. It is no longer. NJ has adopted code editions that require the 4-wire feed. Running 3 wires to a detached structure is a code violation and will fail inspection.
The reason for the 4-wire requirement is fault protection: a 3-wire feed creates conditions where a neutral fault can energize the metal parts of the subpanel and everything connected to it. The 4-wire feed provides a dedicated fault path separate from the neutral.
Separate disconnect required at the structure. The detached garage must have its own disconnect means — typically a subpanel with a main breaker, or a separate disconnect switch. You cannot rely on the breaker at the main house to serve as the disconnect for the detached structure. The disconnect must be accessible at or near the structure, so that power can be cut without going back to the main panel.
Ground rod required at the detached structure. This one surprises a lot of people: even though you're running a 4-wire feeder from the main panel (which includes a ground conductor), the detached structure still requires its own grounding electrode — typically a ground rod driven into the earth at the garage. The equipment grounding conductor from the main panel bonds to this local ground rod, establishing a reference to earth at the structure.
The neutral and ground must be treated as separate conductors at the detached structure's subpanel: isolated neutral bus, with the neutral not bonded to the panel enclosure or ground bus. The neutral-to-ground bond exists only at the main panel, not at the detached subpanel.
What Size Service to Run
The most common mistake homeowners make when planning a detached garage circuit is underestimating what they'll actually want to power. A 60A subpanel is the practical minimum for a functional garage — it supports lighting, receptacles, a single-car door opener, and one moderate load like a small compressor or bench grinder.
If your plans include any of the following, step up to 100A (or larger):
- EV charging. A Level 2 EV charger (240V, 40A or 50A) is already half of a 60A subpanel by itself, leaving little room for anything else.
- Heavy equipment. A table saw, welder, dust collector, or air compressor often require dedicated 240V circuits. Running two or three of these on a 60A panel gets tight quickly.
- Heated or cooled space. An electric mini-split, baseboard heat, or window AC unit can draw 15–20A continuously.
The cost difference between running a 60A feeder and a 100A feeder is modest — mostly the wire gauge (6 AWG vs. 3 AWG for aluminum) and the breaker size. The cost to upgrade later, including trenching, rewiring, and a new permit, is significantly higher. Size the feeder for what you'll want in five years, not just today.
GFCI Requirements
All 15A and 20A, 125V receptacles in a garage must be GFCI-protected under the NEC — this applies to detached garages as fully as to attached garages. There are no exceptions for workshop areas or "utility" receptacles. Every standard outlet in the garage needs GFCI protection, either via a GFCI outlet device or a GFCI circuit breaker.
This is enforced at final inspection. The inspector will test the GFCI function of every receptacle.
PSE&G ESI Implications
If your plan to wire the detached garage requires upgrading your main electrical panel — because the existing panel is full, undersized, or aging out — then the garage project may trigger a PSE&G Electric Service Installation (ESI) application. An ESI is required any time the existing meter and service entrance are modified.
Adding a subpanel circuit to an existing 200A main panel with available capacity does not typically require an ESI. But if you're upgrading from 100A to 200A service to support the garage plus other planned work, you'll need to file with PSE&G (or JCP&L in their territory) in parallel with the F120 permit. ESI processing typically takes 4–8 weeks for residential work.
Common Mistakes on Detached Garage Permits
Running a 3-wire feeder. The most common NEC violation on detached garage work. It will fail rough-in inspection. If wire is already in the trench, it's less expensive to pull it now than after backfill.
Skipping the disconnect at the structure. A plain subpanel without a main breaker doesn't satisfy the disconnect requirement unless it's a 6-circuit or fewer panel where the individual breakers collectively serve as the disconnect (the "six-circuit rule"). Anything larger needs a main breaker.
Not installing the ground rod. Easy to overlook. The inspector will look for it. Drive the rod before backfilling — doing it after the trench is closed means hand-digging or directional boring at the structure.
Bonding neutral and ground at the subpanel. Common habit from main panel work. At a subpanel (including the detached garage panel), the neutral and ground must be separated — isolated neutral bus, no bonding jumper. An inspector who opens the panel and sees the neutral bonded to the enclosure will reject it.
The Inspection Sequence
Detached garage electrical work typically requires two inspections:
Rough-in inspection: After the feeder is run and the subpanel is roughed in, but before the trench is backfilled and before interior wiring is covered. The inspector checks the feeder wire type and gauge, conduit installation (if used), panel rough-in, and ground rod installation.
Final inspection: After all receptacles, fixtures, and covers are installed. The inspector checks GFCI function, breaker labeling, and final panel work.
Don't backfill the trench before rough-in inspection passes. The inspector needs to see the burial depth and the wire type.
How ClearPath Handles the Permit
ClearPath files the F120 application for detached garage work including the load calculation documentation — which the municipality requires to verify that the main panel has capacity for the new feeder circuit. We're familiar with the 4-wire feeder and grounding requirements and will flag any scope issues before they become deficiency notices.
If you're a homeowner or contractor planning a detached garage circuit in NJ, contact us for a flat-fee permit quote.