To add a subpanel, plan the load, pull a permit, run a 4-wire feeder, and isolate neutral and ground while keeping required working space.
Adding a subpanel gives you more circuit spaces without replacing the main service. This guide lays out the planning, safety checks, code touchpoints, and the hands-on sequence so you can decide what to do yourself and what to hand off to a licensed electrician. You’ll see where permits apply, how to size the feeder, and the steps to mount and wire a clean, inspection-ready subpanel.
Quick Planning Checklist And Code Touchpoints
Use this table to scope your job before you buy parts or open the main panel. It front-loads the safety and inspection items most homeowners miss.
| Item | What To Confirm | Typical Standard/Note |
|---|---|---|
| Permit & Inspection | Is a homeowner electrical permit required? | Most areas require a permit for new feeders/panels (check your city or state portal). |
| Panel Location | Clear front working space and access | ≥30″ width, ≥36″ depth, ≥78″ height in front of panel. |
| Feeder Conductors | 4-wire only (hot-hot-neutral-equipment ground) | Required for feeders to subpanels; neutrals and grounds kept separate. |
| Neutral/Ground Isolation | Neutral bar floating; bond screw removed | Bond only at service disconnect; subpanels isolate neutral from enclosure/EGC. |
| Feeder Sizing | Wire gauge and breaker sized for ampacity | Use NEC 310.16 ampacity (conductor rating & terminations). |
| Detached Structures | Grounding electrode system present | Separate building needs grounding electrodes per 250.32(A). |
| Protection | Where GFCI/AFCI is required on new branch circuits | Follow NEC 210.8 & 210.12 locations and device types. |
| Panel Fill | Spaces and manufacturer-approved tandems | Use the labeling inside the panel; don’t overfill or mix unlisted breakers. |
What A Subpanel Does And When It Makes Sense
A subpanel is a distribution panel downstream of the main service. It’s fed by a two-pole breaker in the service equipment and splits that power into new branch circuits. Add one when the main panel is out of spaces, when a workshop or addition needs local breakers, or when you want to segment loads for convenience.
You can add a small 60A panel for a few new circuits or go larger for growth. The physical size doesn’t set the current; the feeder breaker and wire gauge do. The method below shows how to plan both safely.
How to Add a Subpanel: Step-By-Step
1) Plan The Load And Size The Feeder
List the circuits you want now and what you might add later. Pick a subpanel rating (60A, 100A, or 125A are common). Then choose a feeder breaker and conductor that meet ampacity for the installation conditions. Ampacity comes from NEC Table 310.16 (by insulation and temperature rating); terminations usually limit residential feeders to the 60°C or 75°C column, depending on equipment ratings.
2) Confirm Working Space And Mounting
Pick a spot with clear floor area and headroom. Don’t place the panel in clothes closets or bathrooms. Keep the front clearance at least 36 inches deep, 30 inches wide (or the equipment width), and 78 inches tall so an inspector can work safely. These dimensions match code requirements adopted in residential codes.
Working space dimensions are spelled out in model codes that jurisdictions adopt, so this rule travels well.
3) Pull A Permit And Schedule Inspection
Adding a feeder and panel almost always needs a permit. Many states and cities let homeowners pull a permit for their own one- or two-family dwelling work. Your local portal will list who can do the work, fees, and how to schedule inspections. See this state page on electrical permit basics for a typical example.
4) Choose The Subpanel And Breakers
Pick a load center that matches the brand and breaker style you plan to use. Look for a main-lug only panel for subpanel use (or a main-breaker style if you want a local shutoff). Confirm an add-on ground bar kit is available for the exact model, since neutrals and equipment grounds will be on separate bars.
5) Run The 4-Wire Feeder
From the service equipment, run two ungrounded conductors (hot), one grounded conductor (neutral), and one equipment grounding conductor to the subpanel. Use conduit or cable as allowed by your local code and the building. In the same building, the feeder must be 4-wire with neutrals and equipment grounds isolated in the subpanel. For detached buildings, you also need a grounding electrode system at the structure.
6) Mount The Subpanel And Add Bars
Mount the subpanel plumb and at a reachable height. Install the ground bar kit if it’s not factory-installed. Leave the neutral bar isolated from the metal box (remove the green bonding screw or strap supplied for service-panel use). This keeps neutral current off the enclosure and off the equipment grounding conductors.
7) Terminate The Feeder
At the subpanel: land the two hots on the main lugs (or main breaker), the neutral on the insulated neutral bar, and the equipment ground on the ground bar. Torque to the labeling values. At the main panel: install the two-pole feeder breaker in spaces that land on opposite phases, connect the hots, then the neutral to the neutral bar, and the equipment ground to the grounding bar.
8) Label And Dress Conductors
Neatly dress the conductors, follow bend radiuses, and cap any unused openings with listed filler plates. Label the subpanel as a “Subpanel fed from Main #__ at ___A” and label the feeder breaker with the destination. Good labeling speeds the inspection and helps later work.
9) Add Branch Circuits And Protection
When you add new circuits, apply the current GFCI and AFCI rules for their locations. Kitchens, bathrooms, outdoor outlets, garages, and basements need GFCI. Most living spaces require AFCI. Combination devices or dual-function breakers make compliance cleaner in many panels.
Using The Keyword In Context: How to Add a Subpanel
If you’re searching how to add a subpanel for a workshop or an EV outlet, the main choices are feeder size, subpanel rating, and the route your cable or conduit will take. The steps above keep the project tidy and inspection-ready while leaving room for future circuits.
Feeder Sizing Basics Without Guesswork
Pick A Panel Rating And Back Into The Feeder
Common pairings look like this: a 60A subpanel fed by #6 copper THHN/THWN-2 in conduit on a 60A breaker; a 100A subpanel fed by #3 copper THHN/THWN-2 on a 100A breaker. Aluminum feeders are larger by gauge size for the same ampacity. Always confirm your termination temperature ratings and ambient conditions, since ampacity depends on both.
Mind Termination Ratings
Residential panels often have 75°C-rated lugs; older equipment may be 60°C. Use the correct ampacity column for your conductor insulation and the limiting termination rating so conductors aren’t undersized by mistake.
Example Feeder Pairings (For Planning)
These examples are common in residential work. They’re not a substitute for reading the panel label and checking conductor ampacity for your installation.
| Subpanel Rating | Typical Copper Feeder (THHN/THWN-2) | Matching Feeder Breaker |
|---|---|---|
| 60A | #6 Cu hots/neutral + #10 Cu EGC (in conduit) | 60A 2-pole |
| 70A–80A | #4 Cu hots/neutral + #8 Cu EGC | 70A–80A 2-pole |
| 100A | #3 Cu hots/neutral + #8 Cu EGC | 100A 2-pole |
| 125A | #1 Cu hots/neutral + #6 Cu EGC | 125A 2-pole |
| 60A (Aluminum) | #4/3 Al XHHW-2 + #8 Cu/Al EGC (check lugs) | 60A 2-pole |
| 100A (Aluminum) | #1/0-1 Al XHHW-2 + #6 Cu/Al EGC | 100A 2-pole |
| Detached 60A | Same as 60A above + grounding electrodes at structure | 60A 2-pole |
Wire sizes are drawn from commonly used ampacity values for 75°C terminations and 90°C insulation ratings, subject to adjustment and correction factors. Always verify with the current NEC table and your equipment labels.
Bonding And Grounding Rules You Can’t Skip
Neutral Isolated, Ground Bonded
In a subpanel, the neutral bus must be isolated from the metal cabinet and from the equipment grounding bus. The equipment grounding bus bonds to the metal cabinet. The neutral-to-ground bond exists only at the service disconnect, which keeps neutral current from flowing on metal raceways or ground wires downstream.
Detached Buildings Need Grounding Electrodes
If the subpanel feeds a separate building, install a grounding electrode system there and bond it to the subpanel’s equipment grounding bus. Two ground rods are common where the measured resistance can’t be verified. This requirement comes from NEC 250.32(A) as explained in trade guidance.
Keep The Working Space Clear
Store nothing in the 30″-by-36″ working footprint in front of the panel, and leave headroom to 78″. That clear zone protects anyone operating or servicing the equipment. See the model-code wording adopted into residential codes: general electrical requirements.
GFCI And AFCI At The New Circuits
When you extend or add circuits from a new subpanel, apply today’s protection rules for the room or location. Garages, outdoor outlets, basements, kitchens, and bathrooms need GFCI; most living areas need AFCI. Many manufacturers offer dual-function breakers that satisfy both in one device for standard 120V branch circuits. A consolidated summary of 2023 NEC changes is here.
Permit, Inspection, And Paper Trail
Most jurisdictions require a permit to install a subpanel because it adds a feeder and alters the distribution system. A permit brings inspections that catch hazards early and create a record helpful for insurance and resale. See a typical city process for residential electrical permits. Your local page will list homeowner eligibility, inspection scheduling, and contact info for questions.
Clean Installation Details That Inspectors Like
Conductor Preparation
Use anti-oxidant on aluminum per the lug labeling. Strip neatly without nicking strands. Follow the panel’s torque chart with a calibrated screwdriver or torque wrench.
Label Everything
Every new breaker and circuit gets a plain-language label. Add an engraved label on the subpanel door indicating the feeder breaker location and size.
Neat Routing
Keep conductors along the gutters, not across the face of the breakers. Bundle only where allowed and avoid crowding the neutral bar.
Troubleshooting Common Mistakes
Bond Screw Left In
If the neutral bond screw is still installed, the enclosure becomes a parallel return path for neutral current. Remove the screw, move equipment grounds to a dedicated ground bar, and confirm the neutral bar is floating.
Three-Wire Feeder
A three-wire feeder to a subpanel inside the same building isn’t allowed under modern code cycles because it bonds neutral and ground downstream. Upgrade to a 4-wire feeder so the neutral stays isolated.
Working Space Used As Storage
Boxes, shelves, or appliances in the clearance zone can cause a failed inspection. Clear the 30″-by-36″ area before the inspector arrives.
Tools, Materials, And Skill Line
Core Tools
Fish tape, drill with bits for studs or masonry, knockout set (for metal boxes), side cutters, strippers sized for your wire, torque screwdriver or small torque wrench, and a multimeter.
Materials
Load center (main-lug or main-breaker type), ground bar kit, matched breakers, listed cable or conduit with wire (two hots, neutral, equipment ground), fittings, anti-oxidant (for aluminum), labels, and panel screws.
DIY Or Hire?
Many homeowners can mount the panel, run conduit, and pull cable cleanly. Energizing, landing conductors in the service equipment, and final testing are where many bring in a licensed electrician. If you’re not comfortable working in a live service cabinet, hire that part out and still pass inspection with your own prep work.
How to Add a Subpanel For An Addition Or Shop
If your project is an addition or detached shop and you’re learning how to add a subpanel for that space, plan for a conduit sleeve between buildings, a 4-wire feeder, and grounding electrodes at the outbuilding. Keep trench depth and conduit type to local rules, and place the disconnect where conductors first enter the structure if required by your AHJ.
Final Walkthrough Before You Call For Inspection
- Panel location: clear, dry, and accessible; working space verified.
- Ground bar installed and bonded; neutral bar isolated; bond screw removed.
- Feeder is 4-wire; conductor sizes match breaker rating and termination limits.
- Detached structure (if any) has grounding electrodes bonded together.
- New circuits labeled; required GFCI/AFCI protection present for their locations.
- Deadfront installed; no open knockouts; all fittings listed and tight.
References Used While Writing
Core rules referenced include working-space dimensions adopted in residential codes and the NEC’s grounding, bonding, and protection requirements summarized by respected trade sources and state agencies. See the model-code working space requirement, state guidance on electrical permits, the NEC 310.16 ampacity references used by industry tables, and a consolidated view of 210.8/210.12 updates for GFCI/AFCI.