A sub-panel (also called a subpanel or auxiliary panel) is a secondary electrical distribution board that pulls power from your main panel and feeds circuits to specific areas of your home or property. Installing one always involves significant electrical work and almost always requires a permit. The trigger is simple: any new sub-panel installation typically requires a permit in every state that has adopted the National Electrical Code (NEC). The exceptions are rare and narrow — mainly like-for-like replacement of an existing sub-panel with the exact same amperage and configuration in the same location, and even then, many jurisdictions still require a permit. What varies widely is the process: some building departments handle electrical permits in-house, others require you to file through a licensed electrician, and some jurisdictions split the work between the building department and a separate electrical inspector. Most sub-panel permits fall into the $50–$500 range depending on amperage and project valuation. Plan for 1–4 weeks from filing to approval, plus inspection time after installation. The safest move is to call your local building department before you start — a 90-second conversation will tell you whether your specific scope needs a permit and which forms to file.
When a sub-panel installation needs a permit
A sub-panel installation is electrical work that modifies or extends your home's power distribution. The National Electrical Code (NEC) — adopted in some form by all 50 states — governs how sub-panels are designed, installed, grounded, and bonded. Because the stakes are safety (fire, electrocution, equipment damage), building departments treat sub-panel work as a permit-required activity in nearly all jurisdictions. The only genuine exemptions are extremely narrow: replacing an existing sub-panel with an identical new one (same amperage, same location, same feed) might be exempt in some jurisdictions, but many still require a permit even for that. A sub-panel powering a new detached structure (garage, shed, barn) almost always requires a permit. A sub-panel serving a new room addition, basement renovation, or outdoor living space (deck, hot tub, workshop) always requires a permit. Even a sub-panel installed solely to dedicated a certain amperage to one area (e.g., a 60-amp sub-panel for an electric vehicle charging station) requires a permit.
The permit trigger is really about whether the work involves new or modified electrical infrastructure. Three things determine whether you need a permit: (1) Is it a new sub-panel or a replacement of an existing one? (2) Is it in the same building or a detached structure? (3) What amperage is it, and what will it serve? New installations always require permits. Replacements in the exact same location with the same amperage are sometimes exempt, but this varies by jurisdiction — call first. Detached structures always require permits. Amperage doesn't usually determine exemption or cost by itself, but it does affect code requirements. A 100-amp sub-panel has different grounding and bonding rules than a 200-amp sub-panel. Your building department will ask for this information on the application.
Code-wise, the primary citations are NEC Article 225 (Outside Branch Circuits and Feeders), NEC Article 230 (Services), and NEC Article 408 (Switchboards and Panelboards). For sub-panels in detached structures, NEC 225.30 through 225.40 spell out the grounding and bonding rules — the main difference from a main panel in a home is that a detached structure sub-panel must have its own grounding electrode system (typically a ground rod) separate from the main house ground. This is the single most common mistake homeowners and unlicensed electricians make: they forget to install a ground rod at the detached structure or they bond the ground and neutral at the sub-panel (allowed at the main panel, forbidden at a sub-panel in a detached building). When your permit application goes to the building inspector or electrical inspector, they will flag this immediately if it's missing from the scope drawings.
Most jurisdictions require that sub-panel work be done by a licensed electrician, not by the homeowner. Some states allow homeowner-permitted work for certain projects (e.g., a homeowner can pull a permit and do their own electrical work in Minnesota, provided it's inspected), but sub-panels are often carved out as contractor-only work even in homeowner-permit states. Check your state's rules on this — it varies. If you're planning to hire an electrician, they will usually pull the permit themselves as part of their scope. If you're planning to do the work yourself, confirm with your building department whether you're allowed to be the permit applicant. Some jurisdictions will only accept a licensed electrician or licensed master electrician as the applicant for electrical permits. Others allow a homeowner to file if the work is owner-occupied residential property.
Timeline-wise, sub-panel permits are usually faster than major renovations but slower than cosmetic work. Most building departments process electrical permit applications in 1–4 weeks depending on completeness and backlog. Once approved, you have a window (typically 180 days to a year) to start and finish the work. The inspection itself is usually a single visit after the sub-panel is installed and roughed in but before drywall or permanent cover is installed. The inspector will check the feed from the main panel to the sub-panel, the breaker in the main panel, the grounding and bonding at the sub-panel (especially critical for detached structures), the wire gauge and conduit sizing, and the circuits branching off the sub-panel. Bring the stamped permit and be ready to answer questions about the scope.
Cost varies by jurisdiction and project scope, but most sub-panel permits run $75–$300 for the base permit. Some jurisdictions charge a percentage of project valuation (1.5–2% is typical) if you've estimated a high project cost. A 100-amp sub-panel in a finished basement might be valued at $3,000–$5,000 (including labor), pushing the permit fee to $50–$100. A 200-amp sub-panel in a new detached garage might be valued at $8,000–$12,000, pushing the permit to $150–$200. A few jurisdictions have separate fees for plan review, inspection, and reinspection if work fails the first time. When you call the building department, ask for the full fee schedule — don't guess. And confirm whether the fee is a flat rate or a percentage of valuation, because that affects how you estimate the project cost on the application.
How sub-panel permit rules vary by state and region
All 50 states have adopted the National Electrical Code as the baseline for electrical safety, but each state and many cities layer local amendments on top of it. The NEC is updated every three years; most states adopt a version that's 1–3 cycles behind the current one. As of 2024, most states are working with the 2020 NEC or the 2023 NEC. A few states (Florida, California, New York) have their own state electrical code that mirrors the NEC with state-specific amendments. For sub-panel work, this matters when it comes to grounding electrode requirements, bonding rules, and wire sizing in specific climates. For example, Florida Building Code (2023) adds specific requirements for sub-panels in coastal areas due to salt-air corrosion of aluminum conduit — you may be required to use stainless steel or PVC-coated conduit instead of standard aluminum EMT. California's Title 24 energy code adds requirements for sub-panels serving EV charging or heat-pump systems that don't appear in the base NEC.
Homeowner-permit eligibility varies sharply. In Minnesota, Texas, and several other states, a homeowner can pull an electrical permit for owner-occupied residential work and do the labor themselves, including sub-panels. In New York, California, and most northeastern states, electrical work must be done by a licensed electrician — the homeowner cannot be the permit applicant or the worker. In Florida, a homeowner can pull a permit for certain work but not for sub-panels or service upgrades; those require a licensed contractor. Your state's contractor licensing board or your building department's website will spell this out. If you're hiring a contractor anyway, this distinction doesn't matter — they'll pull the permit. If you're planning to do the work yourself, confirm your eligibility before you design the project.
Detached structures have the sharpest variation. All states require sub-panels in detached buildings to have their own ground rod (per NEC 225.32 for structures supplied by a feeder or branch circuit). But some states add extra layers: New York requires a minimum 8-foot ground rod in bedrock areas and mandates specific electrode materials in corrosive soils. Minnesota requires bonding of all metal structures and metal-water piping in a detached garage if a sub-panel is present. California requires seismic bracing of the sub-panel itself if it's in a high-seismic zone. These are all add-ons that won't show up in the base NEC but will show up when the inspector arrives. When you file a sub-panel permit for a detached structure, ask the building department explicitly whether there are state or local amendments that affect your scope — don't assume the base NEC is all you need.
Permit-filing process also varies. In many mid-sized cities (Madison, Denver, Portland), electrical permits are filed through the main building department and reviewed by in-house electrical inspectors or contracted electrical inspectors. In some large cities (New York, Los Angeles, Chicago), there is a separate Department of Electrical Safety or Bureau of Electrical Inspection with its own permitting portal and fee schedule. In rural counties, electrical permits may be filed through the county building department and inspected by a third-party electrical inspector under contract. Some jurisdictions now offer online filing for electrical permits (portal-based systems); others still require in-person or paper filing. A few states (Florida, California) have online portals at the state level for certain permit types. When you call your building department, ask whether they have an online system and, if so, whether sub-panel permits can be filed that way — it can save you a trip.
Common scenarios
Installing a 100-amp sub-panel in your basement to power a new workshop circuit
You need a permit. A sub-panel is a structural change to your electrical system, and anything that involves running a new feeder from the main panel, installing new breakers in the main panel, and adding a secondary distribution point requires a permit in every jurisdiction. The fact that it's in your own home (not a detached structure) doesn't exempt it. The fact that it's 'only' 100 amps doesn't exempt it. File an electrical permit with your building department or through your jurisdiction's online portal. Include a one-line diagram showing the main panel, the feeder run to the sub-panel, the main breaker in the sub-panel, and the circuit loads you plan to serve. If you're hiring a licensed electrician, they will pull the permit; if you're doing it yourself, confirm that you're eligible to pull an electrical permit in your state. Plan for 2–4 weeks from filing to approval, plus one inspection after installation. Cost: $75–$200 depending on your jurisdiction.
Adding a 60-amp sub-panel in your detached garage to power an electric vehicle charger and workshop equipment
You need a permit — and you'll need to be more careful about the details because it's a detached structure. Sub-panels in detached buildings trigger extra code rules, specifically NEC 225.30–225.40 on grounding and bonding. The critical rule: a sub-panel in a detached garage or outbuilding must have its own ground rod, bonded to the sub-panel, separate from the main house ground. This is different from a sub-panel in the same building as the main panel. When you file, include a site plan showing the distance from the house to the garage, the routing of the feeder (conduit, wire gauge, bury depth if underground), and a diagram showing the ground rod at the garage. The inspector will specifically check for the ground rod on-site — they will fail the inspection if it's missing. You will also need to confirm whether a 60-amp feeder from the main panel is adequate for both the EV charger and workshop load, or whether you need to upsize. Most building departments require that you size the feeder for the sum of the connected loads, not just the breaker rating. Work with a licensed electrician to size this correctly, or the permit will be bounced back for rework. Cost: $100–$250. Timeline: 2–4 weeks approval, plus 1 inspection.
Replacing an existing 200-amp sub-panel in your finished basement with a new 200-amp panel of the same make and model in the same location
This depends on your jurisdiction. Some building departments treat a like-for-like replacement of an existing sub-panel as exempt work, especially if it's in the same location and you're not changing the feeder, breaker, or load configuration. Others require a permit even for replacements because the work involves removing the old panel (potential safety hazard) and installing the new one (potential for improper bonding, grounding, or circuit labeling). Your safest move is to call your building department and describe the project: 'I have an existing 200-amp sub-panel in my basement. I want to replace it with a new 200-amp panel of the same size, same amperage, same location, with no changes to the incoming feeder or the breaker in the main panel. Do I need a permit?' If they say yes, file an electrical permit. If they say no, get that exemption in writing. Even if you don't need a permit, you likely still need a licensed electrician to do the work — most states don't allow homeowners to remove and reinstall sub-panels without a license. Cost: $0–$150 if a permit is required. Timeline: 1–2 weeks if a permit is needed.
Running a new 150-amp feeder to an existing detached garage that never had electrical service before, and installing a new sub-panel and circuits
You need a permit, and it's a more complex one. You're not just installing a sub-panel; you're extending electrical service to a previously unserved structure, which triggers multiple code sections and inspections. NEC Article 225 applies to the feeder run from the main panel to the garage (minimum #2 copper or #1/0 aluminum for a 150-amp run, bury depth depending on whether it's in rigid conduit, minimum 18 inches for direct burial, etc.). NEC 225.32 and 225.40 require a ground rod at the garage and proper bonding of all metal. You will need to file an electrical permit and possibly a building permit for the electrical infrastructure. The scope includes: (1) the feeder from the house main panel to the garage, (2) the main disconnect at the garage (can be the sub-panel itself or a separate disconnect switch), (3) the sub-panel, (4) the ground rod and grounding conductor, and (5) all branch circuits served from the sub-panel. This is not a weekend DIY project in any state — hire a licensed electrician. They will pull the permit and manage the inspections. Prepare for 3–6 weeks from filing to final inspection. Cost: $150–$400 for the permit alone, plus your contractor's labor and materials.
Installing a 30-amp sub-panel in your detached tiny home (guest structure) on the same property, with the same main panel as the house
You need a permit. Even though the amperage is low (30 amps), the fact that it's a new sub-panel in a separate structure makes this a permit-required project. You will be running a feeder from the main panel to the tiny home and installing a sub-panel there. The same NEC 225.30–225.40 rules apply: you need a ground rod at the tiny home, bonded to the sub-panel. You also need to confirm whether your main panel has capacity to send a 30-amp feeder without exceeding the total service amperage of the house. For example, if your house has 200-amp service and is already drawing close to 200 amps of continuous load, a 30-amp addition might push you over or require careful load management. The building department may ask you to provide a load calculation to prove that the main service is adequate. File an electrical permit, include a site plan, include a one-line diagram of the main panel and the feeder to the tiny home, and show the ground rod location at the tiny home. Plan for 2–4 weeks approval, plus 1–2 inspections. Cost: $100–$200.
What you'll need to file and who can pull the permit
| Document | What it is | Where to get it |
|---|---|---|
| Electrical Permit Application | The formal application form filed with your building department or electrical inspection agency. It will ask for basic project info (address, description, estimated cost), the applicant's name and license number (if required), and a brief scope of work. | Your local building department's website or office. Most jurisdictions post the form online; some still require you to pick it up in person or request it by email. A few jurisdictions have moved to online portals where you fill out the application digitally. |
| One-Line Diagram (or Single-Line Diagram) | A schematic drawing showing the main electrical panel, the feeder from the main panel to the sub-panel, the main breaker size in the sub-panel, and the branch circuits served from the sub-panel. It doesn't need to be to scale or professionally drawn — a clear hand-drawn diagram is usually acceptable. The inspector uses this to verify that breaker sizes match wire gauges and that load calculations are reasonable. | You draw this yourself or your electrician provides it. Templates are available online; the NEC has example diagrams in Article 408. |
| Feeder Calculation Sheet (or Load Calculation) | A sheet showing the size of the wire, conduit, and breaker feeding the sub-panel. For a 100-amp sub-panel, you might use #2 copper or #1/0 aluminum. For a 200-amp sub-panel, #2/0 or #3/0. The calculation sheet shows that the wire is sized correctly for the breaker and the distance from the main panel. This is especially important for detached structures because longer runs (say, 100 feet of feeder from house to garage) require larger wire. | Your electrician provides this, or you can calculate it using NEC Tables 310.15(B)(2)(a) (ampacity of conductors) and 250.66 (size of grounding electrode conductor). Online calculators exist, but the NEC tables are the authoritative source. |
| Site Plan (for detached structures) | A bird's-eye-view drawing showing your house, the detached structure (garage, shed, etc.), the feeder route between them, the location of the main panel in the house, and the location of the sub-panel and ground rod at the detached structure. Approximate distances are fine; the inspector wants to know whether the feeder is routed safely (not under driveways, not exposed in high-traffic areas, etc.). | You draw this or your electrician provides it. A sketch on graph paper is sufficient. |
| Scope of Work or Project Description | A brief written description of what you're doing: 'Install a 100-amp sub-panel in basement to serve workshop circuits' or 'Install a 60-amp sub-panel in detached garage to power EV charger and workshop equipment, including new feeder from main panel and ground rod at garage.' This helps the permit reviewer understand the scale and complexity. | You write this on the permit application or as an attachment. |
| Proof of Contractor License (if required) | A copy of the licensed electrician's electrical license if your jurisdiction requires one. Some states require the license to be on file with the building department; others just ask for the license number on the application. Ask your building department whether they need a copy. | Your electrician provides this, or you can request a copy from your state's licensing board (typically the Department of Labor or State Board of Professional Regulation). |
Who can pull: In most states, a licensed electrician or master electrician must pull the electrical permit and be the responsible party on the job. In a handful of states (Minnesota, Texas, and a few others), a homeowner can pull an electrical permit for owner-occupied residential work, including sub-panels, and do the work themselves. However, most states prohibit homeowner-pulled electrical permits for sub-panels specifically, even if they allow it for simpler work. A few jurisdictions allow the homeowner to be the applicant but require that a licensed electrician sign off on the work before inspection. Call your building department and your state's licensing board to confirm the rules for your jurisdiction. If you're hiring a contractor, this doesn't matter — they will pull the permit as part of their scope. If you're planning to do the work yourself, ask the building department directly: 'Can a homeowner pull an electrical permit for a sub-panel installation and do the work themselves in this jurisdiction?' Get a definitive yes or no before you proceed.
Why sub-panel permits get rejected and how to fix them
- Application filed under wrong permit type (e.g., building permit instead of electrical permit).
Sub-panel work is electrical work, not general building work. File under the electrical permit category, not building permit. If your jurisdiction uses an online portal, select 'Electrical – Subpanel Installation' or 'Electrical – Service and Distribution' from the dropdown. If you file in person, ask the intake clerk, 'Is this the right form for an electrical sub-panel permit?' The wrong form can cause a 1–2 week delay while the application is rerouted. - One-line diagram is missing or too vague. The reviewer can't tell what breaker size feeds the sub-panel, what wire size is used, or what circuits are served from the sub-panel.
Redraw or ask your electrician to redraw the one-line diagram with all the details: main panel amperage, main breaker in the main panel (e.g., '30A'), feeder size (e.g., '#10 Cu, 30A'), sub-panel amperage (e.g., '100A'), main breaker in the sub-panel (e.g., '100A'), and a list of branch circuits with their breaker sizes and loads. This is the most common reason for rejection. The reviewer needs to see that the design is safe and code-compliant, and they can't do that from a vague sketch. - Missing ground rod detail for a detached structure sub-panel. The application shows the sub-panel but doesn't mention the ground rod or bonding.
For any sub-panel in a detached building (garage, shed, guest house), your scope must explicitly include: (1) a ground rod at the detached structure (minimum 8 feet long, per NEC 250.52(a)(5)), (2) a grounding electrode conductor bonding the rod to the sub-panel enclosure, and (3) a grounding conductor bonding the rod to the neutral/ground bus in the sub-panel (if the sub-panel is not the main service disconnect). Resubmit with a site plan showing the ground rod location and a one-line diagram showing the bonding. If the building department's inspector arrives on-site and there is no ground rod, the job fails inspection and you'll have to install one before re-inspection. - Feeder wire size does not match breaker size or distance. For example, a 60-amp breaker feeding a 100-foot run to a detached garage with #10 wire (rated for 30 amps).
Use NEC Table 310.15(B)(2)(a) to confirm the ampacity of the wire at the breaker size and at the feeder distance. A 60-amp breaker requires at minimum #8 copper or #6 aluminum (both rated for 50+ amps). If the run is 100 feet, you must upsize the wire to account for voltage drop — typically #6 copper or #4 aluminum for a 60-amp, 100-foot run. Resubmit with a corrected feeder calculation sheet showing the correct wire size. Your electrician should do this calculation; if you're unfamiliar with the tables, ask them to review the spec before filing. - Scope drawing references wrong code edition. For example, the application cites NEC 2017, but your state has adopted the 2023 NEC.
Confirm which code edition your state and local jurisdiction have adopted. Most states are on the 2020 or 2023 NEC as of 2024. Update your application to reference the correct edition. The NEC article numbers (225, 408, etc.) usually don't change between editions, so your technical details should still be correct — this is mainly a paperwork fix. Ask your building department: 'Which edition of the NEC does this jurisdiction use?' — they'll tell you. - Electrician's license number is missing or incorrect. The application requires the license number of the responsible party, but it's blank or wrong.
Obtain the correct license number from your electrician. In most states, you can verify it online through your state's licensing board website (search for 'electrical contractor license [state]'). If you're doing the work yourself and your state allows homeowner permits, use your name on the application instead. If you're unsure who should be listed, call the building department: 'Should the electrician's license number or the homeowner's name go on this application?' - Project cost is underestimated, triggering a review for undervaluation or fraud. For example, listing a full 200-amp sub-panel installation at $500 when typical cost is $3,000–$5,000.
Estimate the project cost honestly, including materials and labor. If you're unsure, ask your electrician for an estimate. The building department uses the valuation to assess fees and (in some jurisdictions) to flag potential safety issues. If you drastically undervalue the project, the department may reject the application and ask for a revised estimate with a quote from the contractor. It's not worth the hassle — estimate correctly upfront.
Sub-panel permit costs and fee basis
Sub-panel permit fees range widely depending on your jurisdiction and the scope of work. Some building departments charge a flat fee for electrical permits (e.g., $100 for any electrical permit, $200 for complex work). Others charge a percentage of project valuation, typically 1.5–2%. A few jurisdictions have tiered fees based on amperage (e.g., $50 for a sub-panel under 100 amps, $100 for 100–200 amps, $150 for over 200 amps). You'll need to contact your building department to get the exact fee for your project. When you call, ask: 'What is the permit fee for a [your amperage]-amp sub-panel installation? Is it a flat fee, a percentage of project cost, or based on amperage?' Also ask whether there are separate fees for plan review, inspection, or reinspection. Some jurisdictions bundle everything into the base fee; others charge separately. Plan check typically takes 1–3 weeks and is usually included in the base fee. If the reviewer finds issues with your drawings, you resubmit at no extra charge. Inspection is usually included in the permit fee as well — the first inspection is free; reinspection if work fails is sometimes free or sometimes $50–$100 per additional visit. Once you know the base fee, add any reinspection costs if the job is complex.
| Line item | Amount | Notes |
|---|---|---|
| Flat-fee jurisdiction (e.g., Madison, Denver) | $75–$200 | Single fee covers permit, plan review, and first inspection. Reinspection may cost $50–$100 extra if needed. Ask your building department for the specific flat rate. |
| Percentage-of-valuation jurisdiction (e.g., California, Florida) | $100–$500 | Fee is 1.5–2% of estimated project cost. A 100-amp sub-panel in a basement might be valued at $3,000–$4,000 (materials + labor), yielding a fee of $45–$80. A 200-amp sub-panel in a new detached garage might be valued at $8,000–$12,000, yielding a fee of $120–$240. Confirm the percentage rate with your building department. |
| Tiered-by-amperage jurisdiction | $50–$250 | Example: $50 for under 100 amps, $100 for 100–200 amps, $150 for over 200 amps. Some jurisdictions add extra fees for detached structures. Ask whether your project qualifies for a lower tier. |
| Plan review fee (if separate) | $0–$100 | Some jurisdictions charge a separate plan review fee upfront. This is often waived or bundled into the permit fee. Confirm whether it's separate before you file. |
| Reinspection fee (if work fails initial inspection) | $0–$150 | If the inspector finds code violations (e.g., missing ground rod, wrong wire size, improper bonding) on the first inspection, you'll be asked to fix them. Some jurisdictions charge a reinspection fee; others include unlimited reinspections in the permit. Ask upfront whether reinspections are free or charged. |
| Expedited review (if offered) | $100–$300 | A few jurisdictions offer expedited plan review (3–5 days instead of 2–3 weeks) for an extra fee. Use this only if you're in a time crunch; it's not necessary for most projects. |
Common questions
Do I need a permit if I'm just replacing the sub-panel with an identical new one?
Usually yes, sometimes no — it depends on your jurisdiction. Some building departments exempt a like-for-like replacement of an existing sub-panel in the same location with the same amperage, especially if you're not changing the feeder or breaker. Others require a permit even for replacements because removing and reinstalling a panel involves electrical work that must be inspected. The only way to know is to call your building department and describe the project. Ask: 'I have an existing 200-amp sub-panel in my basement. I want to replace it with a new 200-amp panel of the same model in the same location, with no other changes. Do I need a permit?' Get the answer in writing if possible. Even if you don't need a permit, you'll likely need a licensed electrician to do the work — homeowners are generally not allowed to remove and reinstall sub-panels.
Can I pull the electrical permit myself, or does it have to be done by a licensed electrician?
This depends entirely on your state. In a handful of states (Minnesota, Texas, and a few others), a homeowner can pull an electrical permit for owner-occupied residential work and do the labor themselves, including sub-panels. In most states, a licensed electrician or master electrician must pull the permit and be the responsible party. In some states, the homeowner can be the applicant but a licensed electrician must sign off on the work before inspection. Check your state's rules by calling your state's licensing board (typically the Department of Labor or Electrical Licensing Board) or your local building department. If you're hiring a contractor, ask them to pull the permit as part of their scope — this is standard practice and saves you the hassle.
What's the most common mistake people make when filing a sub-panel permit?
Forgetting the ground rod for a detached structure sub-panel. The NEC requires that any sub-panel in a detached building (garage, shed, barn, tiny home, etc.) have its own ground rod, bonded to the sub-panel. Many homeowners and unlicensed installers either skip this step entirely or bond it incorrectly (e.g., bonding ground and neutral at the sub-panel, which is code-compliant at the main service but forbidden at a detached sub-panel). When the building inspector arrives on-site and there's no ground rod, the job fails inspection. The second most common mistake is undersizing the feeder wire for the distance. A 60-amp feeder running 100 feet from the house to a garage needs larger wire than a 60-amp feeder running 20 feet — but many people use the same wire size regardless. Use NEC Table 310.15(B)(2)(a) to confirm wire size, accounting for distance and voltage drop. If you're unsure, ask your electrician to do the calculation.
How long does it take to get a sub-panel permit approved?
Typically 1–4 weeks from filing to approval. Most building departments process electrical permits in 2–3 weeks if the application is complete and the inspector doesn't find issues. If your application is missing details (e.g., no one-line diagram, vague scope), the department will contact you and ask for revisions — this adds 1–2 weeks. Once the permit is approved, you have a window (usually 180 days to one year) to start and finish the work. The on-site inspection typically happens within a few days of when you call for it, but it must happen after the sub-panel is installed and roughed in but before drywall or permanent cover. Plan for 2–4 weeks from filing to approval, then schedule the inspection when the electrician is ready.
Do I need a separate permit for a detached structure sub-panel, or is it part of the building permit?
You need an electrical permit for the sub-panel itself. If you're also building a new detached structure (new garage, new shed), you'll file a separate building permit for the structure and an electrical permit for the sub-panel and wiring. The building permit covers the framing, roof, doors, windows, etc.; the electrical permit covers the service and distribution. File both, but they are separate applications with separate timelines and fees. If you're adding a sub-panel to an existing detached structure (e.g., an old garage that never had power), you just need an electrical permit — no building permit. Ask your building department which permits you need: 'I want to install a sub-panel in my detached garage. Do I need a building permit or just an electrical permit?' They'll tell you.
Will the inspector require an EGC (equipment grounding conductor) between the main panel and the sub-panel?
Yes, always. The equipment grounding conductor (EGC) is the green wire or bare copper wire that runs alongside the feeder from the main panel to the sub-panel. It bonds the sub-panel enclosure to the ground bus at the main panel, providing a path for fault current if there is a short. The NEC requires an EGC for any feeder, including sub-panel feeders. Use the same conduit or cable jacket as the feeder (e.g., if you use individual THHN wires in conduit, add a bare copper EGC in the same conduit). The size of the EGC is determined by NEC Table 250.122 based on the size of the feeder breaker. For a 60-amp feeder, you need at least a #10 EGC. For a 100-amp feeder, at least #8. For a 200-amp feeder, at least #6. The inspector will check this on-site. It's a common oversight, so make sure your electrician knows to include it.
What happens if I install a sub-panel without a permit?
The risks are substantial. If an inspector or code enforcement officer discovers unpermitted electrical work, you can be fined $500–$5,000+ depending on your jurisdiction. More importantly, unpermitted work voids your homeowner's insurance claim if there's an electrical fire, electrocution, or equipment damage. Selling the home becomes complicated — the buyer's lender or inspector may discover the unpermitted work and require you to remove the sub-panel or bring it into compliance before closing. You'll then have to file a permit retroactively, which often triggers a full re-inspection and possible code violations if the work doesn't meet current code. If someone is injured due to the electrical hazard, you could face personal liability. A sub-panel is not a cosmetic upgrade — it's a safety-critical system. The permit fee ($75–$250) is cheap insurance compared to the risk. File the permit.
Do I need to provide a load calculation when I file the permit?
In most jurisdictions, a basic load calculation or feeder-sizing calculation is required or strongly recommended. For a new sub-panel, the inspector needs to confirm that the feeder breaker size and wire size match the load you're serving. For example, if you're installing a 100-amp sub-panel to serve a basement workshop, the inspector will want to see that you've calculated the expected load (lights, outlets, machinery, etc.) and confirmed that 100 amps is adequate. For simple residential sub-panels (100 or 150 amps), a rough calculation is usually sufficient: list the circuits you plan to serve, estimate the load on each, and sum them to confirm that the sub-panel amperage is adequate. For more complex installations (e.g., a sub-panel serving multiple buildings or high-load equipment), a formal load calculation per NEC Article 220 is required. Your electrician will do this. If you're unsure whether you need a formal calculation, ask your building department when you file.
Can a sub-panel be the main service disconnect for a detached structure?
Yes, with conditions. NEC 225.33 allows a sub-panel to serve as the main service disconnect for a detached building, but it must be the first disconnect in the building. This means that all circuits in the detached structure must be fed from that sub-panel, and the sub-panel itself must be the only breaker between the feeder and the circuits. In practical terms, this is common for small detached garages, sheds, and guest houses. The sub-panel is installed as the service entrance, and all circuits branch from it. For larger detached structures, you might have a separate meter and a main service panel at the structure instead of a sub-panel. The distinction is technical but important for code compliance. If you're not sure whether a sub-panel or a separate service panel is right for your structure, ask your electrician or building department. The permit application will specify which one is being installed, and the inspector will verify it on-site.
If I hire a licensed electrician to install the sub-panel, do I still need to be involved in the permit process?
Typically no. Most licensed electricians handle the entire permit process as part of their scope: they file the permit application, provide the required drawings, coordinate with the building department, and schedule inspections. You just pay them and let them manage the permitting. However, it's a good idea to confirm this with the electrician upfront: 'Do you handle all the permits and inspections, or do I need to do any of that?' A reputable contractor will handle it all. If you're the property owner, you may need to sign the permit application or provide proof of property ownership, but the electrician will tell you what's needed. Stay in touch with the electrician about the permit timeline so you know when inspections will happen.
Ready to file for your sub-panel permit?
Start by calling your local building department or electrical inspection agency. A 5-minute conversation will confirm whether you need a permit, what documents to file, the fee, and the timeline. Have your project details ready: the amperage of the sub-panel, where it's located (same building or detached structure), and what it will serve. If you're hiring a licensed electrician, they can usually handle the permitting for you. If you're planning to do the work yourself, confirm that you're eligible to pull an electrical permit in your state. Once you know what you need to file, gather the one-line diagram, feeder calculation, and scope description — then submit. Most jurisdictions process sub-panel permits in 2–4 weeks and schedule inspections within days of approval.
Related permit guides
Other guides in the Electrical category: