2021 IRC Chapter 36
The service is everything between the utility's conductors and the dwelling's main disconnect: the overhead service drop or underground service lateral, the service-entrance conductors, the meter, and the service equipment where the main disconnect lives. This lesson covers how large a service has to be, where its disconnect can go and how it has to be marked, the clearances an overhead drop has to keep above roofs, grade, driveways, and windows, and the routing rules for the conductors that make up the service itself. These are among the first things an inspector checks on a rehab or new infill job, because a service that is undersized, poorly located, or run with too little clearance drives the price and the timeline of everything else in the project.
Conductors run overhead from the utility pole to the building are the service drop; conductors run underground are the service lateral. Both are typically utility-owned up to the service point, where the utility connects to the premises wiring. From there, service-entrance conductors carry power to the service equipment, where the main disconnect and the grounding system come together, covered fully in Lesson 3. Service conductors are the one set of conductors in the house with no overcurrent protection ahead of them; everything downstream of the main disconnect, a feeder or a branch circuit, is protected by a breaker or fuse. That single distinction, protected or not, is the cleanest way to decide whether a given run of conductors is a service or a feeder.
A one-family dwelling requires a service of at least 100 amperes, 3-wire (E3602.1); that is a code floor, not a design target, and GCHS commonly sees 150 A and 200 A services once electric ranges, heat pumps, and EV charging are accounted for. The actual size required comes from the load calculation in Table E3602.2: 3 volt-amperes per square foot for general lighting and receptacles, plus 1,500 volt-amperes for each small-appliance and laundry circuit, plus the nameplate rating of fixed appliances such as ranges and dryers. The first 10,000 volt-amperes of that subtotal count at 100 percent and the rest at 40 percent, then the largest of the cooling or heating loads is added, and the total is divided by 240 volts to get amperes. For GCHS estimating purposes, the load calculation, not just the panel's amperage label, is what determines whether a service is adequate; a 100 A panel on a house with electric heat, a range, and a large well pump can be undersized even though the label reads "100 A."
The service disconnecting means must be installed at a readily accessible location, either outside the building or inside nearest the point where the service conductors enter (E3601.6.2), so that the run of unprotected service conductors inside the structure stays as short as possible. Each service normally has only one disconnecting means. Up to six are allowed where they are installed as separate enclosures, separate panelboards, or separate compartments of a metering center, and multiple disconnects have to be grouped (E3601.7), the historical "rule of six," so that a responder can kill everything with at most six motions. The disconnect has to be permanently marked as a service disconnect (E3601.6.1), and, like overcurrent devices generally, it is not permitted to be installed in a bathroom. In a two-family dwelling, each occupant must have access to the disconnect serving the dwelling unit in which they reside, so a disconnect that only the other tenant can reach does not comply.
One- and two-family dwelling services must also have an emergency disconnect in a readily accessible outdoor location, marked with wording such as EMERGENCY DISCONNECT, SERVICE DISCONNECT, so firefighters and other first responders can de-energize the dwelling from the yard without entering a burning or flooded structure. This sometimes gets described as a newer requirement jurisdictions are still catching up to, so it is worth stating plainly: it first appeared in the 2020 NEC at Section 230.85, and it is already part of the 2021 IRC's own text at E3601.8, not something added only in a later IRC edition. A Texas city that has adopted the 2021 IRC is enforcing this requirement now, though GCHS still confirms the specific edition and any local amendments the permitting jurisdiction has adopted before assuming a single rule applies everywhere.
Every service supplying a one- or two-family dwelling unit must also have a surge-protective device, Type 1 or Type 2, either built into the service equipment or installed immediately adjacent to it (E3606.5). Where the service equipment is replaced, the requirement applies to the new equipment (E3606.5.3), so a panel change on a rehab job picks up an SPD line item.
| Location of overhead service conductors | Minimum clearance |
|---|---|
| Service entrance drip loop and pedestrian-only areas (conductors cabled with a grounded bare messenger) | 10 feet |
| Above residential property and driveways | 12 feet |
| Above public streets, alleys, roads, or parking areas subject to truck traffic | 18 feet |
| From the sides and bottom of a window that opens, and from doors, porches, decks, stairs, and balconies | 3 feet |
The point where the service conductors attach to the building must itself be at least 10 feet above finished grade, a separate check from the clearance the span keeps as it crosses a driveway or street. Above a roof, the general vertical clearance is 8 feet (E3604.2.1), maintained for 3 feet in all directions beyond the roof's edge, not just at the ridge; a drop that clears the ridge but sags within 3 feet of the eave can still fail. Where the roof slope is at least 4 inches of rise per 12 inches of run, that clearance may be reduced to 3 feet, since nobody is casually walking or storing material on a roof that steep. The window rule is measured from the sides and bottom of a window that opens, so the conductors to worry about are the ones passing beside or below it. The final span of a drop attached to the side of a building is exempt from the 3-foot-beyond-the-edge rule (E3604.2.1 Exception 4).
Because service conductors have no overcurrent protection ahead of them, the code keeps them short and separate. The service disconnect goes outside or nearest the point where the conductors enter (E3601.6.2), and service conductors supplying one building may not pass through the interior of another building or structure (E3601.3). Service conductors also cannot share a raceway or cable with non-service conductors such as branch circuits (E3601.4), since an unprotected fault between the two would be catastrophic; the exceptions are grounding electrode conductors, supply-side bonding jumpers, and load management control conductors that have overcurrent protection. Splices in service-entrance conductors are permitted only inside enclosures or, if directly buried, with listed underground splice kits, and power distribution blocks must be listed (E3605.3), never an improvised taped joint in the open. Service-entrance cable is supported within 12 inches of every service head, gooseneck, or enclosure connection and at intervals of not more than 30 inches (E3605.7).
Dwelling services and feeders that carry the entire load are permitted an ampacity of not less than 83 percent of the service rating (E3603.1.1 and Table E3603.1.1). In practice this produces a small set of pairings worth memorizing: a 100 A service is commonly run with 4 AWG copper or 2 AWG aluminum, and a 200 A service with 2/0 AWG copper or 4/0 AWG aluminum, aluminum running two sizes larger than copper for the same job. These are the numbers GCHS estimators check first against a panel's rating.
A worked example: a house is being upgraded to a 100 A service. Under the 83 percent dwelling allowance, the conductors need an ampacity of at least 100 times 0.83, or 83 amperes. Looking at the 75-degree-C column of Table E3705.1, the column that applies where the service equipment is listed and identified for 75-degree-C conductors (E3705.4.1), 4 AWG copper is rated 85 amperes, which clears the 83-ampere floor with 2 amperes to spare. In the 60-degree-C column the same conductor is only 70 amperes, which is why the equipment listing matters. That is exactly why 4 AWG copper is the number attached to a 100 A dwelling service throughout this course.
In the field
A recurring finding on GCHS rehab estimates is a meter and service disconnect mounted tight between a downspout and a hose bib at the corner of the house, with barely 20 inches of clear space in front of the panel. Working space applies outdoors exactly as it does in a basement: 36 inches deep and 30 inches wide (or the equipment width, whichever is greater), and neither a downspout nor a hose bib is allowed to sit inside that zone. Catching this at the estimating stage, before the utility resets the meter in the same crowded spot, is far cheaper than relocating a live service after the fact.
1. The minimum service size for a one-family dwelling is:
2. Overhead service conductors crossing a residential driveway must clear it by at least:
3. An inspector arrives at a rehab where the meter and main disconnect are crowded between a downspout and a hose bib, leaving about 20 inches of clear space in front of the equipment. What should the inspector check first?
4. Where a service uses more than one disconnecting means, the maximum number permitted, grouped together, is:
5. A service disconnect is proposed for installation inside a first-floor bathroom of a rehabbed duplex. This is:
6. The outdoor emergency disconnect required for one- and two-family dwelling services:
7. Conductors running from the main panel to a subpanel in a detached garage, protected by a breaker at the main panel, are properly called:
8. Overhead conductors run from a utility pole to a house are called the service ______, while conductors run underground to the house are the service ______.
9. Where a roof slope is at least 4 inches of rise per 12 inches of run, the required overhead clearance above the roof may be reduced to:
10. An inspector finds service-entrance conductors sharing a raceway with branch-circuit conductors feeding household receptacles. The concern is:
11. Applying the dwelling service and feeder 83 percent allowance, the smallest copper conductor commonly used for a 100-ampere single-phase dwelling service is:
12. Splices in service-entrance conductors are:
13. In a two-family dwelling, the service disconnect location rule (E3601.6.2) also requires that:
14. An inspector must decide whether a run of conductors is a service or a feeder. The most useful question to ask is: