2023 NEC Article 230
The service is where the utility's power becomes the building's power, and every later rule in the installation depends on getting it right. Article 230 covers how many services a building may have, how the conductors are run and how high they must be, where the disconnect goes, how it is rated and protected, and when the service needs ground-fault protection. This lesson walks the service from the pole to the main disconnect. Load calculations are Lesson 4, overcurrent devices are Lesson 6, and grounding of the service is Lesson 7. Local adoption governs which NEC edition applies (see Lesson 1), and the serving utility sets its own metering and meter-base requirements.
A building or structure is supplied by only one service, unless one of the exceptions in Section 230.2 applies (2023 NEC 230.2). The additional services allowed as special conditions are for fire pumps, emergency systems, legally required standby, optional standby, interconnected power production sources, and systems designed for multiple sources for reliability (230.2(A)). Additional services may be allowed by special permission in a multiple-occupancy building with no room for common service equipment, or in a building large enough to need two or more (230.2(B)). Capacity can also justify another service where the requirement exceeds 2000 A at 1000 V or less (230.2(C)), and different voltages, frequencies, phases, or rate schedules allow additional services (230.2(D)). Where more than one service, feeder, or branch circuit supplies a building, a permanent plaque or directory at each service disconnect location must show the others and the area each serves (230.2(E)).
Each service drop or lateral supplies only one set of service-entrance conductors (230.40), and service conductors may not pass through the interior of another building (230.3).
Overhead service conductors may not be readily accessible, and the minimum clearances depend on what is underneath (230.24). Heights are measured from final grade or another accessible surface.
| Area under the conductors | Minimum clearance |
|---|---|
| Service entrance, drip loop, and pedestrian-only areas (cabled on a grounded bare messenger, 150 V or less to ground) | 10 ft |
| Residential property and driveways, and commercial areas with no truck traffic, 300 V or less to ground | 12 ft |
| The same areas where the voltage to ground exceeds 300 V | 15 ft |
| Public streets, alleys, roads, parking areas with truck traffic, and driveways on other than residential property | 18 ft |
| Above a roof surface | 8 ft 6 in, kept 3 ft out from the roof edge |
Notice how the commercial lot changes the answer. The same 208Y/120 V service drop over a clinic's customer parking needs 12 ft, and over the delivery lane behind the building it needs 18 ft. A roof over which pedestrians or vehicles travel uses the ground clearances instead of the roof clearance. There are reductions above roofs at 300 V or less between conductors for steeper roofs (4 in 12 or more) and for roof overhangs under stated limits (230.24(A)). Open service conductors and cable without an outer jacket must stay 3 ft from operable windows, doors, porches, balconies, ladders, stairs, and fire escapes (230.9(A)), and overhead conductors may not run beneath openings through which materials are moved, which matters at loading docks (230.9(C)). A service mast may support only the power conductors and must be strong enough or braced (230.28).
Service conductors must carry the load calculated in Article 220 and have enough mechanical strength (230.23(A)). The overhead minimum size is 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. A smaller conductor, down to 12 AWG hard-drawn copper, is allowed only for limited loads on a single branch circuit, such as a controlled water heater (230.23(B)). Conductor sizing itself is covered in Lesson 8.
The building needs a means to disconnect all ungrounded conductors from the service conductors (230.70). It must be at a readily accessible location, either outside the building or inside, nearest the point where the service conductors enter (230.70(A)(1)). It may not be in a bathroom (230.70(A)(2)). Where a remote control device operates the disconnect, the disconnect itself still has to follow the same location rule (230.70(A)(3)). Each service disconnect is permanently marked to identify it as a service disconnect (230.70(B)). The equipment must be marked as suitable for use as service equipment and be listed or field evaluated (230.66(A)). A meter socket is not service equipment, but it must be listed and rated for the service voltage and current (230.66(B)).
Each service has one disconnecting means, unless the two-to-six rule applies (230.71). Two to six disconnects are allowed for a service. They may be separate enclosures with a main in each, panelboards with a main, metering centers, and similar arrangements (230.71(B)). They must be grouped, and each is marked to show the load it serves (230.72(A)). Disconnects for fire pumps, emergency, and standby services are placed remote from the normal group so one event cannot interrupt both (230.72(B)). In multiple-occupancy buildings each tenant must be able to reach the tenant's own disconnect, except where building management provides service and maintenance under continuous supervision (230.72(C)). Equipment disconnects built into listed equipment for power monitoring, surge protection, and the ground-fault control circuit do not count toward the six (230.71(A)). Where several disconnects are used, their combined rating may not be less than the rating 230.79 requires (230.80).
The disconnect rating may not be less than the calculated load, and never less than 60 A for an ordinary installation (15 A for one branch circuit, 30 A for two circuits, and 100 A for a one-family dwelling) (230.79). Each ungrounded service conductor needs overload protection at a rating not above the conductor ampacity, where the next-size-up rule of 240.4(B) and the standard ratings of 240.6 may be used (230.90(A)). The service overcurrent device must be built into the disconnect or immediately adjacent to it, and where fuses are used, the disconnect sits ahead of them on the supply side (230.91).
A solidly grounded wye service of more than 150 V to ground and not over 1000 V phase-to-phase must have ground-fault protection of equipment for each service disconnect rated 1000 A or more (230.95). The rating means the largest fuse that can be installed or the highest continuous trip setting the installed breaker can be adjusted to. It does not apply to a disconnect for a continuous industrial process where an unplanned shutdown creates added hazards. The protection must open all ungrounded conductors of the faulted circuit, with a maximum setting of 1200 A and a maximum delay of one second at ground-fault currents of 3000 A or more (230.95(A)). It must be tested on site by primary current injection, with a written record for the authority having jurisdiction (230.95(C)). It only protects the load side of the sensor, so downstream selectivity should be reviewed.
Worked example: a small community hospital annex has a calculated load of 700 kVA on a 480Y/277 V three-phase service. The current is 700,000 / (1.732 x 480) = 842 A. The disconnect may not be rated below 842 A, and 800 A is the last standard rating below it, so the next standard device is 1,000 A (Table 240.6(A)). The service is a solidly grounded wye at 277 V to ground, which is over 150 V, and the disconnect is 1,000 A, so ground-fault protection is required. Above 800 A the next-size-up rule does not apply, so the conductors must carry at least the device rating (240.4(C)). The same 700 kVA on 208Y/120 V would be 1,943 A. That service is only 120 V to ground, so 230.95 does not apply, but the disconnect would be about 2,000 A, the top of what a single service is normally allowed (230.2(C)(1)).
Surge-protective devices are required at services supplying dwelling units, dormitory units, guest rooms and suites of hotels and motels, and patient sleeping areas of nursing homes and limited-care facilities (230.67(A)). They must be part of the service equipment or adjacent, be Type 1 or Type 2, and have a nominal discharge current of at least 10 kA (230.67(B), (C), (E)). An ordinary office or retail building is not on that list. The emergency disconnect in 230.85 is for one- and two-family dwelling units only, so it does not apply to a commercial service.
In the field
A GCHS crew is converting an old warehouse into a small community clinic and rehab office. The utility will feed it overhead from a pole across the rear delivery lane. The inspector stands in the lane and measures the lowest point of the drop against the 18 ft truck-lane line, not the 12 ft line used in the front lot. The main disconnect has been mounted inside a janitor closet that also holds the restroom water heater, so the inspector checks that it is nearest the point of entrance, readily accessible, not in a bathroom, and marked as a service disconnect. The gear nameplate shows 480Y/277 V and a 1,200 A frame with an adjustable trip, so the inspector asks for the ground-fault settings and the written primary-injection test record.
1. A community center with a single-service building adds a fire pump. Under 2023 NEC 230.2(A), is a separate service for the fire pump allowed?
2. A multi-tenant commercial building has no available space for common service equipment for all tenants. Under 230.2(B), how may an additional service be allowed?
3. Overhead 208Y/120 V service conductors cross the rear delivery lane of a commercial building that is used by trucks. What minimum clearance from final grade does 230.24(B) require at the lowest point?
4. Overhead 208Y/120 V service conductors pass over the customer parking lot of a small clinic. No trucks use the lot. What minimum clearance applies under 230.24(B)?
5. A 208Y/120 V service drop cabled with a grounded bare messenger passes over a walkway used only by pedestrians. What minimum clearance from the walkway surface is required?
6. Overhead service conductors cross a flat commercial roof that is not used by pedestrians or vehicles. What minimum vertical clearance above the roof surface does 230.24(A) require, and how far from the roof edge is it kept?
7. An inspector finds open service conductors installed 18 inches from an operable window on the side of a commercial building. What does 230.9(A) require?
8. A commercial building's service enters on the north wall. Where does 230.70(A)(1) allow the service disconnect to be installed?
9. During a rehab of a two-story office, the electrician proposes mounting the main disconnect inside the first-floor restroom, since it is nearest where the conduit comes in. What does 230.70(A)(2) say?
10. A main breaker in a new office building has no label at all. Which requirement of 230.70(B) is not met?
11. A strip center owner wants seven separate tenant service disconnects grouped on one service. What does 230.71(B) allow?
12. A 480Y/277 V three-phase service has a main breaker that is adjustable up to 1,200 A. Does 230.95 require ground-fault protection of equipment?
13. A hotel laundry building has a 208Y/120 V three-phase service with a 2,000 A main disconnect. Does 230.95 require ground-fault protection of equipment at the service?
14. Which ground-fault protection setting complies with 230.95(A) on a 480Y/277 V, 1,200 A service disconnect?