3.1 Service Size, Rating & Installations (0201)
Key Takeaways
- NEC 230.2 permits only one service per building unless an exception applies (fire pumps, emergency/standby systems, multiple-occupancy buildings, capacity over 2000 A at 1000 V or less, or different voltage/phase/usage).
- 230.71(B) permits two to six service disconnects, but since the 2020 NEC they may no longer share one enclosure: each must be in its own enclosure, its own panelboard, its own barriered switchboard section, or its own switchgear/metering-center compartment.
- 230.79 sets minimum service-disconnect ratings: 15 A for a one-circuit installation, 30 A for not more than two 2-wire branch circuits, 100 A 3-wire for a one-family dwelling, and 60 A for all other installations.
- 230.42(A)(1) requires service-entrance conductor ampacity of not less than 125% of the continuous load plus 100% of the non-continuous load, mirroring the feeder rule in 215.2/215.3.
- 230.95 requires ground-fault protection of equipment only on solidly grounded wye services of MORE than 150 volts to ground but not over 1000 volts phase-to-phase, for each service disconnect rated 1000 A or more — so a 208Y/120 V service is exempt no matter how large it is.
Service Conductors: Drop, Lateral, and Entrance
NEC Article 230 governs services — the conductors and equipment that deliver power from the serving utility to the premises wiring system. Inspectors must distinguish the segments because each carries different installation rules:
- Service drop (230.2, 230.24) — overhead conductors from the utility pole to the service point.
- Service lateral (230.2, 230.30) — underground conductors from the utility transformer to the service point.
- Service-entrance conductors (230.40, 230.41) — conductors from the service point to the service disconnecting means; may be installed as open wire on insulators, in raceway, or as Type SE cable.
The service point is the demarcation between utility-owned conductors and premises wiring. Everything load-side of the service point falls under NEC Article 230.
Number of Services and Disconnects (230.2, 230.71)
230.2 permits each premise to be supplied by only one service unless an exception applies. Recognized exceptions include:
- Fire pumps (with limited service so the fire pump OCPD may be set higher)
- Multiple-occupancy buildings where each occupant has a separate service
- Capacity requirements exceeding 2000 A at 1000 V or less
- Different voltage, phase, or usage (e.g., normal vs. emergency/standby systems)
230.71(B) permits two to six service disconnects for each service. This is the rule that changed most recently and is heavily tested: for decades the Code allowed up to six switches or circuit breakers inside a single enclosure, and the 2020 NEC deleted that allowance because energized busbars remain exposed inside the enclosure even when all six handles are off. Under the current rule the two to six disconnects must be a combination of:
- Separate enclosures with a main service disconnecting means in each enclosure
- Panelboards with a main service disconnecting means in each panelboard enclosure
- Switchboard(s) with only one service disconnect in each separate vertical section, with barriers separating each vertical section
- Service disconnects in switchgear or metering centers where each disconnect is in a separate compartment
So a six-handle load center used as the sole service disconnect — legal for decades — is a violation on a new installation. Also note 230.71(A): disconnects that are part of listed equipment and used solely for power monitoring, surge-protective devices, the control circuit of a ground-fault protection system, or a power-operable service disconnect are not counted among the six.
The disconnects must be grouped (230.72(A)), and each must be permanently marked to identify it as a service disconnect (230.70(B)) and marked to indicate the load served. The sum of the individual disconnect ratings may exceed the ampacity of the service-entrance conductors.
Service Disconnecting Means Location (230.70)
230.70(A)(1) requires the service disconnecting means to be installed at a readily accessible location, either outside the building or structure, or inside nearest the point of entrance of the service conductors. "Readily accessible" (Article 100) means capable of being reached quickly for operation, renewal, or inspection without requiring those to whom ready access is requisite to take actions such as using tools other than keys, climbing over or under obstacles, or resorting to a portable ladder. 230.70(A)(2) prohibits installing the service disconnecting means in a bathroom — a rule that is not limited to dwellings. For one- and two-family dwelling units, an emergency disconnect (230.85) must additionally be provided in a readily accessible outdoor location with the specific marking that section requires, so fire service can de-energize the building from outside. Section 3.4 covers both rules in detail.
Service Equipment Rating (230.79)
230.79 sets the minimum rating of the service disconnecting means:
| Installation | Minimum rating | Reference |
|---|---|---|
| Limited loads of a single branch circuit | 15 A | 230.79(A) |
| Not more than two 2-wire branch circuits | 30 A | 230.79(B) |
| One-family dwellings | 100 A, 3-wire | 230.79(C) |
| All other installations | 60 A | 230.79(D) |
On a commercial project the answer is almost always the 60 A floor in 230.79(D) — but read the stem, because a small single-circuit sign or pump service can legitimately land on the 15 A or 30 A row.
Conductor Ampacity and Sizing (230.42)
230.42(A) requires service-entrance conductors to have an ampacity not less than the load served and not less than the rating of the service disconnecting means. Where the service supplies continuous loads, 230.42(A)(1) requires the conductor ampacity to be not less than 125% of the continuous load plus 100% of the non-continuous load — mirroring the feeder rule in 215.3. The continuous portion must be added at 125% because the OCPD (and conductor) carries that current indefinitely without cycling.
Service Head and Gooseneck (230.54)
Overhead service-entrance conductors are installed with drip loops and a service head (gooseneck) so water is directed away from raceway entries. 230.54(C) requires the service head to be located above the point of attachment of the overhead service conductors to the building (an exception permits it below the point of attachment, by not more than 24 in., where it is impracticable to locate it above). 230.54(F) requires drip loops on the service-entrance conductors, and 230.54(G) requires the conductors and drip loops to be arranged so that water does not enter the service raceway or equipment.
Service-Entrance Conductor Clearances
230.24(A) — Above roofs. Overhead conductors must have a vertical clearance of not less than 8 ft (2.5 m) above the roof surface, maintained for at least 3 ft in all directions from the edge of the roof, with several exceptions (for example, a reduced 3 ft clearance where the roof slope is at least 4 in. in 12 in., and an allowance where not more than 6 ft of conductor passes over not more than 4 ft of roof to reach a support).
230.24(B) — Vertical clearance to grade. This is the list the exam actually asks about, and it is driven by what is underneath the conductors, not simply by voltage:
| Clearance | Applies where |
|---|---|
| 10 ft (3.0 m) | At the electrical service entrance to buildings, at the lowest point of the drip loop, and above areas or sidewalks accessible to pedestrians only, for conductors supported on and cabled together with a grounded bare messenger where the voltage does not exceed 150 V to ground |
| 12 ft (3.7 m) | Over residential property and driveways, and over commercial areas not subject to truck traffic, where the voltage does not exceed 300 V to ground |
| 15 ft (4.5 m) | Over the same areas as the 12 ft row where the voltage exceeds 300 V to ground |
| 18 ft (5.5 m) | Over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles |
| 24.5 ft (7.5 m) | Over track rails of railroads |
Work the row from the surface below the wire first, then check whether the voltage bumps you from 12 ft to 15 ft. A 277/480 V drop crossing a truck-traffic parking lot is the 18 ft row — the voltage never gets a chance to matter, because the 18 ft row is written by land use, not by voltage.
- 230.26 — the point of attachment of overhead service conductors to a building or structure shall not be less than 10 ft (3.0 m) above finished grade, and must be located so that the minimum clearances of 230.9 and 230.24 can be maintained.
- 230.28 — where a raceway-type service mast is used, all raceway fittings must be identified for use with service masts, the mast must have adequate mechanical strength (with braces or guys where needed) to withstand the service-drop strain, and only power service-drop or overhead service conductors may be attached to the mast. Note that many jurisdictions add a local amendment naming a specific mast material such as rigid metal conduit — that is a local rule, not the NEC text.
Service Overcurrent Protection (230.90–230.95)
- 230.90 — each ungrounded service conductor shall have overcurrent protection. The OCPD shall be an integral part of the service disconnecting means or located immediately adjacent.
- 230.91 — the service OCPD shall protect the service-entrance conductors.
- 230.95 — Ground-fault protection of equipment (GFPE). GFPE is required for solidly grounded wye services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase, for each service disconnect rated 1000 amperes or more. Read the voltage condition carefully — it is more than 150 V to ground, so the rule captures 480Y/277 V services (277 V to ground) and does not capture 208Y/120 V services (120 V to ground) no matter how large they are. It also does not reach delta systems, corner-grounded systems, resistance-grounded systems, or single-phase services. The maximum GFPE setting is 1200 A, with a maximum time delay of 1 second for ground-fault currents of 3000 A or more, and 230.95(C) requires the system to be performance tested by primary current injection when first installed, with a written record available to the AHJ.
Exam trap: a 4000 A, 480Y/277 V service split into five 800 A disconnects is exempt from 230.95, because the rule is written per service disconnect, and no single disconnect reaches 1000 A.
Worked Sizing Example
A retail tenant has a calculated service load of 320 A, of which 240 A is continuous load (signage, refrigeration, and lighting operating ≥3 hours). Required service-entrance conductor ampacity per 230.42(A)(1) and 215.3:
- Continuous: 240 A × 1.25 = 300 A
- Non-continuous: 320 − 240 = 80 A
- Required ampacity = 300 + 80 = 380 A
Select a 400 A service disconnect (next standard size per 240.6(A)) and service-entrance conductors with ampacity ≥ 380 A — e.g., 500 kcmil Cu at 75 °C (≈380 A) or two parallel sets of 250 kcmil Cu. Confirm the 400 A OCPD protects the conductor per 230.90/230.91, and verify 230.95 ground-fault protection is not triggered (the service is below 1000 A).
A single service supplies a small commercial building with six circuit breakers acting as the service disconnecting means. Under the current NEC, how must those six disconnects be arranged?
A solidly grounded wye 208Y/120 V service is rated 1200 A. What does 230.95 require?
Overhead service conductors operating at 277 V to ground cross a commercial parking lot that is subject to truck traffic. What minimum vertical clearance does 230.24(B) require?