What Article 230 Covers
NEC Article 230 is the primary code section governing the installation of service conductors — the conductors that bring power from the utility's distribution system into a building or structure. It covers everything from where the conductors attach to the building, how high overhead conductors must be above various surfaces, how the conductors enter the building, the required size of the service disconnect, and ground fault protection for large services.
Article 230 applies to all buildings served by a utility — from a small residential dwelling to a large industrial facility. Understanding its requirements is essential for designing, installing, and inspecting service entrance equipment.
Service Drop vs. Service Lateral
The NEC distinguishes between two types of utility service based on how the conductors run from the utility distribution system:
- Service Drop (Overhead): Overhead conductors that run from the utility pole to the building's point of attachment. The utility typically owns the service drop up to the attachment point, but the homeowner or building owner is responsible for the service entrance conductors below the attachment point and the service entrance equipment.
- Service Lateral (Underground): Underground conductors that run from the utility's transformer or underground distribution system to the building. Underground services are increasingly common in new subdivisions. The utility typically owns the service lateral up to the meter base.
NEC 230 contains provisions for both, but the clearance requirements in 230.9 and 230.24 apply specifically to overhead (service drop) installations.
NEC 230.9 — Clearances from Building Openings
Service conductors (overhead) must maintain specific clearances from building openings to prevent contact by persons using doors, windows, or similar openings. Per NEC 230.9:
- Service conductors must have a minimum clearance of 3 feet from windows that are designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations
- Exception: Conductors that run above the top of a window are exempt from the 3-foot rule — they can pass directly above the window opening
This requirement is a common source of inspection failures in older neighborhoods where utility poles are close to buildings and the service drop approaches windows from the side rather than from above.
NEC 230.24 — Overhead Conductor Clearances Above Ground
Overhead service conductors must maintain minimum heights above various surfaces to protect against accidental contact from pedestrians, vehicles, and ladders. The NEC establishes tiered clearances based on the type of surface below:
| Surface Type | Minimum Clearance | NEC Reference |
|---|---|---|
| Final grade or sidewalk accessible to pedestrians only | 10 feet | 230.24(B)(1) |
| Residential driveways and commercial areas not subject to truck traffic | 12 feet | 230.24(B)(2) |
| Public streets, alleys, roads, and driveways subject to truck traffic | 18 feet | 230.24(B)(3) |
| Agricultural or other areas subject to trucks and farm equipment | 18 feet | 230.24(B)(4) |
These clearances are measured from the lowest point of the conductor at maximum sag (considering temperature and loading conditions). The inspector will visually verify that the service drop appears to maintain these clearances — if the conductors appear to sag below these heights, a formal measurement may be required.
NEC 230.26 — Point of Attachment
The point of attachment is where the service drop connects to the building — typically at the weatherhead (service head) on a service mast or a porcelain knob insulator on the building wall. Per NEC 230.26:
- The point of attachment must be no less than 10 feet above finished grade
- If the 10-foot minimum cannot be met, the attachment must be high enough to satisfy the 230.24 clearances at the lowest point of the service drop span
- The utility will specify an exact height based on the pole location and span length — design engineers should coordinate with the serving utility early in the project
NEC 230.28 — Service Masts
A service mast is a conduit or pipe that extends above the roof to provide the required clearances for the service drop. NEC 230.28 requires that service masts used as the point of attachment:
- Must be of adequate strength to support the service drop — the utility may specify minimum pipe sizes (typically 2-inch rigid metal conduit for residential services)
- Must be supported adequately at the roof and building — roof flashing and wall brackets must be watertight and structurally sound
- The weatherhead (service head) at the top must be positioned so that service conductors enter from above, with the service head pointing away from the building, to prevent water entry
- Roof clearance: where service conductors pass above a roof with a slope of less than 4 inches per foot (4:12 pitch), a minimum 8-foot clearance is required; for steeper slopes, a reduced clearance of 3 feet is permitted per the exceptions in 230.24(A)
NEC 230.42 — Service Entrance Conductor Sizing
Service entrance conductors must be sized to carry the load calculated in accordance with Article 220 (load calculations). In addition:
- The conductors must have an ampacity of at least 100% of the calculated load (no demand factor reduction applies to the service entrance conductors themselves)
- The conductors must not be smaller than required to serve the service disconnect rating
- For a 200A residential service, the service entrance conductors are typically 2/0 AWG aluminum or 1/0 AWG copper for each ungrounded conductor
- The service neutral conductor is sized based on the calculated neutral load, but must not be smaller than the grounding electrode conductor size required by Table 250.66
NEC 230.70 — Service Disconnect Requirements
The service disconnect is the means by which the entire electrical system of a building can be de-energized. This is one of the most critical safety features at any service entrance.
Location Requirements
- The service disconnect must be installed at a readily accessible location either inside or outside a building or structure — and it must be nearest the point of entrance of the service conductors per NEC 230.70(A)(1)
- The service disconnect must not be installed in bathrooms per NEC 230.70(A)(2)
- For multiple-occupancy buildings, the service disconnect for each occupancy must be accessible to the occupant it serves
Marking Requirements
Per NEC 230.70(B), the service disconnect must be permanently marked to identify it as a service disconnecting means. In a load center, this is typically satisfied by the "MAIN" label on the main breaker. In a meter-main combination unit, the marking is usually on the main breaker or fused disconnect.
NEC 230.71 — The Six-Handle Rule
NEC 230.71 limits the number of service disconnects for a building to a maximum of six. This means that when a building is served by a single service, all of that building's electrical service can be disconnected by operating no more than six individual disconnecting means. In practice, most modern residential services use a single main breaker (one handle), while some commercial services use a meter-main with multiple main disconnects limited to six.
NEC 230.79 — Service Disconnect Rating
The service disconnect must be rated for the calculated load, with minimum ratings specified by occupancy type:
- One-circuit installations: Minimum 15A
- Two-circuit installations: Minimum 30A
- Single-family dwelling: Minimum 100A, three-wire, per 230.79(C)
- All other installations: As calculated per Article 220, minimum 60A per 230.79(D)
NEC 230.82 — Equipment Connected to Supply Side of Service Disconnect
Normally, only specific types of equipment may be connected on the supply (utility) side of the service disconnect — that is, in the "always energized" portion of the service. Per NEC 230.82, permitted supply-side connections include:
- Cable limiters or current-limiting devices
- Meters and meter sockets rated for the application
- Surge protective devices (SPDs) listed for supply-side connection
- Conductors to a remote service disconnect
- Connections to load-side conductors from multiple utility connections
- Solar PV and energy storage system interconnections (under specific conditions per NEC 690 and 706)
NEC 230.95 — Ground Fault Protection of Equipment
For services of 1000A or higher at 150V to ground and above (common at 480Y/277V systems), NEC 230.95 requires ground fault protection of equipment (GFPE) at the service disconnect. Key requirements:
- GFPE is required to operate at a maximum setting of 1200A
- A test must be performed after installation to verify operation — a written record of the test must be made and retained on or at the premises per 230.95(C)
- Solidly grounded systems of 1000A or greater require GFPE unless an alternative ground fault protection arrangement is provided downstream
- The NEC does not require GFPE on ungrounded systems or on systems operating at less than 150V to ground (not applicable to 208Y/120V systems in most configurations)
GFPE trips for ground faults in the range of 100-1200A — faults too large for GFCI (which trips at 5mA for personnel protection) but below the level that would cause the main overcurrent device to operate quickly, making GFPE essential for equipment protection in large services.
Common Article 230 Violations
| Violation | NEC Section |
|---|---|
| Service conductors within 3 feet of opening window | 230.9 |
| Service drop below 10 feet over sidewalk | 230.24(B)(1) |
| Service drop below 12 feet over residential driveway | 230.24(B)(2) |
| Point of attachment below 10 feet above grade | 230.26 |
| Service disconnect not labeled as service disconnect | 230.70(B) |
| Service disconnect installed in a bathroom | 230.70(A)(2) |
| More than six service disconnects | 230.71 |
| Missing GFPE on 1000A+ 480V service | 230.95 |
| Service entrance conductors undersized for calculated load | 230.42 |
| No watertight seal at service entrance conduit | 230.54 |