8.1 Service Conductors, Clearances and Service Equipment
Key Takeaways
- NEC 230.24(B) requires overhead service conductor clearances of 10 feet above pedestrian-only areas at not over 150 volts to ground, 12 feet over residential property and driveways at not over 300 volts to ground, 15 feet where the voltage exceeds 300 volts to ground, and 18 feet over public streets and truck-traffic areas.
- NEC 230.24(A) requires 8 feet of clearance above roofs, with Exception No. 3 permitting a reduction to 18 inches above only the overhanging portion where not more than 6 feet of conductor passes above the roof, not more than 4 feet horizontally, terminating at a through-the-roof raceway or approved support.
- NEC 230.9 requires service conductors to maintain 3 feet of clearance from windows designed to be opened, doors, porches, balconies, ladders, stairs, and fire escapes, except above the top level of a window.
- NEC 230.2 permits only one service to a building or structure, with listed exceptions for special conditions, special occupancies, capacity requirements, different characteristics, and documented switching procedures.
- NEC 230.70(A)(1) requires the service disconnecting means to be installed at a readily accessible location either outside the building or inside nearest the point of entrance of the service conductors.
Where the Code Starts
90.2(B)(5) excludes installations under the exclusive control of an electric utility from the NEC. Article 100 defines the service point as the point of connection between the facilities of the serving utility and the premises wiring. Everything from that point onward is yours; everything before it belongs to the utility and to the National Electrical Safety Code.
The defined terms matter and are frequently tested:
| Term | Meaning |
|---|---|
| Service conductors | The conductors from the service point to the service disconnecting means |
| Service drop | The overhead conductors between the utility electric supply system and the service point |
| Overhead service conductors | The overhead conductors between the service point and the first point of connection to the service-entrance conductors |
| Service lateral | The underground conductors between the utility electric supply system and the service point |
| Underground service conductors | The underground conductors between the service point and the first point of connection to the service-entrance conductors |
| Service-entrance conductors | The service conductors between the terminals of the service equipment and a point outside the building, or the point of connection to the service drop, overhead service conductors, service lateral, or underground service conductors |
| Service equipment | The necessary equipment, usually one or more circuit breakers or switches and fuses, connected to the load end of service conductors, intended to constitute the main control and cutoff of the supply |
Number of Services — 230.2
A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D).
- (A) Special Conditions. Fire pumps; emergency systems; legally required standby; optional standby; parallel power production systems; systems designed for connection to multiple sources for enhanced reliability.
- (B) Special Occupancies. By special permission, multiple-occupancy buildings where there is no available space for service equipment accessible to all occupants, or a single building or structure sufficiently large to make two or more services necessary.
- (C) Capacity Requirements. Where capacity requirements are in excess of 2000 amperes at a supply voltage of 1000 volts or less; where the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service; or by special permission.
- (D) Different Characteristics. Different voltages, frequencies, or phases, or for different uses such as different rate schedules.
230.2(E) Identification. Where a building or structure is supplied by more than one service, or any combination of branch circuits, feeders, and services, a permanent plaque or directory shall be installed at each service disconnect location denoting all other services, feeders, and branch circuits supplying that building and the area served by each.
Overhead Service Clearances — 230.24
230.24(A) Above Roofs. Conductors shall have a vertical clearance of not less than 8 feet (2.5 m) above the roof surface, maintained for a distance of not less than 3 feet in all directions from the edge of the roof.
| Exception | Condition | Reduced clearance |
|---|---|---|
| No. 1 | Area above the roof is subject to pedestrian or vehicular traffic | Use the 230.24(B) clearances instead |
| No. 2 | Voltage between conductors does not exceed 300, and the roof slope is not less than 4 in. in 12 in. | 3 ft |
| No. 3 | Voltage between conductors does not exceed 300, and not more than 6 ft of conductor, 4 ft horizontally, passes above the roof overhang, terminating at a through-the-roof raceway or approved support | 18 in. above only the overhanging portion |
| No. 4 | The requirement for maintaining the clearance 3 ft in all directions from the edge of the roof does not apply to the final conductor span where the conductors are attached to the side of a building | — |
Exceptions 2 and 3 are constantly swapped. Exception No. 2 is the sloped-roof rule at 3 feet. Exception No. 3 is the roof-overhang service-mast rule at 18 inches.
230.24(B) Vertical Clearance for Overhead Service Conductors. Overhead service conductors shall have the following minimum clearance from final grade:
| Clearance | Condition |
|---|---|
| 10 ft | At the electric service entrance to buildings, at the lowest point of the drip loop, and above areas or sidewalks accessible only to pedestrians, measured from final grade or other accessible surface, only for service-drop cables supported on and cabled together with a grounded bare messenger where the voltage does not exceed 150 volts to ground |
| 12 ft | Over residential property and driveways, and those commercial areas not subject to truck traffic, where the voltage does not exceed 300 volts to ground |
| 15 ft | For those areas listed in the 12-foot classification where the voltage exceeds 300 volts to ground |
| 18 ft | Over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles, such as cultivated, grazing, forest, and orchard |
| 24.5 ft | Over the track rails of railroads |
Note the deliberate trap in the 12-foot row: a residential driveway is 12 feet even where the homeowner parks a pickup, because the 18-foot row applies to "driveways on other than residential property."
230.9 Clearances on Buildings. Service conductors installed as open conductors or multiconductor cable without an overall outer jacket shall have a clearance of not less than 3 feet (900 mm) from windows that are designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations. Exception: conductors run above the top level of a window shall be permitted to be less than 3 feet.
230.9(C) Above Final Grade. Service conductors shall have a clearance of not less than 10 feet (3.0 m) above the final grade or lower level, where not readily accessible.
Service Masts — 230.28
230.28(A) Strength. Where a service mast is used for the support of overhead service conductors, it shall be of adequate strength or be supported by braces or guys to withstand safely the strain imposed by the service-drop or overhead service conductors. Hubs intended for use with a conduit that serves as a service mast shall be identified for use with service-entrance equipment.
230.28(B) Attachment. Only power service-drop or overhead service conductors shall be permitted to be attached to a service mast. Communications, CATV, and other cables may not be strapped to it.
Wiring Methods and Support — Parts IV and V
230.43 Wiring Methods for 1000 Volts, Nominal, or Less. Service-entrance conductors shall be installed in accordance with the applicable requirements of the Code covering the type of wiring method used and shall be limited to the listed methods: open wiring on insulators; Type IGS cable; rigid metal conduit; intermediate metal conduit; electrical metallic tubing; electrical nonmetallic tubing; service-entrance cables; wireways; busways; auxiliary gutters; rigid polyvinyl chloride conduit; cablebus; Type MC cable; mineral-insulated cable; flexible metal conduit or liquidtight flexible metal conduit not over 6 feet long between raceways or between raceway and service equipment with a wire-type equipment bonding jumper; liquidtight flexible nonmetallic conduit; high density polyethylene conduit; nonmetallic underground conduit with conductors; and reinforced thermosetting resin conduit.
230.50 Protection Against Physical Damage. Underground service-entrance conductors shall be protected against physical damage in accordance with 300.5. All other service-entrance conductors shall be protected where subject to physical damage.
230.51(A) Service-Entrance Cables. Service-entrance cable shall be supported by straps or other approved means within 12 inches (300 mm) of every service head, gooseneck, or connection to a raceway or enclosure and at intervals not exceeding 30 inches (750 mm).
230.54 Overhead Service Locations.
- (A) Service raceways shall be equipped with a rain-tight service head at the point of connection to service-drop or overhead service conductors.
- (B) Service-entrance cables shall be equipped with a rain-tight service head, or the cable shall be formed in a gooseneck and taped with self-sealing weather-resistant thermoplastic.
- (C) Service heads and goosenecks in service-entrance cables shall be located above the point of attachment of the service-drop or overhead service conductors to the building. Exception: where it is impracticable, the service head or gooseneck shall be permitted to be located not further than 24 inches (600 mm) from the point of attachment.
- (F) Drip loops shall be formed on individual conductors. To prevent the entrance of moisture, service-entrance conductors shall be connected to the service-drop or overhead service conductors below the level of the service head and below the termination of the service entrance cable sheath.
- (G) Service-drop conductors and service-entrance conductors shall be arranged so that water will not enter service raceway or equipment.
230.53 Raceways to Drain. Where exposed to the weather, raceways enclosing service-entrance conductors shall be raintight and arranged to drain.
Underground Service Conductors — Part III
230.30(A) requires underground service conductors to be insulated for the applied voltage, with limited exceptions for bare copper used in a raceway or for direct burial where suitable for the soil conditions, bare copper for direct burial where bare copper is judged suitable by the authority having jurisdiction, and bare copper or aluminum in cable assemblies identified for underground use.
230.32 Protection Against Damage. Underground service conductors shall be protected against damage in accordance with 300.5. Service conductors entering a building shall be installed in accordance with 230.6 or protected by a raceway wiring method identified in 230.43.
230.6 Conductors Considered Outside the Building. Conductors are considered outside a building or other structure where they are:
- Installed under not less than 2 inches (50 mm) of concrete beneath a building;
- Installed within a building in a raceway that is encased in concrete or brick not less than 2 inches thick;
- Installed in a vault that meets the construction requirements of Article 450, Part III;
- Installed in conduit and under not less than 18 inches (450 mm) of earth beneath a building;
- Installed in overhead service masts on the outside surface of the building traveling directly to the point of penetration.
This is why service conductors may run some distance "inside" a building before reaching the disconnect — encased in concrete, they are legally outside.
Service Conductor Sizing
230.42(A) requires ungrounded service-entrance conductors to have an ampacity not less than either the sum of the noncontinuous loads plus 125 percent of the continuous load, or the sum of continuous and noncontinuous loads where the assembly including overcurrent devices is listed for operation at 100 percent of its rating.
230.42(B) Specific Installations. In addition, the service-entrance conductors shall have adequate ampacity to carry the current as computed in accordance with Part III, IV, or V of Article 220.
230.42(C) Grounded Conductors. The grounded conductor shall not be smaller than the minimum size required by 250.24(C).
230.79 Rating of Service Disconnecting Means. The service disconnecting means shall have a rating not less than the calculated load:
| Installation | Minimum rating |
|---|---|
| (A) One-circuit installation | 15 A |
| (B) Two-circuit installations | 30 A |
| (C) One-family dwelling | 100 A, 3-wire |
| (D) All others | 60 A |
Remember 310.12(A) from Chapter 4 of this guide: a one-family dwelling service on a single-phase 120/240 V system rated 100 A through 400 A may have conductors sized at 83 percent of the service rating. The disconnect must still be rated at least 100 A.
Overhead service conductors at 240 volts pass over a residential driveway. What is the minimum clearance above final grade under NEC 230.24(B)?
A service mast passes through a roof overhang. Not more than 6 feet of service-drop conductor, 4 feet horizontally, passes above the overhang, and the voltage between conductors is 240 volts. What is the minimum clearance above the overhang, and which exception applies?
What is the minimum rating of the service disconnecting means for a one-family dwelling under NEC 230.79(C)?
Under NEC 230.6, which arrangement makes conductors run through a building legally 'outside the building'?