NEC Article 230: Electrical Service Requirements Complete Guide
A comprehensive walkthrough of NEC Article 230, covering every aspect of electrical services from the utility connection to the main disconnect. Includes service drops, service laterals, overhead clearances, conductor sizing, disconnecting means, and grounding requirements.
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In This Guide
Article 230 Overview & Structure
NEC Article 230 is one of the most critical articles in the code, governing how electricity enters a building from the utility supply. Every residential, commercial, and industrial electrical installation begins with the service, making Article 230 fundamental knowledge for every electrician.
Article 230 Parts
- Part I (230.1-230.2): Scope and number of services permitted
- Part II (230.6-230.56): Overhead service-drop conductors
- Part III (230.30-230.33): Underground service-lateral conductors
- Part IV (230.40-230.56): Service-entrance conductors
- Part V (230.62-230.66): Service equipment - general
- Part VI (230.70-230.82): Service equipment - disconnecting means
- Part VII (230.90-230.95): Service equipment - overcurrent protection
- Part VIII (230.200-230.212): Services exceeding 1000 volts
Number of Services - NEC 230.2
The general rule is that a building shall be supplied by only one service. However, NEC 230.2 permits additional services when:
- Fire pumps: Separate service permitted for fire pump loads
- Emergency systems: Separate service allowed for legally required standby or emergency systems
- Multiple occupancies: Each occupancy can have its own service by special permission
- Capacity requirements: When a single service cannot supply the total load
- Different voltages/phases: When different characteristics are needed
- Large area: Buildings of large area where single service is impractical
Important: Service vs Feeder
Do not confuse "service" with "feeder." The service is the conductors and equipment from the serving utility to the service disconnecting means. Everything after the main disconnect is a feeder or branch circuit, governed by different articles. This distinction matters because service conductors have limited overcurrent protection (only at the main disconnect), while feeders have overcurrent protection at their origin.
Service Drop vs Service Lateral
There are two fundamental ways electricity reaches a building from the utility: overhead via a service drop, or underground via a service lateral. Each has distinct requirements under Article 230.
Service Drop (Overhead)
NEC 230 Part II (230.6-230.56)
- • Overhead conductors from utility pole to building
- • Typically owned and maintained by utility
- • Connects at weatherhead/service head
- • Subject to overhead clearance requirements
- • Common in residential and older commercial areas
- • Point of attachment must be adequate to support
Service Lateral (Underground)
NEC 230 Part III (230.30-230.33)
- • Underground conductors from utility to building
- • Ownership varies (utility or building owner)
- • Enters through foundation or via conduit riser
- • Subject to burial depth requirements (NEC Table 300.5)
- • Preferred for aesthetics and storm protection
- • Requires proper conduit and sealing at entry point
Service Point Definition
The service point is the point of connection between the facilities of the serving utility and the premises wiring. This is a critical demarcation - everything on the utility side is their responsibility, and everything on the building side is the owner's responsibility. The NEC applies to the building side. The utility determines the location of the service point, which is typically at the meter base or the weatherhead.
Overhead Service Clearances
NEC 230.24 specifies minimum clearances for overhead service-drop conductors. These clearances are critical safety requirements designed to prevent accidental contact with energized conductors.
Clearance Requirements - NEC 230.24
| Location | Minimum Clearance | NEC Reference |
|---|---|---|
| Above finished grade (general) | 10 feet | 230.24(B)(1) |
| Above residential driveways | 12 feet | 230.24(B)(2) |
| Above commercial driveways/parking | 18 feet | 230.24(B)(4) |
| Above public streets and roads | 18 feet | 230.24(B)(4) |
| Above rooftops (general) | 8 feet | 230.24(A) |
| Above roof (slope > 4/12, 300V max) | 3 feet | 230.24(A) Exception |
Rooftop Clearance Exceptions
The 8-foot rooftop clearance can be reduced in specific situations:
- 3 feet: Roof slope of 4 inches per 12 inches (4/12) or greater, voltage not exceeding 300V, and conductors not more than 6 feet of horizontal run over the roof
- 18 inches: Where the voltage between conductors does not exceed 300V, the roof area is guarded or not readily accessible, and has a slope of at least 4/12
- Point of attachment only: The clearance above the point of attachment is permitted to be the minimum clearance at the roof surface
Point of Attachment - NEC 230.26
The point of attachment for overhead service-drop conductors must be no less than 10 feet above finished grade. If the building structure is too short to provide adequate clearance, a service mast is used to extend the attachment point to the required height.
- Service mast must be of adequate strength per NEC 230.28
- Minimum 2-inch rigid metal conduit is typically required for service masts
- Guy wires or braces may be required per utility specifications
- Only power service-drop conductors shall be attached to a service mast per 230.28
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Service Entrance Conductors
Service entrance conductors extend from the service point (typically the weatherhead or meter base) to the service disconnecting means. NEC 230 Part IV covers their requirements.
Conductor Sizing - NEC 230.42
Service Conductor Sizing Requirements
- 230.42(A)(1): Sufficient ampacity to carry the computed load per Article 220
- 230.42(B): Minimum 100A for single-family dwellings with 6 or more 2-wire branch circuits or an initial net computed load of 10 kVA or more
- 230.79: Rating of service disconnecting means determines minimum service size
- Table 310.12: Use for conductor ampacity based on temperature rating and installation conditions
Common Service Conductor Sizes
| Service Size | Copper | Aluminum | Typical Application |
|---|---|---|---|
| 100A | #4 AWG | #2 AWG | Small homes, condos |
| 200A | 2/0 AWG | 4/0 AWG | Standard residential |
| 320A | 350 kcmil | 500 kcmil | Large homes, small commercial |
| 400A | 500 kcmil | 750 kcmil | Large residential, commercial |
SE Cable vs Individual Conductors
Service entrance conductors can be installed as SE (Service Entrance) cable or as individual conductors in conduit. SE cable types include USE (underground) and SE type (above ground). Per NEC 230.43, permitted wiring methods include rigid metal conduit, IMC, EMT (with restrictions), PVC conduit, SE cable, MC cable (listed for service entrance), and wireways.
Number of Service Entrance Conductor Sets - NEC 230.40
Each service drop or lateral shall supply only one set of service-entrance conductors, with exceptions:
- Exception 1: Two-to-six disconnects in separate enclosures at single location with plywood backing
- Exception 2: Where two to six service disconnecting means in separate enclosures are grouped at one location
- Exception 3: A single-family dwelling and a separate structure with one set of service-entrance conductors run to each
- Exception 5: Multi-occupancy buildings where each occupant has their own service equipment
Service Disconnecting Means
NEC 230 Part VI specifies the requirements for the service disconnecting means - the main disconnect that allows the entire service to be shut off. This is one of the most frequently tested areas in the NEC.
Key Requirements - NEC 230.70-230.82
- 230.70(A): Must be installed at a readily accessible location nearest the point of entrance of the service conductors
- 230.71: Maximum of six disconnects allowed (the "six-throw rule") - NOTE: NEC 2020 requires a single main disconnect for dwelling units per 230.71(B)
- 230.72: When multiple disconnects are used, they must be grouped at one location
- 230.76: Must simultaneously disconnect all ungrounded conductors
- 230.79: Minimum rating requirements based on load served
- 230.82: Equipment permitted on the supply side of the service disconnect
The Six-Throw Rule and 2020 NEC Change
Traditionally, NEC 230.71 permitted up to six switches or six circuit breakers as the service disconnect (the "six-throw rule"). This allowed installations without a main breaker, using up to six individual breakers to disconnect the entire service.
NEC 2020 Change: Emergency Disconnect for Dwellings
The 2020 NEC added Section 230.85, which requires a readily accessible outdoor emergency disconnect for one- and two-family dwelling units. This is intended for use by first responders (firefighters) to de-energize the building quickly. Key requirements:
- Must be installed in a readily accessible outdoor location
- Must be marked as "Emergency Disconnect"
- Must disconnect all ungrounded conductors of the service
- Can be the meter main disconnect, a separate disconnect, or listed as an emergency disconnect
Disconnect Location Requirements
- Readily accessible: Capable of being reached quickly without climbing over obstacles, using ladders, or removing obstructions
- Nearest point of entrance: Located as close as practical to where service conductors enter the building
- Inside or outside: Can be located inside or outside per the NEC, but many jurisdictions require outdoor disconnects
- Not in bathrooms: Service equipment is not permitted in bathrooms per 230.70(A)(2)
Service Grounding Requirements
Proper grounding and bonding at the service is covered by both Article 230 and Article 250. The service is the single point where the grounded conductor (neutral) is bonded to the grounding electrode system.
Service Grounding Requirements Summary
- Main bonding jumper: Required to connect the grounded (neutral) conductor to the equipment grounding conductor and the enclosure at the service (NEC 250.24(B))
- Grounding electrode conductor (GEC): Connects the service neutral/ground to the grounding electrode system (NEC 250.24(D))
- Grounding electrode system: Per NEC 250.50, must include all available electrodes (water pipe, building steel, ground rods, concrete-encased electrode)
- Bonding: All metallic parts of the service (conduit, enclosures, meter base) must be effectively bonded per NEC 250.92
Grounding Electrode System - NEC 250.50
All available grounding electrodes at each building or structure must be bonded together to form the grounding electrode system:
| Electrode Type | NEC Section | Requirements |
|---|---|---|
| Metal water pipe | 250.52(A)(1) | 10 ft or more in contact with earth, supplemented |
| Metal building frame | 250.52(A)(2) | Effectively grounded (10 ft of steel in earth or bonded) |
| Concrete-encased (Ufer) | 250.52(A)(3) | 20 ft of rebar or 20 ft of #4 AWG bare copper in foundation |
| Ground ring | 250.52(A)(4) | #2 AWG bare copper encircling building at 2.5 ft depth |
| Ground rods/pipes | 250.52(A)(5) | 8 ft rod, 5/8" dia (copper-clad). Two rods if resistance >25 ohms |
Two Ground Rods Required?
Per NEC 250.53(A)(2), a single ground rod that does not have a resistance of 25 ohms or less must be supplemented by an additional electrode. In practice, most electricians install two ground rods at least 6 feet apart (NEC 250.53(A)(3)) rather than performing the resistance test. This has become standard practice for residential services.
Common Article 230 Violations
Article 230 violations are among the most commonly cited issues during electrical inspections. Being aware of these common problems helps you avoid costly callbacks and failed inspections.
Frequently Cited Violations
- Inadequate overhead clearances: Service drop not meeting minimum heights over driveways, sidewalks, or rooftops. The most common issue is 12-foot clearance over residential driveways not met.
- Missing main bonding jumper: The green bonding screw or strap in the main panel not installed, leaving the neutral and ground bus unbonded at the service.
- Undersized service conductors: Service conductors that do not meet the computed load requirements per Article 220. Often occurs during service upgrades when the load has increased.
- Disconnect not readily accessible: Main disconnect blocked by storage, equipment, or installed above 6 feet 7 inches to the handle in the highest position.
- Improper grounding electrode system: Missing supplemental ground rod, improperly bonded water pipe, or missing concrete-encased electrode when available.
- More than six disconnects: Exceeding the six-throw rule or, for 2020 NEC jurisdictions, lacking a single emergency disconnect for dwelling units.
- Service mast inadequate: Service mast not properly sized or supported to handle the weight and wind loading of the service-drop conductors.
Pre-Inspection Checklist
- ✓Overhead clearances meet NEC 230.24 minimums
- ✓Weatherhead/service head properly installed above point of attachment
- ✓Service entrance conductors properly sized per load calculation
- ✓Service mast adequately supported and sized
- ✓Main disconnect readily accessible and properly rated
- ✓Main bonding jumper installed
- ✓Grounding electrode system complete and properly bonded
- ✓Two ground rods installed (or 25-ohm test documented)
- ✓Water pipe bond installed (if metallic water piping present)
- ✓Surge protective device installed (NEC 2020 dwelling units)
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