NEC Article 230 — Services: Everything the Exam Tests

Article 230 covers the electrical service — the point where utility power enters a building and becomes the building owner's responsibility. Understanding Article 230 is critical not just for the exam, but for real-world electrical work: improper services are a leading cause of inspection failures and code violations.

The exam tests specific numbers from this article: clearance distances, conductor sizes, the six-disconnect rule, and service disconnect location requirements. Know these cold and you'll handle most Article 230 questions without looking anything up.

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Scope: Where Article 230 Applies

Article 230 covers conductors and equipment from the service point to the service disconnecting means. The service point is where the utility conductors connect to the premises wiring — typically at the weatherhead, meter socket, or transformer pad.

What Article 230 does NOT cover:

• Utility-owned conductors (those belong to the electric company)
• Conductors downstream of the service disconnecting means (those are feeders, covered by Article 225)

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Number of Services: 230.2

The general rule is simple: one service per building or structure.

But the exceptions are exam-tested:

230.2 Exceptions (a building may have additional services for):

• Fire pumps
• Emergency systems
• Legally required standby systems
• Optional standby systems
• Parallel power production systems
• Buildings with two or more occupancies
• Capacity requirements exceeding a single service
• Buildings of large area (documented necessity)

Exam tip: Questions typically ask something like "A 10-story office building has four separate services. Which NEC section permits this?" The answer is 230.2 — specifically the large capacity or multiple-occupancy exception.

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Overhead Service Conductors: Clearances

Vertical Clearance Above Ground: 230.24(B)

Overhead service conductors must maintain the following minimum clearances above ground:

Exam tip: These clearances appear frequently on exams. The 18-foot requirement for roads and the 10-foot requirement for pedestrian-only areas are the most commonly tested.

Clearance Over Roofs: 230.24(A)

The general rule is 8 feet above the roof surface. But there are important exceptions:

• 3 feet — where the roof has a slope of 4 inches in 12 inches or greater AND the conductors pass over no more than 4 feet of the roof
• 18 inches — where conductors pass over the overhang (eave) portion of a dwelling and terminate in a through-the-roof raceway or approved support

Horizontal Clearance from Buildings: 230.9

Overhead service conductors must maintain at least 3 feet from windows designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, and similar locations.

Exception: Conductors running above the top of a window are permitted with no minimum horizontal clearance.

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Service Entrance Conductors

Sizing Service Entrance Conductors

Service entrance conductors must be sized to carry the calculated load. The minimum size for a service to a single-family dwelling is specified in NEC 230.42(B): conductors must have an ampacity not less than the load calculated per Article 220 or not less than 100 amps.

100 amps is the minimum service size for a single-family dwelling. (This is frequently exam-tested.)

Number of Sets of Service Entrance Conductors: 230.40

As a general rule, each service drop or lateral must supply only one set of service entrance conductors. However, exceptions permit multiple sets where the building qualifies for more than one service under 230.2, or where the service supplies a multiple-occupancy building with individual services.

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Service Disconnecting Means: 230.70–230.82

This is one of the most heavily tested parts of Article 230.

Location of Service Disconnect: 230.70(A)

The service disconnecting means must be:

• Readily accessible
• Located either outside a building or nearest the point of entrance of the service conductors

The intent is that the disconnect must be findable and operable by emergency responders without having to enter unsafe areas of the building.

Marking: 230.70(B)

The service disconnecting means must be permanently marked to identify it as a service disconnect.

Maximum Number of Disconnects: 230.71(A)

Maximum 6 disconnects are permitted to serve as the service disconnecting means, all grouped at one location (or in two or three locations for multiple-occupancy buildings).

This is the famous "6 disconnect rule" — and it's on virtually every exam. Note:

• A single main breaker = 1 disconnect (all branch breakers downstream don't count)
• A loadcenter with 6 individual 2-pole breakers and no main = 6 disconnects (the maximum without a main)
• 7 or more individually operated disconnects is a code violation without a single main disconnect

Disconnect Rating: 230.79

The service disconnecting means must have a rating of:

• Not less than the load calculated per Article 220
• Minimum 100 amps for one-family dwellings (230.79(C))
• Minimum 60 amps for other occupancies not exceeding 6 two-wire circuits or with loads not exceeding that of 6 two-wire circuits (230.79(A))

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Service Overcurrent Protection: 230.90

Each ungrounded service entrance conductor must be protected by an overcurrent device. The device must be in series with each ungrounded service entrance conductor and have a rating not higher than the ampacity of the conductor.

Important: Service entrance conductors between the service point and the service disconnecting means are NOT protected against overcurrent by the disconnect. The overcurrent protection is at the service disconnect itself (the main breaker). This is why service entrance conductors running from the weatherhead to the panel must be sized properly — there's nothing protecting them from overcurrent except proper installation.

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Underground Service: 230.30–230.32

Underground service lateral conductors must be installed per applicable conduit fill and wiring method rules. Key requirements:

• Service laterals must be insulated where they are part of the premises wiring
• Conduit or raceway is required where conductors emerge from the ground (230.32)
• Minimum burial depths follow Table 300.5 (not Article 230 itself, but referenced)

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Service Mast and Weatherhead

Where the service enters through the roof, a service mast (a rigid conduit installation through and above the roof) is used to support the service conductors and maintain clearances. The weatherhead at the top of the mast provides a drip loop to prevent water entry. Article 230 requires that service raceways and service masts be structurally adequate and properly supported.

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Key Article 230 Numbers to Remember

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Ready to Test Your Article 230 Knowledge?

Article 230 clearance and disconnect questions are on nearly every exam. GetLicenseReady's practice questions include specific Article 230 scenarios covering service clearances, disconnect rules, and service sizing.

Related reading: NEC Article 220 — Load Calculations | NEC Article 250 — Grounding and Bonding | How to Pass the Electrician Exam on Your First Try