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NEC Requirements for Services — Part 2

May 15, 2024
Do you know the rules for service entrance conductors and service disconnects?

Service-entrance conductors differ from service conductors. They are the conductors between the terminals of the service equipment and the service drop, overhead service conductors, service lateral, or underground service conductors [Art. 100]. By contrast, service conductors run from the service point to the service disconnect [Art. 100].

Each service drop, service lateral, or set of underground or overhead service conductors can supply only one set of service-entrance conductors [Sec. 230.40]. There are five exceptions. For example, Exception No. 2: Service-entrance conductors can supply two to six service disconnects per Sec. 230.71(B).

Service conductors must have an ampacity of at least the largest of the calculations in Sec. 230.42(A)(1) or (2) [Sec. 230.42]. For example, service conductors must have an ampacity of at least 125% of the continuous loads, plus 100% of the noncontinuous loads, based on the temperature rating of equipment per Sec. 110.14(C)(1) and Table 310.16, before conductor ampacity correction and/or adjustment [Sec. 230.42(A)(1)].

The service neutral conductor must have an ampacity to carry the maximum unbalanced load per Sec. 220.61 and not be smaller than required by Sec. 250.24(D) [Sec. 230.42(C)].

Service-entrance conductors can be installed with any of the 21 wiring methods listed in Sec. 230.43 —for example, wireways, EMT, and MC cable.

Pressure connectors, devices for splices and tap connections, and power distribution blocks installed on service conductors must be listed and marked “suitable for use on the line side of the service equipment” or equivalent [Sec. 230.46], as shown in Fig. 1.

You must protect service-entrance cables subject to physical damage using one of the six methods listed in Sec. 230.50(B)(1) through (6). For example, use EMT.

Service-entrance cable must be supported within 1 ft of the weatherhead, gooseneck, raceway connections, or enclosure. Supports must be at intervals not exceeding 30 in. [Sec. 230.51(A)].
Service weatherheads on raceways or service-entrance cables must be above the point of attachment [Sec. 230.26] for service-drop or overhead service conductors [Sec. 230.51(C)].

Exception: If it is impractical to locate the service head above the point of attachment, it must be within 2 ft of the point of attachment.

Drip loop conductors must be connected to the service-drop or overhead service conductors below the service head or termination of the service-entrance cable sheath [Sec. 230.51(F)].

On a 4-wire, delta-connected, 3-phase high-leg system, the conductor with the higher phase voltage-to-ground (208V high-leg) must be durably and permanently marked by an orange outer finish or other effective means [Sec. 230.56]. Such identification must be placed at each point on the system where both a connection is made and the neutral conductor is present [Sec. 110.15].

Surge protection

Where a service supplies any of the following occupancies, you must provide a surge-protective device [Sec. 230.67(A)]:

(1) Dwelling units (Fig. 2).

(2) Dormitory units.

(3) Guest rooms and guest suites of hotels and motels.

(4) Areas of nursing homes and limited care facilities used exclusively as patient sleeping rooms.

The surge-protective device must be a Type 1 or Type 2 SPD [Sec. 230.67(C)] and must be an integral part of the service disconnect or be immediately adjacent to the service disconnect [Sec. 230.67(B)]. Exception: The surge-protective device is permitted to be at the downstream panelboard.

Service disconnect

The service disconnect must be marked to identify it as suitable for use as service equipment and must be permanently marked to identify it as a service disconnect [Sec. 230.66(A)].
The service disconnect must open all phase conductors [Sec. 230.70]. It must be placed at a readily accessible location either outside the building or inside nearest the point of service conductor entry [Sec. 230.70(A)(1)].

Each service must have only one service disconnect except as permitted in Sec. 230.71(B). Each service can have up to six service disconnects per Sec. 230.71(B)(1) through (5) — for example, panelboards with a service disconnect in each panelboard.

The service disconnects for each service must be grouped and marked to indicate the load served [Sec. 230.72(A)].

To minimize the possibility of simultaneous interruption of power, the disconnect for fire pumps [Art. 695], emergency systems [Art. 700], legally required standby systems [Art. 701], or optional standby systems [Art. 702] must be remote from the service disconnect(s) for normal service [Sec. 230.72(B)].

The service disconnect for a building must have an ampere rating of at least the calculated load per Art. 220, and in no case can it be less than the values listed in Sec. 230.79(A) through (D). For example, for installations consisting of two 2-wire branch circuits, the disconnect must have an ampere rating of at least 30A.

Only 11 types of electrical equipment can be connected to the supply side of the service disconnect [Sec. 230.82]. For example:

  • Cable limiters.
  • Meters and meter sockets rated at least 1,000V.
  • Type 1 SPDs.
  • Emergency disconnects for one- and two-family dwelling units.

Emergency disconnect

For one- and two-family dwelling units, an emergency disconnect must be installed per Sec. 230.85(A) through (E).

(A) General. The requirements are about what you’d expect: readily accessible, within sight from the dwelling unit, has a short-circuit rating of at least that of the available fault current, and grouped if more than one disconnect (Fig. 3).

(B) Type. It has to be a service disconnect, integrated meter disconnect, or other listed switch or circuit breaker suitable for service equipment.

(C) Replacement. Where a service disconnect is replaced, all the requirements of this section apply.

(D) Identification. Where disconnects for other energy source systems are not adjacent to the emergency disconnect, a plaque or directory identifying the location of all other energy source disconnects must be adjacent to the emergency disconnect.

(E) Marking. There are five marking requirements. For example, the markings or labels must be on the outside front of the disconnect with a red background and white text.

Service conductor overcurrent protection

Each service phase conductor must have overload protection [Sec. 230.90].
The service overcurrent protective device provides overload protection for the line side of service conductors, but not short-circuit and ground-fault protection because that protection can be provided only at the supply end of a circuit.

The rating of the overcurrent protective device must not be greater than the ampacity of the service phase conductors [Sec. 230.90(A)].

Exception No. 2: If the ampacity of the phase conductors does not correspond with the standard rating of overcurrent protective devices as listed in Sec. 240.6(A), the next higher overcurrent protective device can be used if it does not exceed 800A [Sec. 240.4(B)].

Exception No. 3: The combined ratings of two to six service disconnects can exceed the ampacity of the service conductors only if the calculated load does not exceed the ampacity of the service conductors per Art. 220.

Exception No. 5: Overload protection for dwelling unit services is permitted per the requirements of Sec. 310.12.

The service disconnect fuse or circuit breaker supplies overload protection — but not short-circuit and ground-fault protection — for the line-side service conductors.

The service grounded conductor can terminate on a circuit breaker that simultaneously opens all conductors of the circuit [Sec. 230.90(B)]. A breaker so configured is the only overcurrent device that can be inserted into a grounded service conductor.

The service overcurrent protective device must be an integral part of the service disconnect or be immediately adjacent to the service disconnect [Sec. 230.91]. Where fuses are used as the service overcurrent protective device, the disconnect must be ahead of the supply side of the fuses.

Each service disconnect rated 1,000A or more supplied by a 4-wire, 3-phase, 277V/480V wye-connected system must be provided with ground-fault protection of equipment [Sec. 230.95]. The rating of the service disconnect is based on the rating of the largest fuse that can be installed or the circuit breaker’s highest continuous current trip setting.

Code compliant services

Article 230 is one of the larger Articles in the Code. It’s also complex, with many rules that can be hard to check at the drawing desk or in the field. This fact has not gone unnoticed by Code-Making Panel Number 10 (the CMP responsible for Art. 230). For many Code cycles now, Figure 230.1 has provided both a list and a graphic that show you how Art. 230 is laid out.

You can see at a glance that if you’re working with overhead conductors, you need to refer to Part II. However, if those conductors are underground you need to refer to Part III. So look at this table to identify which Part of Art. 230 matches where you are in your design workflow or installation process.

Don’t confuse service conductors (Parts II and III) with service-entrance conductors, either.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

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