12.2 Service Disconnecting Means, Overcurrent Protection & Service Grounding

12.2 Service Disconnecting Means, Overcurrent Protection & Service Grounding

Exam Focus: 230.70 location, 230.71 six-disconnect and separate-enclosure rules, 230.72 grouping and marking, 230.90/230.91 overcurrent protection, 230.95 GFPE, and the 250.24 service grounding connections.

The service disconnecting means is the boundary of Article 230 and the point where the grounded conductor and the equipment grounding system are bonded together. Get this section right and half of Article 250 falls into place.

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Location and Accessibility — NEC 230.70

The service disconnecting means must be installed at a readily accessible location either:

• Outside the building or structure, or
• Inside nearest the point of entrance of the service conductors.

It must not be installed in a bathroom, and each disconnect must be permanently marked to identify it as a service disconnect.

[!IMPORTANT] "Nearest the point of entrance" has no number attached. The NEC does not state a permitted length of unprotected service-entrance conductor inside a building; the AHJ decides what qualifies as nearest. That is deliberate, and it is why exam items on this topic will not give you a footage figure — an option that supplies one (for example "within 10 feet") is a distractor.

The Six-Disconnect Rule — NEC 230.71

Each service must have no more than six disconnects for each service permitted by 230.2, or for each set of service-entrance conductors permitted by 230.40.

Since the 2020 NEC, where two to six service disconnecting means are used, each disconnect must be installed in a separate enclosure with a common supply. The old six-handle-in-one-panelboard arrangement is no longer permitted for new work. The 2023 NEC added an exception at 230.71(B) relieving certain existing installations with two to six disconnects from having to be upgraded.

Grouping and Marking — NEC 230.72

• The two to six disconnects must be grouped, and each must be marked to indicate the load served.
• One of the disconnects supplying fire pump, emergency, legally required standby, or optional standby service may be located remote from the others, so it is not deenergized when the normal disconnects are opened.
• Where a building has more than one service, or a combination of services and feeders, the permanent plaque or directory of 230.2(E) is required at each disconnect location.

+-------------------------------------------------------------------------+
|            SERVICE DISCONNECT REQUIREMENTS AT A GLANCE                  |
|                                                                         |
|   MAXIMUM NUMBER ....... 6 disconnects per service                      |
|   LOCATION ............. readily accessible; outside, or inside         |
|                          nearest the point of entrance; NOT a bathroom  |
|   ENCLOSURES ........... 2 to 6 disconnects = SEPARATE ENCLOSURES       |
|                          (2020 NEC change; 2023 exception for existing) |
|   GROUPING ............. grouped, each marked with the load served      |
|   MARKING .............. permanently marked as a service disconnect     |
|   MICHIGAN ADDITION .... one- and two-family dwellings also need the    |
|                          230.85 outdoor emergency disconnect marked     |
|                          "EMERGENCY DISCONNECT, SERVICE DISCONNECT"     |
+-------------------------------------------------------------------------+

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Service Overcurrent Protection — NEC 230.90 and 230.91

• 230.90(A): each ungrounded service conductor must have overload protection by an overcurrent device in series with each ungrounded conductor, rated or set not higher than the allowable ampacity of the conductor. The next-higher standard device size is permitted where the conductor ampacity does not correspond to a standard rating.
• 230.91: the service overcurrent device must be an integral part of the service disconnecting means or be located immediately adjacent to it.
• 230.95 adds ground-fault protection of equipment for large services (below).

Why the grounded conductor gets no overcurrent device: opening a neutral under load leaves the ungrounded conductors energized while unbalanced current has no return path, producing severe overvoltage on the lightly loaded leg. The NEC therefore does not permit an overcurrent device in the grounded conductor unless it simultaneously opens all conductors of the circuit (240.22).

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Ground-Fault Protection of Equipment — NEC 230.95

GFPE is required for each service disconnect rated 1,000 amperes or more on a solidly grounded wye electrical service of more than 150 volts to ground but not exceeding 1,000 volts phase-to-phase. In practice this means 480Y/277 V services of 1,000 A and up; a 208Y/120 V service is only 120 V to ground and is exempt.

Exceptions relieve continuous industrial processes where a non-orderly shutdown would introduce additional or increased hazards, and fire pumps.

[!CAUTION] GFPE is not GFCI. GFPE protects equipment from destructive arcing burndown and operates at hundreds or thousands of amperes. GFCI protects people and operates at 4 to 6 milliamperes. An item that pairs "1,200 amperes" with "protection of personnel" is wrong on its face.

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Grounding at the Service — NEC 250.24

The service is the one place in a premises wiring system where the grounded conductor and the equipment grounding system are deliberately connected.

The practical consequence is the rule already covered in Section 5.4: the neutral bus is bonded at the service and floating at every subpanel. Section 7.4 covers main and system bonding jumpers in depth.