Article 230, which consists of seven parts, provides the installation requirements for service conductors and equipment. Parts II, III, and IV address conductors. For now, we'll focus on the requirements for equipment, which are covered in Parts I, V, VI, and VII. The titles of these are General, Service Equipment, Disconnecting Means, and Overcurrent Protection, respectively.
Article 100 tells us that service equipment:
Constitutes the main control and cutoff of the electricity supply.
Usually consists of circuit breakers (or switches and fuses) and their accessories.
Connects to the load end of service conductors in a structure.
Service equipment doesn't include the metering equipment, such as the meter and meter enclosure [230.66].
The service conductors, which supply power to the service equipment, originate at the service point. Service conductors terminate on the line side of the service disconnecting means. That is, they run from the service point to your service equipment.
The feeder conductors for the premises typically are connected to the load side of the service disconnect(s), but don't confuse them as part of the service. The service disconnect is there to disconnect (and control) the incoming power, but the rating of the service disconnect also provides protection for the feeder conductors. However, this rating can't be lower than specified in 230.79. The load side of the service disconnect can also be considered the point where the service requirements end and feeder requirements begin.
A structure can be served by only one service drop or service lateral as defined in Art. 100 [230.2]. The exceptions to this fall into four categories: special conditions, special occupancies, capacity requirements, and different characteristics.
If acceptable to the authority having jurisdiction (AHJ) [700.12(D) and 701.11(D)], you can place emergency power and/or legally required standby power on an additional service. The following are also permitted to be on additional services:
Optional standby power
Parallel power production systems
Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability.
If you have special permission from the AHJ, you can add services for:
Multiple-occupancy buildings, where there's no available space for supply equipment accessible to all occupants, or
A structure so large that two or more supplies are necessary.
You can add services where:
Capacity requirements exceed 2,000A,
Load requirements of a single-phase installation exceed the utility's capacity, or
You have special permission of the AHJ.
Additional services are permitted for different voltages, frequencies, or phases, or for different uses, such as for different electricity rate schedules.
If you use multiple services, install a permanent plaque or directory at each service disconnect location. This plaque must denote all other services supplying that structure. It also must denote the area served by each.
The service disconnecting means must be identified as suitable for use as service equipment [230.66]. This means the service disconnecting means is supplied with a main bonding jumper so that a neutral-to-case connection can be made, as required in 250.24(C) and 250.142(A). See Fig. 1. The service disconnecting means must open all service-entrance conductors from the structure premises wiring [230.70].
Install the service disconnecting means at a readily accessible location. This can be outside the structure. If you place it inside the structure, locate it nearest the point of service conductor entry. There's another factor to consider when locating a disconnecting means indoors — you can run the service entrance conductors only so far. These conductors do not have short-circuit or ground-fault protection. Thus, they must be limited in length when inside a building. Some local jurisdictions have a specific requirement as to the maximum length within a building. If yours doesn't have a specific requirement, get the approval of the AHJ before finalizing the location.
If you've ever seen a breaker panel in a restroom, you've seen a violation of 240.24(E). In addition, you can't install the service disconnect in a bathroom.
Some designers will use a remote-control device (shunt-trip) to actuate the service disconnecting means. There's nothing wrong with this, but the service disconnecting means must still be in a readily accessible location [230.70(A)(3)]. As before, this will be outside the structure, or — if inside — nearest the point of entry of the service conductors as required by 230.70(A)(1) [Fig. 2].
The service disconnecting means must be one of the following [230.76]:
Manually operated switch.
Circuit breaker capable of being operated manually.
Each service disconnecting means must plainly indicate whether it is in the open or closed position [230.77].
You can have no more than six service disconnects for each service permitted by 230.2. This rule also applies to each set of service-entrance conductors permitted by 230.40, Exception No. 1, 3, 4, or 5 [230.71].
The rule is six disconnecting means for each service, not six service disconnecting means per building. If the building has two services, you can have a total of 12 service disconnects (six disconnects per service).
The disconnecting means for power monitoring equipment, transient voltage surge suppressors, the control circuit of the ground-fault protection system, or power-operable service disconnecting means is not considered a service disconnecting means.
The service disconnecting switches or circuit breakers must be mounted in a single enclosure, in a group of separate enclosures, on a switchboard, or in a switchboard [230.71(A)]. If you have more than one disconnect at a service, all of them must be grouped. This way, the fire response team that finds one disconnect finds all of them.
An exception to this is pretty obvious if you think about it. Can you guess what it is? Here's a hint. You don't want this to be disconnected during a fire. It's the fire pump disconnect. Locate it remotely from the one to six disconnects for normal service . The disconnect for the following loads must also be remote from the normal service disconnects:
Legally required systems, or
Optional standby systems.
What is a remote distance? The NEC doesn't specify this distance, so it would be up the AHJ.
In a multiple-occupancy building, each occupant must have access to his or her service disconnecting means [230.72(C)]. But this requirement doesn't apply in multiple-occupancy buildings where electrical maintenance is provided by continuous building management. In such a case, the service disconnecting means can be accessible only to building management personnel.
Service overcurrent protection
The NEC doesn't require you to provide service conductors with short-circuit or ground-fault protection. What you must provide for each ungrounded service conductor is overload protection [230.90] located where the service conductors terminate [240.21(D)].
The rating of the protection device must not be greater than the ampacity of the conductors. Five exceptions apply:
Motors: Apply Article 430 requirements.
Where the ampacity of the ungrounded conductors doesn't correspond with the standard rating of overcurrent protection devices as listed in 240.6(A), you can use the next higher protection device if it doesn't exceed 800A [240.4(B)]. Example: Two sets of parallel 500-kcmil THHN conductors (each rated 380A at 75°C) can be protected by an 800A overcurrent protection device (Fig. 3).
The combined ratings of two to six service disconnecting means can exceed the ampacity of the service conductors — if the calculated load (per Art. 220) doesn't exceed the ampacity of the service conductors (Fig. 4).
Fire pumps: Apply Art. 695 requirements.
Overload protection for 3-wire, single-phase, 120/240V dwelling unit service conductors can conform to 310.15(B)(6).
A final comment on points one through five: While these requirements are providing just overload protection for the service conductors, the load side of these service disconnects are providing overload protection as well as short-circuit and ground-fault protection for the feeder conductors.
Have you noticed a common theme in the requirements for service equipment? Most of these point to achieving a single purpose, making it easy for fire response crews to disconnect the structure from incoming power. These people don't have time to be operating large numbers of disconnects, which is why you're limited to six per service. Nor do you want people wandering around trying to find those disconnects, which is why they are located near the point of entrance.
If you ask the question, “How can I make it easy for a fire response crew to disconnect power?” you will have most of the answers you need for a correct service installation. If you're in the equipment selection phase, look for ways to reduce the number of disconnects needed. Switchgear manufacturers have some excellent solutions that can help you achieve this goal.
Finally, don't forget to comply with the Chapter One requirements. These include limiting access to authorized personnel and providing proper working clearances.