Application Q&A: Selecting and identifying ‘service equipment’ that is in compliance with NEC rules.

Understanding the National Electrical Code rules governing the configuration of Service Equipment switching and overcurrent protection can help prevent costly mistakes in the design of metal-enclosed switchgear. Non-compliance with National Electrical Code Article 230, entitled “Services,” is one of the most common reasons for failure of newly installed switchgear to pass field inspection. An easily made mistake is that of exceeding the six-switch rule. Other violations include failure to provide a service disconnect or overcurrent protection device. Proper labeling of the switchgear may have been omitted. In such cases, the switchgear may have to be fixed in the field or returned to the factory, incurring considerable expense and loss of time.

The questions and answers that follow will explain some NEC rules as they apply to metal-enclosed switchgear service equipment, and may help you avoid design pitfalls such as those mentioned above.

How do I identify what is considered ‘Service Equipment’ according to the NEC?

To identify the Service Equipment you must first be able to locate the Service Point.

What and where is the Service Point?

The Service Point is the point of connection between the facilities of the serving utility and the user’s premises wiring. This connection can occur within a switchgear enclosure.

What is the relationship between the Service Point and the Service Equipment?

The service equipment is the first switchgear downstream from, or containing, the service point.

What is the function of the Service Equipment?

The Service Equipment protects the utility from faults on the customer’s system and provides a means of isolating the customer from the utility conductors.

What does the Service Equipment consist of?

The NEC code states that the Service Equipment must include the following:

One or more service disconnect switches up to a limit of six. All three poles of a service disconnect must open simultaneously.
Overcurrent protection on the load side of and in close proximity to the service disconnect. The overcurrent protection may be an integral part of the service disconnect.

Can you give me an example of a Service Disconnect?

Where permissible, a feeder interrupter switch within metal-enclosed gear such as an S&C Mini-Rupter® Switch, Alduti-Rupter® Switch, or Vista® load-interrupter switch can provide the Service Disconnect. A draw-out circuit breaker can also fulfill this function.

Are there any types of switches that cannot be used as Service Disconnects?

Yes. Since the NEC Code requires that all three poles of the service disconnect open simultaneously, single-pole devices such as Uni-Rupter®-equipped fuses and TransFuser™ mountings cannot be used as service disconnects.

What’s all this about the ‘limit-of-six-switches’ rule?

The NEC code specifies a limit of six interrupter switches in a given metal-enclosed switchgear assembly if it is the service equipment. Within this six-switch limit, the feeder interrupter switches can be considered the service disconnects and the fuses or fault interrupters associated with each switch can be the required overcurrent protection. Here are two examples of acceptable service equipment configurations:

Example 1: In this example, the Service Point is in a bay of metal-enclosed switchgear. The switchgear is also the service equipment. The feeder-interrupter switch functions as the service disconnect, and the fuse provides the required overcurrent protection.

Example 2: The service point is again in the main switchgear. Since the main switchgear has fewer than six feeder interrupter switches, the feeder-bay switches can be considered Service Disconnects. The feeder-bay fuses provide the overcurrent protection, and the entire assembly is the Service Equipment. (The incoming switch is used to isolate the switchgear during maintenance.)

Which S&C Switchgear can be used as Service Equipment?

S&C Pad-Mounted Gear and Vista® Underground Distribution Switchgear ways can be used as Service Equipment. Both can be configured to provide the service disconnect and overcurrent protection. And since pad-mounted gear has only four compartments and Vista UDS has only six ways, it would be impossible to exceed the six-switch rule.

In the case of S&C Metal-Enclosed Switchgear and System VI™ Switchgear, it is possible to identify each feeder interrupter switch as a service disconnect if the gear has no more than six feeders. Fuses or fault interrupters would provide the short-circuit protection.

What do you do if a switchgear assembly has more than six feeder bays? How do you provide the Service Equipment?

If the switchgear assembly has more than six feeders — or ultimately will have more because it includes provisions for future extension — a main disconnect switch with an associated fuse or fault interrupter must be provided in an entrance bay. Thus, metal-enclosed switchgear or System VI Switchgear with more than six feeder switches can be considered the service equipment if it has a service entrance as just described.

Example 3: In this example, the service point is in the main switchgear, but the switchgear has more than six feeder interrupter switches. Here, the incoming switch is the service disconnect and must be provided with fuses for overcurrent protection. The entire switchgear assembly, including the incoming switch and feeder interrupter switches, is the service equipment.

Can metal-clad switchgear function as the Service Equipment in a system with metal-enclosed switchgear?

Yes. The following is a typical application of circuit breakers as service equipment.

Example 4: The service point is in the metal-clad gear, and the metal-clad gear is also the service equipment.The metal-clad switchgear is the main switchgear feeding units of metal-enclosed switchgear.

What about labeling for the Service Equipment?

The NEC Code requires that the Service Equipment be permanently marked and suitable for the application and environment in which it is installed. For S&C Switchgear, a “Service Equipment” sign is available upon request from Application Engineering—Metal Enclosed Gear Products Division. This sign is not typically furnished with shipments of S&C gear, since the gear may not actually be the service equipment at a particular installation.

Does service equipment need to be UL listed?

This is not possible. UL does not list gear for specific applications such as service entrances. The UL listing mark certifies that the following conditions have been met in accordance with the appropriate standard:

The equipment has the necessary ratings.
The ratings have been proven by test.
The equipment has the required construction features.

Do NEC rules apply in all circumstances?

There’s no escaping it . . . when the end user is not an electric utility, NEC requirements apply to metal-enclosed switchgear. The information presented in this article covers just one aspect of these rules. For help in choosing switchgear, contact your local S&C Electric Company sales representative.