How many times have we heard that question? Or had a customer ask you to evaluate the condition of their switchgear only to arrive on site to find out they don’t have switchgear; they have switchboards. Or worse yet you’re discussing upcoming work at their plant and the conversation alternately refers to the same piece of equipment as switchgear and a switchboard in the same conversation. Is switchgear a generic term or is the issue a simple matter of confusion? Unfortunately, the term is often used incorrectly by electricians, architects, and even engineers, to mean any piece of low voltage distribution equipment. So, what is the difference, and does it really matter?

 

Probably the easiest way to distinguish between a switchboard or a piece of switchgear is by voltage level. Typically, switchboards are designed for applications rated at 600-volts or less. The more versatile and robust switchgear is designed to handle higher voltages. Consequently, the construction, hardware, and design are different.

 

Switchgear generally has drawout breakers that can be replaced or withdrawn during system operation. Switchgear’s construction is usually fully compartmentalized with grounded metal barriers around any live components. Protective shutters, insulated bus, and mechanical interlocks round out the design which includes protective features and devices commonly used to regulate the flow of electricity such as arrestors, fuses, isolators, circuit breakers, relays, and disconnect devices.

 

The 2017 National Electric Code (NEC), in Article 100, defines Switchgear as: “An assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) containing primary power circuit switching, interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both”. The informational note which follows provides further clarification that switchgear 1000V or less may be identified as “low voltage power circuit breaker switchgear” while gear rated at 1000V and above is designated “Metal clad” or “Metal enclosed” switchgear. 

 

OK. So, what’s different about a Switchboard? The 2017 NEC defines a Switchboard as: “A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets”.

 

So, a switchboard is simply a lighter and less expensive panel with buses, switches, protective and electrical control devices mounted on the front or back, or on both, used to distribute power to transformers, panel boards, individual loads and control equipment. Essentially, you can think of Switchboards as large panel boards and switchgear as a more functional and robust piece of electrical equipment providing centralized control and monitoring, offering more “bells and whistles” with features, such as rackable breakers. Are there any other notable differences?

 

Well, you should be aware that Switchgear and Switchboards are built to different standards:

  •  Switchgear structures are built and tested according to IEEE/ANSI standard C37.20.1, UL standard 1558, and NEMA standard SG-5,
  • While Switchboards are built and tested according to NEMA PB-2, and UL -891.

 

·        Low voltage switchgear typically only incorporates Low Voltage Power Circuit Breakers (LVPCB) which conform with ANSI C37.13, NEMA SG-3 and are listed per UL-1066 and as an added benefit LVPCB allow for remote operation.

  • Switchboards are often found with a combination of protective devices that can range from insulated case (ICCB) to molded-case circuit breakers (MCCB) which are listed per UL-489, they may include fusible switches listed per UL-508 and 977 as well as power circuit breakers listed to UL-106 6.

 

A key difference is that the switchgear, tested under UL 1558, establishes a short-time 30-cycle (0.5 second) withstand rating; while switchboards are tested and rated (under UL581) at 3-cycles. (0.05 seconds). The 30-cycle delay allows downstream breakers to operate first; providing selective coordination and permitting the use of switchgear breakers without an instantaneous function. This characteristic enhances critical system reliability and is mandated by the NEC for emergency systems, legally required standby systems, and Critical Operation Power Systems.

 

The decision to use switchgear or a switchboard is based on the application, budget, serviceability requirements, and required capabilities. Typically, more critical operations specify switchgear.

 

Switchgear construction can be indoor or outdoor and can be found in three classes based on voltage levels: Low voltage switchgear, Medium voltage switchgear, and high voltage switchgear. Another way to keep it straight is to remember Switchgear is generally installed at the highest level of the power system. From there cables feed power from the switchgear into other switchboards. So, now you know…