Select your location

Switchboards: fundamentals of switchboards

What is an electrical switchboard? 

Switchboards are used to safely distribute electricity throughout commercial and industrial facilities. A switchboard is a component of an electrical distribution system which divides an electrical power feed into branch circuits while providing a protective circuit breaker or fuse for each circuit in a common enclosure.

Switchboards typically have a maximum voltage rating of 600 Vac/Vdc and a maximum bus rating of 6000 A and are designed to meet UL891 and NEMA Standard PB2. 

What is a service entrance switchboard? 

Switchboards provide power downstream in the electrical system either directly to large loads or to panelboards that will further divide the power to smaller branch circuits to feed smaller loads. In smaller facilities, the switchboard may be fed directly from the electrical utility, in which case it is referred to as a “service entrance” switchboard. Local electric utility companies typically have specific requirements for service entrance switchboards. In large commercial or industrial facilities, a switchboard will receive power from an upstream circuit breaker mounted in a switchgear assembly. 

Man-working-on-breaker-enlarged
pow-r-line-1a-open-panelboard

What is the difference between switchboards and panelboards? 

Switchboards and panelboards provide similar functionality in a power distribution system. Panelboards are typically limited to a maximum of 1200 A incoming current (main), either flush mounted within a wall or surface mounted to a wall. Switchboards are freestanding units that can be front connected and which would require only front access, similar to panelboards..

However, switchboards can allow for both front and rear access if desired. Switchboards can contain bussing and overcurrent devices up to 6000 A. While panelboards are designed to UL 67, switchboards are governed by UL 891. 

Switchboard structures 

A switchboard can consist of a single vertical structure or multiple structures depending on the number and sizes of the loads being powered.   

A main structure will contain the main disconnects or main lugs and will often contain utility and/or customer metering equipment and surge protection.  

Cabling can enter directly into the main structure or through a dedicated pull structure. Pull structures are commonly used in service entrance switchboards. Cables can enter the structure from the floor (bottom entry) or from above (top entry.)  

Distribution structures divide and send power to branch circuit protection devices and then to branch circuits to power downstream loads. Power flows from the main structure to the distribution structure via cross bus. 

In most installations, switchboards are mounted close to a wall and are front accessible only. If required, the switchboard can be constructed to allow both front and rear access. Rear access switchboards provide easier access for installation and maintenance, but they are typically deeper than front access only switchboards.  

The primary components of a switchboard structure are the frame, bus, overcurrent protective devices, instrumentation, enclosures and exterior covers. The switchboard frame is the metal skeleton that houses all the other components. The bus, which is either copper or aluminum, is mounted within this frame. The bus distributes power from the incoming cable conductors to the branch circuit devices. A horizontal bus distributes power to each switchboard section. In contrast, a vertical bus distributes power to the circuit protection devices within an individual section. 

Types of switchboards 

General purpose switchboards

General purpose switchboards can include integrated insulated case circuit breakers, molded case circuit breakers, fused switches, metering and surge protection. The vast majority of switchboard applications can be served with a general purpose switchboard.

Fusible switchboards

Fusible switchboards are designed for commercial, industrial, and service entrance applications to protect and switch feeder and branch circuits. Each panelboard unit includes a switching contact structure with an instantaneous trip element.

Commercial metering switchboards

Commercial metering switchboards combine circuit breakers, chassis, surge protection and meter sockets in a single, engineered assembly. Metering can be either bulb-type watt-hour meters or electronic tenant metering, as required by the utility.

Commercial metering switchboards are available for EUSERC and non-EUSERC utility metering requirements and provide electrical system distribution and metering for shopping centers, office buildings and other commercial multi-metering applications. 

Instant switchboards are a specialized commercial metering switchboard designed expressly for EUSERC markets. Instant switchboards are available as stock for quick shipment and include utility metering provisions, a fused main switch and breaker, as well as panelboard components. Instant switchboards are design for indoor or outdoor service and meet UL891 as well as EUSERC requirements.

Draw-out molded case switchboards

Draw-out molded case switchboards provide the same basic capabilities as a general purpose switchboard, with the added functionality of offering draw-out capability for one or more feeder breakers.  Draw-out molded case switchboards are often applied in critical applications like healthcare and data centers to reduce system downtime when replacing a breaker. 

 

Pow-R-Line XD switchboard

In recent years, draw-out capability in switchboards has been expanded to include molded case circuit breakers and power breakers typically found in low voltage switchgear assemblies. These switchboards provide higher density and a reduced footprint while accommodating higher current rated power breakers, and they require rear accessibility to barriered cable compartments. Eaton offers this capability in our Pow-R-Line XD switchboard.

Integrated Facility System (IFS)

Switchboards can be expanded beyond their basic circuit distribution and protection functions to include various other equipment as part of an Integrated Facility System (IFS). For example, IFS systems will often include low voltage distribution transformers, automatic transfer switches, uninterruptable power supplies and datacomm equipment.

By integrating the various equipment on the factory floor, IFS systems reduce footprint and installation time at the customer site. IFS type solutions are popular in multi-site applications like chain stores and restaurants, and in general construction where pre-fab solutions are expanding.

Watch video to learn more about Integrated Facility System (IFS)

    Generator quick connect switchboards

    Generator quick connect switchboards are specialized switchboards designed to allow safe and fast connection of a mobile generator to a building’s electrical system.  

    Customized solutions, customized service

    Regional satellite locations provide manufacturing of local, custom, and quick-ship panelboards and switchboards

    Interested in learning more?