How to Specify a 2000A UL 891 Switchboard for a US Project

For 2000A UL 891 switchboards, the most common voltage configurations are 480Y/277V 3-phase 60Hz and 600V 3-phase 60Hz. The voltage selection depends on the project electrical system design and utility supply.

• 480Y/277V: Most common for industrial and commercial applications in the US
• 600V: Common in Canada and some US industrial facilities
• 208Y/120V: Less common for 2000A applications, typically used for smaller switchboards

The available fault current at the switchboard installation point determines the required SCCR (Short-Circuit Current Rating). This calculation must include all upstream sources: utility transformer, generators, and any other power sources.

• Obtain utility fault current data from the electric company
• Calculate contribution from all generators and UPS systems
• Use IEEE 141 (Red Book) or IEEE 399 (Brown Book) methods
• Typical values: 40kA, 65kA, 85kA, 100kA, 150kA, 200kA

For a 2000A switchboard, the main bus rating is 2000A continuous. However, you must also consider future expansion and load growth. Some projects specify 2500A or 3000A bus for future flexibility.

• 2000A: Standard rating for this application
• 2500A: Provides 25% margin for future growth
• 3000A: Provides 50% margin, requires larger enclosure
• Consider load growth projections for the next 10-20 years

The main breaker configuration depends on the number of power sources and the required redundancy. Common configurations include single main, double main (main-tie-main), and main-tie-main with dual power sources.

• Single Main: One main breaker, one power source
• Main-Tie-Main: Two main breakers with tie breaker, two power sources
• Double Main: Two main breakers without tie, separate bus sections
• For data centers: Main-tie-main is typical for Tier III and IV

For 2000A switchboards, the main breaker is typically an air circuit breaker (ACB) rated per UL 1066. Feeder breakers can be MCCB (UL 489), ICCB, or ACB depending on the rating and application.

• Main Breaker: ACB (UL 1066), 2000A frame, adjustable trip
• Feeder Breakers > 800A: ACB or ICCB
• Feeder Breakers 100A-800A: MCCB or ICCB
• Feeder Breakers < 100A: MCCB
• Consider selective coordination requirements

The enclosure type depends on the installation environment. Indoor electrical rooms typically use NEMA 1, while outdoor installations require NEMA 3R with rainproof construction.

• NEMA 1: Indoor, general purpose, electrical room installation
• NEMA 3R: Outdoor, rainproof, drip shields, conduit hubs
• NEMA 12: Indoor, dust-tight, for dirty industrial environments
• Consider seismic bracing for high seismic zones

Modern switchboards require comprehensive metering and protection. Specify power meters, current transformers, potential transformers, surge protective devices, and ground fault protection as needed.

• Power Meters: Voltage, current, kW, kVA, kVAR, power factor, energy
• Current Transformers: For metering and protective relaying
• Surge Protective Devices: Type 1 or Type 2 for transient protection
• Ground Fault Protection: Required per NEC 230.95 for certain applications
• Communication: Modbus, BACnet, EtherNet/IP for BMS integration

The single-line diagram (SLD) is the most important document for switchboard specification. It shows all electrical components, connections, ratings, and protective devices. A complete SLD ensures accurate quotation and proper equipment design.

• Show all main and feeder breakers with ratings
• Include CT/PT locations and ratios
• Show metering and protection devices
• Indicate available fault current at each point
• Note selective coordination requirements
• Include NEMA rating and special requirements