Switchboards – Installation Requirements and Pre-Energization Steps

Last month I discussed working safely near switchgear.  This month I will continue focusing on the requirements of distribution equipment and discussing items related to working safely near switchboards.

A switchboard is defined 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” [1].  Switchboards are generally accessible from the front and rear of the cabinet, and are not intended to be installed in other cabinets.  In the US, switchboards are evaluated to UL’s Standard for Safety, Switchboards, UL 891.  UL 891 is a North American harmonized standard between Underwriters Laboratories, the Canadian Standards Association, and Mexico’s Association for Standardization and Certification.  It is best practice to have all switchboards Listed by an Occupational Safety and Health Administration (OSHA) nationally recognized testing laboratory (NRTL).  NRTL’s include UL, ETL, MET, CSA and a number of others.

Switchboards are required to be installed in accordance with all national, state, and municipal codes.  Installation requirements include those detailed in the National Electric Code and include [1]:

• The short circuit current rating (SCCR) of the equipment shall equal to or greater than the fault current at the point of application, NFPA 70, Article 110.10,
• Equipment shall be marked with Arc-Flash warning signage, NFPA 70, Article 110.16,
• Switches, circuit breakers (CBs), and overcurrent protective devices shall comply with other articles within the National Electric Code, e.g. Articles 240, 250, 312, 404, etc., NFPA 70, Article 408.2
• All circuits shall be clearly marked and identified, NFPA 70, Article 408.4
• Equipment shall have suitable space (clearance), NFPA 70, Article 408.18

Basic steps should be taken prior to energizing the switchboard.  Some of the steps can be found in the installation instructions from the manufacturer.  Other steps are from the National Electrical Manufacturers Association (NEMA).  Pre-energization steps include:

• Ensure all blocks, spacers, and packing materials are removed
• Ensure all internal bus bars and connections are tightened (torqued) to specifications
• Ensure all grounding conductors are connected
• Manually exercise all switches, circuit breakers and other operating mechanisms
• Visually check all phase conductors to ensure that they are landed on the proper phase terminals
• Conduct an insulation resistance or megger test on all conductors coming to or leaving the switchboard
• Conduct a test to ensure that any ground fault protection system is operational
• Set any electronic trip circuit breakers to the proper values
• Remove any foreign material
• Set all switches or circuit breakers to the OFF or de-energized position
• Ensure all panels are installed and all panel mounting screws are installed

Once the pre-energization steps have been completed, a risk assessment should be conducted to identify any potential hazards and the appropriate mitigation techniques associated with the energizing of the switchboard shall be conducted.  Included in the risk assessment should be the steps and the order in which those steps will occur.

Energizing the switchboard shall be conducted by qualified personnel only.  Qualified personnel are defined as those persons who have the skills and knowledge of the construction, installation, and operation of the equipment and someone who has been trained to recognize and avoid the hazards associated with working on the equipment [3].

Even though the panels on the switchboard are properly installed, arcing hazards can occur that can injury anyone in the area of the switchboard.  To reduce the likelihood of injury only qualified personnel should be in the vicinity of the switchboard.  All qualified personnel who are inside the arc flash boundary are required to wear arc flash protection.  The arc flash boundary and the level (Category) of arc flash protection required depends on the incident energy available at the switchboard.  This can be calculated using software tools (e.g. SKM, ETAP, EasyPower) or through the tables listed in NFPA 70E.

For next month, I will continue examining distribution equipment.  I have not completely decided on the equipment, but I leaning towards busways, transformers, or surge protective devices (SPDs).  

To assist people with working in new or unfamiliar facilities or locations, use the Day-One-Safety checklist.  This is a free on-line checklist available to anyone who wants would like to use it.  To request a password or to Login, click here.

References:

1. National Fire Protection Associated (NFPA), National Electric Code, NFPA 70-2014, Quincy, MA USA
2. National Electrical Manufacturers Association (NEMA), General Instruction for Proper Installation, Operation, and Maintenance of Panelboards Rated 600 Volts or Less, NEMA PB 1.1 2007, Rosslyn, VA USA
3. National Fire Protection Association (NFPA), Standard for Electrical Safety in the Workplace, NFPA 70E-2012, Quincy, MA USA