Working Safely Near Switchgear

My plan for blog topics over the next few months is to focus on working safely around various types of electrical distribution equipment.  The equipment that I will discuss will be based on what I have used and found effective at keeping people safe when working near exposed live (energized) circuits.

So, let’s get going with the topic of working safely near switchgear.

“A switchgear assembly [is] completely enclosed on all sides and top with sheet metal…and 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…” [1].

In the US, switchgear are evaluated to Underwriters Laboratories (UL) Standard for Safety for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear, UL 1558, American National Standard Institute (ANSI) Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear, ANSI C37.20.1, and Standard for Conformance Testing of Metal-Enclosed Low-Voltage AC Power Circuit Breaker Switchgear Assemblies, ANSI C37.51.  The short circuit current and withstand testing of switchgear requires that unfused devices be tested to a short circuit current with a power factor of 15 percent for 30 cycles [1].  The short circuit current is determined by the manufacturer, but it must be equal to or greater than the calculated fault current at the point of installation [2].

When working, testing, adjusting, calibrating, or servicing switchgear, specific precautions should be observed.  

The safest method to work on or near switchgear is to de-energize the switchgear and effectively control all hazardous energy through a comprehensive lockout tagout (LOTO) program.  To ensure the switchgear remains de-energized, short all phase conductors to the grounding conductor with an appropriately rated conductor while the switchgear is de-energized.

Arcing hazards (arc flash and arc blast) can occur when energizing or de-energizing components within the switchgear, or the switchgear itself.  To reduce the risk associated with energizing or de-energizing switchgear, operating procedures and personal protective equipment (PPE) is required.  Common safe work practices include:  

• Conduct a risk assessment to identify potential hazards
• Having two qualified employees (one employee who is doing the work and one who is the first responder) conducting work
• Having qualified employees using appropriate PPE
• Having qualified employees use tested and inspected tools and equipment
• Energizing or de-energizing equipment a safe distance (but within sight)
• Energizing or de-energizing equipment from the side
• Having qualified employees create and follow safe work practices

When working on switchgear near exposed live (energized) circuits, arcing and shock hazards are present.   Adding additional equipment when the switchgear is energized is not advised.  However, testing, calibration, and adjustment of protection and control devices, power switching components, and measurement devices are common.

To mitigate shock and arcing hazards when working on energized switchgear, safe work practices and PPE is required. In addition to the safe work practices identified above, additional best practices include:  

• Ensure that all qualified employees remove all metal or loose objects
• Ensure that qualified employees understand the construction, operation, and installation of the equipment
• Having qualified employees use equipment intended for the application (proper voltages, dielectric withstand, etc.)
• Limiting the number of people within the arc flash boundary and shock hazard boundaries
• Identify contingencies to address how additional measurements or adjustments are going to be communicated and acted upon

Best practices for working around energized equipment has changed significantly with the introduction of the requirement to add arc flash labeling that was introduced with the 2002 edition of the National Electric Code and the publication of NFPA's Electrical Safety in the Workplace, NFPA 70E.  Changes are also occurring as equipment and component manufacturers introduce new technologies designed to increase safety in the workplace.  Increased workplace safety requirements are also be adopted by organizations for their employers and any vendor or contractor working on their property.

To assist people with working in new or unfamiliar facilities or locations, I have created an on-line Day-One-Safety checklist.  The Day-One-Safety checklist can run from a PC, an iPhone or an Android phone.  There is no cost to use this program.  To request a password or to Login, clickhere.

References:

1.     Underwriters Laboratories, Standard for Safety for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear, Fourth Edition, UL 1558, 1999 February, Northbrook, IL USA.

2.     National Fire Protection Association, 2014 National Electric Code, NFPA 70-2008, Quincy, MA USA