CSE Pure Power - Summer 2008 - (Page 36)

❯❯ PURE POWER // SUMMER 2008 36 switchgear story ARC-RESISTANT STANDARD When an arc fault occurs within a conﬁned space, such as a circuit breaker compartment within a switchgear section, the arc energy is converted into heat, resulting in a rapid pressure increase than can cause an explosion that will heavily damage the switchgear and endanger nearby personnel. As deﬁned in ANSI/IEEE C37.20.7-2007, the intention of arc-resistant switchgear is “to provide an additional degree of protection to the personnel performing normal operating duties in close proximity to the equipment while the equipment is operating under normal conditions.” (See ANSI/IEEE C37.20.7, section 1.2.2) According to the standard, normal operating conditions entail: Opening or closing switching devices Connecting and disconnecting withdrawable parts Reading of measuring instruments and monitoring equipment. This is a performance standard, not a construction standard. It does not specify how switchgear should be built to increase arc resistance, but rather what the results in a test laboratory must be in order for switchgear to be considered arc resistant. It even goes a step further by declaring it does not apply to personnel working in, on, above, or below the equipment, including: On top of the switchgear for cleaning and maintenance Activities that require a person to be elevated above the base level of the switchgear via a ladder, lift, or on a catwalk Switchgear installed on an open grate Installations over a cable vault large enough for someone to enter the vault. Because ANSI/IEEE C37.20.7 does not dictate how arc-resistant construction should be achieved (though a 2007 revision does provide guidelines in this area), facility owners have more latitude beyond the traditional method of using a vented sheet-metal enclosure to protect the switchgear, which is essentially a passive solution. True, it will likely protect personnel walking by or working in close proximity of the switchgear from the effects of an arc fault, which is what it’s designed to do, but when the arc fault has ﬁnally been cleared, chances are the equipment will be damaged beyond repair. That could mean a facility owner’s concerns have just begun. It’s possible the affected switchgear sections could be rebuilt, but depending on the extent of the damage, that could take a couple of days to a couple of weeks. For more info, enter #414 on the Reader Service Card http://www.sens-usa.com http://www.sens-usa.com

Table of Contents Feed for the Digital Edition of CSE Pure Power - Summer 2008

CSE Pure Power - Summer 2008 Contents In the News Industry Roundup Risk Assessments for COPS Grounding Requires More Power Systems to Protect Healthcare Important Changes Coming in NFPA 70E A Look at Arc-Resistant Switchgear Agencies and Associations New Products Ad Index

CSE Pure Power - Summer 2008

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