|Historically, have we adequately maintained critical electrical equipment, and have we defined what is “critical”? Is the maintenance priority “reliability” and ensuring equipment isn’t damaged? Have we ever considered doing maintenance to limit arc flash incident energy and protect workers?|
The CSA Z462 Workplace Electrical Safety standard — one of the most popular in 2009 after its publication on Dec. 28, 2008 — is cause to re-evaluate these questions. If you are not familiar with this standard, you will be as it moves across Canada and becomes the accepted consensus-based standard for identifying and managing the electrical hazards of arc flash and shock.
Arc flash had little to no profile in Canada until the 2004 edition of the NFPA 70E Standard for Electrical Safety in the Workplace was published and some industries in Canada became aware of its existence. (CSA Z462 is the Canadian adaptation of NFPA’s 70E 2009 edition.)
Simply put, an arc flash is a toxic energy release related to abnormal conditions in energized electrical conductors or circuit parts. Four key factors determine the severity of an arc flash: the available short circuit fault current, how much energy is present, the clearing time of the electrical fault and the distance the worker is away from the point of the arc flash event.
One may think this hazard is only related to high-voltage electrical equipment (greater than 750 volts), but it is not the case. In fact, low-voltage equipment (such as those at 480 or 600 volts) will most likely have higher arc-flash incident energy than the high voltage equipment, as the available fault current is higher.
Electrical workers may be exposed to the arc flash hazard when working on energized panel boards, switchboards, motor control centres, switchgear and utility power distribution systems. Critical to eliminating or reducing the risk of exposure is ensuring electrical protective devices operate as intended. This is where electrical maintenance needs to focus its attention.
Maintenance of electrical equipment and its protective devices is critical to eliminating the probability of an arc flash event from occurring or, if it does occur, to reducing the amount of thermal energy released. A lack of maintenance can increase the probability of an event, negatively impact clearing time and cause an increase in incident energy, which results in the release of thermal energy that can burn skin.
Poor electrical maintenance can also compromise the gap between energized electrical conductors and circuit parts, causing an arcing fault condition that must be cleared by a protective device, such as a circuit breaker or a fuse. Maintaining these protective devices, which detect problems and open to clear an arcing fault, is critical to eliminating or reducing arc flash incident energy.
CSA Z462 identifies the need to complete arc flash hazard analysis, and one of the methods available is engineering-based calculations. In Clause 4.3.3, the standard explicitly recognizes the importance of electrical-equipment maintenance: “Improper or inadequate maintenance can result in incorrect opening time of the over-current protective device, thus increasing the incident energy.” Additionally, Clause 5.3.5 highlights potential consequences: “Protective devices shall be maintained to adequately withstand or interrupt available fault current. Note: Failure to properly maintain protective devices can have an adverse effect on the arc flash hazard analysis incident energy values.”
See CSA Z462 Annex B, “Safety related electrical maintenance,” for an example and more information on the importance of electrical-equipment maintenance to enhancing safety with respect to energized electrical equipment. It summarizes the importance of minimizing electrical fault clearing time. Additionally, where the electrical distribution system requires it, companies could use a more analytical method like reliability-centred maintenance to identify the maintenance strategies deployed in ensuring clearing times of protective devices are maintained and minimized.
Companies need to review their current electrical-equipment maintenance strategies and ensure they identify critical equipment and ensure they complete required maintenance to manufacturers’ specifications and industry-accepted electrical equipment maintenance standards, such as NFPA 70B Recommended Practice for Electrical Equipment Maintenance and the International Electrical Equipment Testing Association (NETA) Standard of Maintenance Testing Specifications.
If you don’t think your current electrical-equipment maintenance strategies are adequate, start by ensuring your single-line diagrams are as built, establishing a thermography program (baseline with regular intervals and create a trend to look for anomalies), performing regular inspections, exercising breakers/switches and ensuring original breaker/relay settings are current and tested.
CSA Z462 recommends, at a minimum, companies review completed engineering-based arc flash hazard analyses at least every five years or when significant changes have occurred to an electrical system. At a minimum, companies need to ensure critical electrical protective devices, such as main breakers and sub-feed breakers, are inspected, maintained and tested at acceptable frequencies.
The emergence of CSA Z462 has heightened Canadians’ awareness of the severity of an arc flash incident to workers if and when it occurs. In reviewing how to eliminate or reduce the incident energy released, companies must reduce the clearing time of an arcing fault, and this can only be guaranteed by completing regular maintenance on critical electrical protective devices and electrical equipment.
Terry Becker, P.Eng., is the owner and senior management consultant of ESPS Electrical Safety Program Solutions Inc. (www.esps.ca) in Calgary. He was the first vice-chair of the CSA Z462 Technical Committee, is currently an Executive Committee Voting Member, and is a Working Group Leader for the annexes. He can be reached by email at firstname.lastname@example.org or by phone at (403) 465-3777.