Category Archives: Field Service
The Institute of Electrical and Electronics Engineers (IEEE)’s White paper on Protective Devices and Maintenance states that “Industry Standards for an manufacturer’s of LV power circuit breakers recommend a general inspection and lubrication after a specified number of operations or a least once per year” and “most requirements for LV circuit breaks apply to MV breakers as well. Manufacturers recommend that these breakers be removed from service and inspected at least once per year”. Similar to other aging infrastructure systems in the US, very little maintenance and testing is done to electrical systems, with many LV systems never seeing period maintenance at all. This is very alarming when you consider that electrical personnel have been injured by arc flash incidents where arc flash prediction was Category 0 because upstream breakers failed to trip. A poorly maintained electrical system is a serious hazard present to all who work on or around it, and should not be neglected. “Several studies have shown that LV power circuit breakers which are NOT maintained within a 5 year period, have an average of 50% failure rate”, also stated by IEEE.
Need some help backing up your concerns to decision makers within your facility? Consider the following:
• The 2012 edition of NFPA 70E states “The arc flash hazard analysis shall take into consideration the design of the overcurrent protective device, including its condition of maintenance”. Refers to Section 21.10 of NFPA 70B-2006 for maintenance of protective devices; this section specifies overcurrent time-current testing of the protective devices.
• NFPA 70E Article 205.3, General Maintenance Requirements, states, “Electrical equipment shall be maintained in accordance with the manufacturer’s instructions or industry consensus standards to reduce the risk of failure and the subsequent exposure of employees to electrical hazards.”
Several recent studies have determined that failure rates of LV circuit breakers are increasing, after only a few years of use. One recent survey states that 23% of circuit breakers tested had an issue affecting the protective device operations and over 10% did not function at all. We should assume that all older gear that have not been maintained in accordance with NETA MTS or NFPA 70B, will trip per their overcurrent time-current curves. Such a critical assumption would likely not be included as a description on the equipment arc flash warning label. An arc flash calculation based on actuation of a protective device that has never been maintained will not present accurate and correct data in the models or on the labels. The calculated incident energy depends on how long it takes an upstream protective device to sense, respond to, and eventually clear the arcing fault. If the breaker hasn’t been maintained and tested as required, there is no assurance that it will respond in accordance with its published time-current curve.
Before beginning an Arc Flash Study for your facility, determine whether or not your equipment maintenance has been performed at the acceptable level. If not, there is no promise that the circuit breakers will actually respond to their time-current curves or if they are capable of opening properly at all. It’s important to confirm that Arc Flash calculations are performed using correct data, on properly maintained equipment, so that the arc flash ratings are correct. The safety of personnel depends on it.
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