Why this is not the time to ignore your electrical power system .
NFPA Journal®, July/August 2009
The current economic climate has us focused on infrastructure improvement, but few improvements are better for your electrical power system than maintaining your existing equipment. In these tough economic times, there may be a tendency to try to "save" on maintenance costs by postponing necessary upkeep. But this is a false savings, particularly as there is a direct connection between maintenance and electrical safety. When equipment fails, operators may be injured.
Several sources of information about maintaining the elements of a power system are available. One is Chapter 2 of NFPA 70E®, Electrical Safety in the Workplace®, which consists of four pages that essentially list the equipment you need to maintain.
Another is the 2006 edition of NFPA 70B, Recommended Practice of Electrical Equipment Maintenance, which covers the when and how of maintenance. Several chapters of NFPA 70B are "how" chapters devoted to each type of equipment. The "when" information in NFPA 70B is found in Annex I. The fine print note (FPN) after Section 200.1 also suggests referring to ANSI/NETA MS-2007, Standard for Maintenance Testing Specification, for guidance on maintenance frequency, methods, and tests.
Although all electrical equipment needs to be maintained, the most important, from a safety standpoint, are the overcurrent devices that trip circuits when a fault occurs. These determine the length of time the overcurrent conditions exist, which determines the amount of heat, energy, and damage that will occur.
The importance of properly maintaining overcurrent devices is mentioned twice in NFPA 70E. The first instance is in the FPN after Section 130.3, which notes that "improper or inadequate maintenance can result in increasing the opening time of the overcurrent protective device, thus increasing the incident energy." The second is in the FPN after Section 210.5, a reminder that "failure to properly maintain protective devices can have an adverse effect on the arc flash hazard analysis incident energy values."
An important consideration of a hazard/risk analysis, which NFPA 70E requires, is knowing when the equipment was last maintained, since the outcome of the analysis will be different depending on whether the equipment has had the required maintenance.
Of course, all electrical equipment, not just overcurrent devices, must be properly maintained. When a worker opens a 4k metal-enclosed, fused disconnect switch, for example, it is important that the switch open completely. If the main switch opens but the arcing finger sticks in the arc chute, part of the equipment will be energized, even though the switch itself appears to be open. If the equipment is jarred when the door is opened, the arcing finger may be released and initiate an arc fault. Even worse, the equipment may remain partially energized because the arcing finger is still stuck.
Section 210.5 of NFPA 70E addresses the maintenance of protective devices, while Section 21.10 addresses field testing molded case breakers, low-voltage power circuit breakers, and protective relays. Annex I recommends a one- to two-year interval for cleaning, calibrating, and function testing electromechanical relays, an interval that can be increased to three years for solid-state devices.
When production is slow, managers like to keep their people busy, and what better way to keep people busy than have them perform preventive maintenance? Now is not the time to cut back on maintaining your electrical power system. Now is the time to improve your electrical system infrastructure using the safe practices of NFPA 70E and the maintenance recommendations of NFPA 70B.
Bill Buss is senior electrical engineer for NFPA and is staff liason for NFPA 70E.