The new edition of this electrical equipment maintenance standard includes major changes/additions, mostly on power quality and electronic equipment.
A must-read standard for electrical equipment maintenance, NFPA 70B has been revised and updated. It's now available, in the 1998 edition, for your immediate use. Although many of the extensive changes, additions, corrections, and deletions are editorial or minor, there are significant additions you should be aware of.
Chapter 4 (Planning and Developing an Electrical Preventive Maintenance Program). Section 4-2.3 (Diagrams and Data) now includes a qualifying statement about training personnel who do maintenance testing of protective equipment (relays and series or shunt-trip devices).
(e) Personnel performing the tests should be trained and qualified in proper test procedures. Various organizations and manufacturers of power and test equipment periodically schedule seminars where participants are taught the principles of maintenance and testing of electrical protective devices.
Authors define the scope of training, based on NFPA 70E, Electrical Safety Requirements for Employee Workplaces.
Chapter 5 (Fundamentals of Electrical Equipment Maintenance). Section 5-1 (Design to Accommodate Maintenance) emphasizes the safety aspects of conducting inspections, tests, repairs, and servicing. It includes this new material:
5-1.1 Equipment should be de-energized for all inspections, tests, repairs, and other servicing unless provisions are made to allow maintenance to be performed safely on energized equipment.
5-1.1.1 Many maintenance tasks require equipment to be shut down and de-energized for effective results.
5-1.1.2 Other maintenance tasks might specifically require or permit equipment to be energized and in service while the tasks are performed. Examples include taking transformer oil samples and observing and recording operating temperatures, load conditions, corona, noise, or lamp output.
5-1.1.3 Coordinating maintenance with planned production outages and providing system flexibility such as by duplication of equipment and processes are two means to avoid major disruptions of operations.
Section 5-6 (Equipment Cleaning) now includes new wording on the removal of contamination and loose items:
5-6.1 General. Various methods for cleaning are available, and the method used will depend on the kind of contamination to be removed and whether or not the apparatus is to be returned to use immediately.
5-6.2.2 To remove loose dust, dirt, and particles, suction cleaning methods should be used. Blowing out with compressed air is likely to spread contamination and damage insulation.
Section 5-7 (Special Handling and Disposal Considerations) is new to Chapter 5 and covers handling and disposing of certain electrical equipment, components, and materials. It covers items such as asbestos, PCBs, lead, mineral oil, tetrachlorethylene, thrichloroethane, mercury vapor and phosphor coatings, radioactive materials, and other harmful materials. It's a must-read for preventing fines imposed by the EPA because of unlawful use and disposal activities.
Chapter 6 (Substations and Switchgear Assemblies). This chapter is rewritten to include Section 6-8.4 (Stationary Batteries and Battery Chargers), which provides guidelines to ensuring proper battery maintenance. Special emphasis is on the critical maintenance function. Section 6-8.4 includes detailed information on general stationary batteries, including lead-acid and nickel cadmium types, as well as battery chargers. The authors also address maintenance programs as well as guidelines for safety, visual inspection and associated servicing, mechanical and miscellaneous investigation, and battery test and measurement.
Important points under Guide for Visual Inspections and Associated Servicing include:
Checking jars and covers for cracks and structural damage;
Examining interconnection cables, cell connectors, and other conductors for wear, contamination, corrosion, and discoloration;
Indications that excessive water consumption may be a sign of overcharging; and
High ambient temperatures reduce cell life.
Under Mechanical and Miscellaneous Investigation, important points include:
Checking terminal connectors, battery posts, and cable ends, and removing all corrosion and dirt; and
Indication that vibration reduces battery life. Battery Test and Measurement Guidelines suggests you:
Measure and record pilot cell voltage, specific gravity, and electrolyte temperature monthly, and
Perform a capacity test within the first two years of installation, and every three to five years thereafter, depending on load reliability requirements and environmental condition of the installation.
Chapter 9 (Motor Control Equipment). The authors thoroughly rewrote this chapter because motor technology changed significantly since the original chapter's writing. Also, safety procedures such as lockout/tagout expanded.
This chapter highlights:
Enclosures-cleaning and care in various environments and internal inspection of enclosures-what to look for, and interpreting existing conditions to locate sources of problems or potential troubles.
Inspection for loose connections, conductors, or components, including bus bars, terminals, grounding or bonding, stabs, and aluminum connections.
In addition, the standard gives maintenance procedures for various environments, vibration, power and control wiring, and insulators. It also covers recommended maintenance practices for disconnects, contactors, contacts and arc chutes, fuses, solenoids, relays, control circuitry, and protective devices.
Chapter 10 (Electronic Equipment). This chapter now reflects the extensive use of electronic equipment integrated with or replacing electrical or electromechanical equipment. It lists each phase of preventive maintenance, including inspection, cleaning, adjustments, testing, and servicing.
Section 10-2 (Reasons for Maintenance) suggests the following:
Protect equipment from adverse effects of heat, dust, moisture, and other contaminants; Maintain top reliability and minimize costly downtime;
Prolong the useful life of the equipment; and
Recognize incipient problems and take corrective action.
Section 10-3.1 explains the dangers of discharging capacitors, pointing out that capacitors with high stored energy can be lethal. The authors suggest discharging a capacitor through a resistor, followed by a direct short circuit to ground.
Chapter 11 (Molded Case Circuit Breaker Power Panels). Section 11-11 (Mechanical Mechanism Exercise) now emphasizes the importance of manual operation of circuit breakers while clearing up a misconception on their testing:
Devices with moving parts require periodic checkups. A molded-case circuit breaker is no exception. It is not unusual for a molded-case circuit breaker to be in service for extended periods and never be called on to perform its overload- or short-circuit-tripping functions. Manual operation of the circuit breaker will help keep the contact clean, but does not exercise the tripping mechanism. Although manual operations will exercise the breaker mechanism, none of the mechanical linkages in the tripping mechanisms will be moved with this exercise. Some circuit breakers have push-to-trip buttons that should be manually operated in order to exercise the tripping mechanism linkages.
Chapter 12 (Ground Fault Protection). Several sections are revised for better understanding of testing of GFCIs. Specifically highlighted are integral test button testing, separate test instruments, and record keeping.
Chapter 13 (Fuses). This chapter is a must-read because it recognizes new fuse types and current maintenance practices. It will help you select fuses, along with inspecting and replacing them.
The text includes safety rules, with reference to NFPA 70E-1995, Standard for Electrical Safety Requirements for Employee Workplaces. General types are defined as 0A to 600A and high-voltage power fuses to correlate with NEC. Classes of fuses in the 0A to 600A range are defined as to size and application. For example, Section 13-1.4.1 (Type) points out Class H, K, and R are the same physical size; however, special rejection style fuseholders will accept only Class R fuses. Class RK1 fuses are also more current-limiting than class RK5 fuses. The former is recommended to upgrade older distribution systems.
Discussed are interrupting ratings, time delay, and current limitation, along with special fuses. Section 13-2 (High-Voltage Power Fuses) details installing and removing fuses, along with their inspection and cleaning. Included are vented-expulsion fuses.
Chapter 15 (Lighting). Several updated sections cover lighting maintenance. Typical concerns are lumen depreciation, new lamp and fixture cleaning procedures, and considerations that relate to the Energy Policy Act of 1992. There's even information on relamping,
A typical example of the rewrite is Section 15-5.1 (Fluorescent lamps). It's rewritten to track the NEC. Except as identified by the NEC, all fluorescent lamp ballasts on fixtures installed indoors must contain integral thermal protection and be marked "Class P." The section also points out that intermittent lighting (blinking) of fluorescent lamps shortens lamp life and can damage ballasts.
Chapter 18 (Testing and Test Methods). This chapter is one of the largest in the document. Extensive changes in Section 18-16 (Infrared Inspection) covering infrared testing point out that when performing infrared testing, you should open equipment enclosures for a direct view of the components whenever possible. When opening is not possible, such as in some busway systems, you have to account for the fact that internal temperatures can be higher than surface temperatures. Plastic and glass covers in electrical enclosures are not transparent to infrared radiation. Also, you should use appropriate report forms. Provided are NETA (interNational Electrical Testing Assn.) specifications for temperature benchmarks.
Chapter 24 (Power Quality). This chapter is extensively revised throughout, and new material is added to keep up with latest technological advances. The chapter underwent extensive editorial changes and rearrangement to ease understanding.
One new section (Section 24-1.6) defines power quality disturbances as:
Harmonics imposed on the fundamental sine wave;
Voltage transients;
Voltage sags and swells;
Long duration undervoltage and sustained voltage interruptions;
Unbalanced voltages and single phasing (partial interruption);
Inadvertent/inadequate grounding;
Electrical noise; and
Interharmonics.
Figures show these power system disturbances. The standard discusses and/or illustrates, in detail, each of the above disturbances to help you understand them. For example, it defines the word "transients" (formerly referred to as surges, spikes or impulses) as: "...very short duration, high amplitude excursions outside of the limits of the normal voltage and current waveform. Waveshapes of the excursions are usually unidirectional pulses or decaying amplitude, high-frequency oscillations. Durations range from fractions of a microsecond to milliseconds, and the maximum duration is in the order of one half-cycle of the power frequency. Instantaneous amplitudes of voltage transients can reach thousands of volts."
Problems created by harmonics are listed in Section 24-2.2.1 as:
Excessive neutral current;
Overheating of transformers, motors, generators, solenoid coils, and lighting ballasts;
Nuisance operation of protective devices;
Unexplained blowing of fuses on power-factor correction capacitors;
Unusual audible noise in electrical switchgear;
Voltage and current waveform distortion that results in misoperation or failure of solid-state equipment;
Audible noise interference on telephone circuits;
Loss of data on computer systems;
Failure of UPS systems to properly transfer; and
Shaft voltages and currents in electric motors causing bearing failure, if the bearings are not insulated.
An excerpt from Section 24-2.2.8 states:
Computers and other computer-type equipment such as programmable logic controllers (PLCs) are very susceptible to harmonic-distorted waveforms, and the possibility of harmonics should be investigated on circuits serving such equipment where neutral-to-ground voltages in excess of 2 volts are measured.
Causes of harmonic distortion are discussed in Section 24-2.3. It explains:
The most significant contributor to harmonics is electronic equipment, especially equipment that utilizes a switching-mode power supply. The wave-chopping characteristic operation of thyristors, silicon-controlled rectifiers, transistors, and diodes develops current waveforms that do not conform to the applied voltage waveform, and therefore develops harmonics. Included among electronic equipment that is rich in harmonic generation are welders, battery chargers, rectifiers, ac and dc adjustable-speed motor drives, electronic lighting ballasts, computers, printers, reproducing machines, and programmable logic controllers.
Section 24-2-5 (Recommended Solutions to Harmonic Problems) includes:
Derating of existing equipment;
Replacement of existing equipment with higher rated equipment;
Use of delta-wye or delta-delta connected transformers;
Use of equipment specifically rated for harmonic circuits:
Better selection and application of protective and metering devices;
Use of rms-sensing-protective devices;
Balancing of single-phase loads on three-phase systems;
Use of three-phase rectifiers instead of single-phase rectifiers;
Relocating power-factor improvement capacitors;
Shielding of conductors and electronic equipment;
Isolation of harmonic-sensitive loads; and
Use of filters to block or shunt off harmonics. (Several additional recommended solutions are listed).
Section 24-3.4 (Transient Monitoring) explains where and how to connect monitoring equipment and provides solutions to transient problems.
New Section 24-4.3 (Voltage Sags and Swells) explains why a utility fault usually creates a more severe sag than a motor start because it will last until the fault is cleared or removed.
New Section 24-5.1.1 (Electric Utilities) includes the following:
Electric utilities may be required by their regulatory commissions to maintain service voltages within prescribed limits for the various types of service. Plant electrical people should be aware of any required service voltage limits for their type of service. The utility generally works with the customer to assure that the service voltage remains within the required limitations or within their standard design limits, where there are no required limitations.
Section 24-6 (Unbalanced Voltages and Single-Phasing) includes definition, causes, symptoms, motor operation under single phasing, testing, and solutions for unbalanced voltages.
Section 24-7 (Grounding and Bonding) clearly defines numerous key words and phrases, such as "multipoint grounding," "separately derived system," and "single point grounding." Meticulously presented are the benefits derived from proper grounding as well as problems resulting from improper grounding.
Section 24-8 (Noise in Electrical Systems) includes definitions for electrical noise terms like "common mode noise," "transverse mode noise," and "interference" (both EMI and RFI). Also discussed in detail are causes, symptoms, problems, testing and solutions.