Build a Better Mousetrap: NFPA 70E 205.4 and Noncontact Diagnostic Methods

The 2024 edition of NFPA 70E 205.4, General Maintenance Requirements, states, “Electrical equipment shall be maintained in accordance with manufacturers’ instructions or industry consensus standards to reduce the risk associated with failure.” Informational Note No. 2 of this section provides more specific guidance with the very important sentence, “Noncontact diagnostic methods in addition to scheduled maintenance activities of electrical equipment can assist in the identification of electrical anomalies.”

Infrared thermography

Noncontact diagnostic methods such as infrared (IR) thermographic surveys can play a role as part of a predictive maintenance program for electrical power systems. During the thermographic survey, an?IR camera is used to detect heat and displays an image of the temperature distribution.

Over time, influences such as thermal expansion and contraction and electrical equipment vibration can cause terminations to become loose, which creates additional contact resistance and hot spots. Other causes may include internal arcing, unbalanced loading and similar factors. When current flows through an increased resistance, more heat is produced.

Most electrical components show an increase in temperature that can degrade electrical insulation. Infrared thermography can be used to identify these heat-related anomalies when there may be sufficient time for corrective action before a component fails, causing equipment damage, process disruption and possible safety hazards.

Years ago, one of my power quality projects identified a heating problem on one of the secondary conductors of a 1,500 kVA transformer. Due to the ampacity requirement, multiple conductors in parallel were run for each phase. Ideally, current should be evenly distributed in each conductor. However, the investigation revealed that one terminal was loose, increasing contact resistance. This resulted in uneven loading and an unusually hot termination. A simple solution—tightening the termination—just needed to be identified.

Electrical hazards

Equipment must be energized during the survey to obtain meaningful thermal data. NETA and NFPA 70B standards recommend that infrared scans be performed with a minimum of 40% load or at the highest normal load whenever possible. This means performing the survey in an electrically safe work condition is difficult.

Although opening the electrical equipment’s door can expose the thermographer to potential electrical hazards, NFPA 70E Table 130.5 lists the likelihood of occurrence of an arc flash incident as “No” for infrared thermography outside the restricted approach boundary. However, “No” does not apply for opening equipment covers and doors. When a door is opened, ask yourself if it was properly secured by the last person. On more than one occasion, I have been met with a surprise when a conductor that was pushed into the enclosure by the door sprung back when the door was opened.?

One option that may be used to reduce or eliminate the need to open the enclosure doors for IR scanning is to install infrared inspection windows in the equipment enclosure. This permits conducting the IR scan through the inspection window with the door closed, keeping the thermographer away from the electrical hazards. These windows must be carefully selected and installed to provide an optimal line of sight and minimize blind spots for the IR camera.

Continuous thermal monitoring

Long intervals between IR surveys (ANSI/NETA MTS-2019 Appendix B, Section 9 suggests 12-month intervals between surveys) can result in issues developing in the interim. To simultaneously address the snapshot issue and employee exposure to electrical hazards, a method known as continuous thermal monitoring (CTM) has been gaining acceptance. This method continuously monitors temperature in critical areas of equipment using sensors such as thermistors, thermocouples and resistance temperature detectors, fiber optic temperature sensors and IR sensors. CTM keeps workers isolated from electrical hazards and can provide a continual stream of data for transmittal, monitoring and analysis as part of a predictive maintenance program.?

A new IEEE working group is developing a standard that will be known as IEEE 2969, Guide for Continuous Thermal Monitoring of Switchgear and Motor Control Centers Below 52 kV, which is another indicator that using CTM is on an upward trajectory.?To “build a better mousetrap” generally means to invent the next great thing. As NFPA 70E continues to elevate electrical safety to new levels, the electrical industry continues to build better mousetraps.

This article was originally published in the July 2023 Edition of Electrical Contractor Magazine.