Yes, you read that correctly. When you attended Level I and Electrical IR was discussed, we specifically discuss the need for current flow to inspect. The NFPA-70B, Recommended Practice for Electrical Equipment Maintenance, suggests 40% load as a minimum to ensure adequate heating to reveal thermal anomalies. We stand by that, and further suggest that you work with the heaviest load possible to ensure detection. So why are we discussing de-energized scanning?

Sometimes there are reasons that electrical equipment cannot be rendered exposed for inspection; panel covers that can’t be removed, MCC buckets that can’t be opened or control panel doors unable to be opened. Perhaps there’s a mechanical interlock that can’t be overridden. Site or corporate policies regarding particular equipment, areas where access can’t be controlled. Whatever the case may be, sometimes you’re just not allowed to open it while it’s operating. The easiest answer is to skip it. You make a note that the customer doesn’t grant access and leave it be. Is that the best thing for equipment effectiveness? We all know that’s not following best practices.

Here’s the solution; de-energize and then open and inspect. Before we continue, there are some very important factors that must be considered. This type of approach takes significant coordination, approvals, supporting procedures etc.  Without these safety, product or equipment damage, lost production could occur. It is also possible that a coordination plan is required for equipment startup. So before this type of an approach is utilized, all of the above mentioned elements must be in place.

 Just as with other inspection methodologies, certain conditions must be met. While operating, the load still needs to have been above 40%, worse case loading if possible. Additionally, accessing the equipment must be accomplished fairly quickly after being turned off. As soon as de-energization occurs, current stops flowing, which as you should recall means that heat is no longer being generated. The heat that was being generated (both normal, inherent heating and the abnormal kind) will quickly dissipate through the combined effects of conduction, convective cooling and diffusion through the electrical components. So, you can’t take your time when taking this approach.

Will you get the same view as you would with an energized scan?  Absolutely not. The moment current stops the thermal profile changes. It is however much better than not scanning it at all. In addition, the opportunity will be there to perform a visual inspection, which often finds things you wouldn’t thermally. All in all, it’s a decent solution to inspect equipment to which you might not otherwise have access. IR windows often aren’t installed in some equipment, so de-energized scans might be your only option. While not ideal, they offer a glimpse and sometimes that’s all we need.