The importance of inspecting small electrical devices

The benefits of using infrared thermography as a predictive maintenance (PdM) tool for electrical applications are well known. Most PdM programs in industrial facilities have routes and frequencies for inspecting their critical electrical assets. Substation equipment, service main switchgear and MCCs are commonly inspected with frequencies as high as monthly in some instances. Yet for every large distribution apparatus scanned with regularity, any number of 208Y/120 panels, control panels and other ‘small’ devices are often overlooked. This article explores the benefit of including previously uninspected ‘small’ electrical system components to routes that have previously been occupied by switchgear and MCCs.

Many large-scale processes are either controlled or monitored by human machine interface (HMI) devices or control systems are powered by 120 VAC and lower supplies. Small panels in offices or control rooms often power servers or desktop computers that annunciate processes or monitor critical data within a process. The amperage rating of a device or enclosure no longer correlates to criticality, so it is time we started sweating the ‘small stuff’.

The IR field has seen quite a few changes over the years. Camera innovation would be chief among those. Thermography was once upon a time a much more tedious and cumbersome endeavour than it is today.

As an instructor of IR, I often have students in the level-one course who complain about the size and weight of their cameras. That all ceases after I show photos of older equipment such as the Inframetrics 740 rig from back in the early 1980s. Believe it or not, this was once considered ‘man-portable’.

Well thank goodness for technology. Today’s cameras are smaller, less expensive and have increased portability in comparison to what we lugged around in the ‘old days’. Every camera on the market today has onboard memory, which is a far cry from the ‘Polaroid camera attachment’ days and even a huge improvement over carrying a video recorder attached to your imager. These technological advancements mean we can get more done in less time and at a reduced cost. But are we taking full advantage of these improvements? As a service provider, my personal experience has been that as inspection costs decrease, the savings are not passed on to increase the number of assets within the scope or the frequency of inspection. The opposite is often true with the scope of an inspection decreasing, leaving small equipment out in the cold while switchgear equipment and large distribution devices remain on inspection lists.

Of course, facility switchgear equipment is quite critical as it is the heart of the electrical distribution system. Obviously, industrial equipment requires its operating voltage in order to perform, hence the inspection of distribution devices that feed process equipment. But why leave off the circuits feeding the process control or HMI devices like touch screens and control panels? If the switchboard feeder breaker for your conveyor line never goes down, but the programmable logic controller controlling it fails catastrophically due to a heat-related failure in its distribution path, what has been saved?

Anyone with knowledge of thermography as applicable to electrical apparatus inspections understands how we find anomalies. Increased contact resistance in an electrical connection causes heating that increases as the square of the applied current. One common misconception is that the resistance within the connection point has to be very high in order to cause heating. This is untrue.

Another common misconception is that lower power devices do not carry enough current to be susceptible to heat-related failure. This is also untrue. While abnormal heating is a product of current squared times the resistance (I2R), and electrical devices are rated according to their ability to accommodate the flow of current, lower current rated devices can also experience heat-related failure.

Here is an example: Let’s assume that in the thermal image of a 14 AWG control wire, which is rated for between 25 and 35 A depending on which particular wire type is used, the conductor is only showing abnormal heat at the connection point, not on the entire conductor. This would appear to indicate that the conductor itself is not overloaded and that the heat present is due only to the current flowing through the high resistance connection point. Note the apparent temperature of the anomaly by comparing the colour to the temperature scale. An apparent load of significantly less than 30 A is producing over 149°C. Also important to note is that the control circuit was for an industrial boiler and if it had failed the boiler would shut down, halting the process of this facility.

What about voltage levels? Among the common criteria used to determine criticality of electrical apparatus for inspection is the voltage class or rating of the device. Again, abnormal heating in an electrical connection is a product of current, not voltage. The voltage level of the device has no bearing on the potential for a heat-related failure. Control panels offer an excellent opportunity to maximise the benefit of thermography as a predictive technology, but sadly they are often overlooked. Contained within a typical control panel are transformers, fuse blocks, circuit breakers and a host of other electrical devices that are inspected in their larger forms inside of bigger devices. The control transformer inside a control panel operates exactly the same as the larger ones we inspect as part of the utility equipment. Just because they are smaller versions of what we normally would consider critical devices does not mean they should be inspected at a reduced frequency. Even small components like those mounted on DIN rail can have sufficient I2R in their connection points to experience heat-related failures.

For example, the 20 A circuit breakers inside a control panel have the same potential for failure as the 400 A ones in a distribution switchboard. Does the 20 A circuit breaker cost less to replace? Sure it does, but what impact on the overall process of the facility does it have? Can we reasonably expect that a circuit breaker could not experience the same degree of abnormal heating because it is in a 120 VAC panel as opposed to a 480 VAC distribution board? What if this circuit breaker is the one feeding the production computer terminal in an office space? Are you sweating the small stuff yet?

Service main switches are routinely inspected, but what about the 20 A service disconnect for the control panel? Downtime is downtime, no matter the cause. We need to be inspecting these devices inside of control panels.

As reliability professionals within a facility, your input to the routes and frequencies of asset inspections is crucial in bringing about a change. The assessment of criticality for any asset within a particular route needs to consider the impact of failure of devices previously believed to be unimportant due to its voltage class or current rating. As a service provider for client companies, your task is to educate your customers on the importance of including these small devices in their routes. Often a service provider only sees their customers once or twice a year and they are almost always pushed to get as much out of their annual visit as they can and to cut time out of the inspection process to stay competitive in their pricing. It is often an uphill battle to make changes - we know that from the history of IR thermography itself. But it can happen and you can make it happen if you start sweating the small stuff.

*Dave Sirmans joined The Snell Group in 2008 as Operations Manager. He is responsible for managing and coordinating The Snell Group’s field service operations and overseeing the company’s team of technicians that offer infrared thermography, motor circuit analysis and ultrasound testing services at various locations throughout the United States. Also, Dave is responsible for developing curriculum for The Snell Group’s Knowledge Products and is a trainer for both IR Thermography and Motor Circuit Analysis courses. Dave is also a Certified Maintenance & Reliability Professional (CMRP). Dave instructs Level I, Level II and IR for Weatherization and Energy Audits classes for infrared, as well as both Energized and De-Energized Motor and Motor Circuit Analysis courses.

The Snell Group
www.thesnellgroup.com