Teaching an old dog new (electrical) tricks

There’s a better way to approach electrical problems than using a digital multimeter.


There’s a better way to approach electrical problems than using a digital multimeter. Use a non-contact tool, first. It’s safer and, in the end, faster. A non-contact tool can be a voltage detector, an infrared thermometer or a thermal imager.


If you’re working on a “dead” circuit, it’s always wise to quickly test it first with a non-contact voltage tester and verify that power is really disconnected. Sounds obvious, but you don’t have to look far to uncover too many accidents that could have been avoided.


If you’re troubleshooting a live electrical problem, chances are high that the cause of your problem will have a tell-tale heat signature associated with it. Take a minute to scan the electrical equipment with an infrared thermometer or a thermal imager. Even if you see nothing abnormal, you’ve still learned something: what’s not wrong. If you do see an abnormally hot or cool spot, you’ve determined where to start your investigation. And in the process of thermal inspection, you’ll often notice other developing issues with the panel/motor/control that you can address preemptively.


In any live electrical measurement situation, the technician must still wear appropriate PPE. The benefit is that since no direct contact is necessary with infrared and thermal measurement, the risk of accidental arc flash is lower.


When choosing between an infrared thermometer and a thermal imager, the choice is situational. Most technicians now carry a small infrared thermometer in their pocket for on-the-go checks. However, the infrared thermometer gives you only a “spot” temperature reading. If you know what you’re looking for, infrared may be enough. But if you’re hunting an elusive problem, a full thermal map of the entire unit is more effective.


More about thermal imaging

Thermal imagers detect and measure surface temperature differences and assign colors based on temperature. Rather than seeing light, thermal imagers create pictures of heat. They measure infrared energy and convert the data to images corresponding to the temperature.


The biggest trick with using a thermal imager effectively is understanding emissivity. Emissivity describes how well an object’s surface emits IR energy, or heat. This affects how well a thermal imager can accurately measure the object’s surface temperature.


Most painted objects, ceramic, rubber and most electrical tape and conductor insulation, have high emissivities. This makes them ideal for thermal imaging. Aluminum bus, however, is very reflective, and so are copper and some kinds of stainless steel.


The good news is that most thermal imaging performed for electrical inspection purposes is a comparative, or qualitative, process. You don’t usually need a specific temperature measurement. Instead, look for a spot that is hotter than similar equipment under the same load conditions, spots that you do not expect.


Commonly inspected components with thermal imagers include:


  • Three-phase power distribution and switchgear
  • Fuse boxes
  • Cables and connections
  • Relays and switches
  • Insulators
  • Capacitors
  • Circuit breakers
  • Electric motors
  • Motor controllers
  • Transformers
  • Battery banks
  • Substations.

Typical reasons for temperature hotspots or deviations include:


  • Unbalanced loads
  • Harmonics (third harmonic current in neutral)
  • Overloaded systems/excessive current
  • Loose or corroded connections* increasing resistance in the circuit (typically one side of components heats up)
  • Insulation failure
  • Component failure
  • Wiring mistakes
  • Underspecified components (like fuses, would heat up on both sides of the fuse).

* Note: Not all electrical problems discovered by thermal imaging are high-resistance connections. Follow and analyze the thermal pattern of the conductors and other components to assess other possibilities.


Scope of possibilities


The possible applications for thermal imaging are broad but not endless. Constraints and cautions include:


  • Equipment must be operating (ideally at the highest possible load, minimum 40%)
  • Direct view: Open enclosure doors, when possible. You cannot see through enclosure doors
  • Understand present and future loading conditions
  • Only qualified persons should access live electrical equipment
  • Avoid working in direct sunshine, as the sun’s heat can mask some problems
  • Be aware of air convection and cooling, and account for windy conditions when outside
  • You can detect only surface temperatures
  • Be aware of low emissivity materials
  • Look for both hot and cold abnormalities, since sometimes “cold” also indicates a problem
  • Check all connections and points of electrical contact
  • Compare all phases to each other, and compare items under similar loads. They should have similar thermal signatures when operating properly.

What happens next?


Thermal imagers work best in the hands of skilled technicians who understand the equipment in question. A hot phase could indicate an unbalance, overload, bad connections and so on. If the problem isn’t immediately identifiable as a bad connection, use a properly-rated digital multimeter or power quality analyzer to trace the problem to the root.


As with any measurement technology, there is no substitute for proper training and experience. Although thermal imaging is a powerful tool, and it has become even easier-to-use and more affordable in recent years, it does require some basic knowledge. Invest in proper thermal training to build your inspection skills, increase electrical measurement safety and improve problem-solving efficiency well into the future.




Different materials emit infrared energy in different ways. Every object and material has a specific emissivity rated on a scale of 0 to 1.0. A thermal imager can accurately calculate the surface temperature of an object only if the emissivity of the material is relatively high (close to 1.0), and/or the emissivity level on the imager is set close to the emissivity of the object. 




Author Information
Michael Stuart manages thermal imagers for Fluke Corp. He has trained with the Snell Group and has spent extensive field time documenting electrical and industrial thermal applications. Previously, Stuart mastered the somewhat arcane knowledge field of insulation resistance test and managed electrical testers of all types for Fluke Corp. He can be reached at michael.stuart@fluke.com.


Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
October 2018
Tools vs. sensors, functional safety, compressor rental, an operational network of maintenance and safety
September 2018
2018 Engineering Leaders under 40, Women in Engineering, Six ways to reduce waste in manufacturing, and Four robot implementation challenges.
GAMS preview, 2018 Mid-Year Report, EAM and Safety
October 2018
2018 Product of the Year; Subsurface data methodologies; Digital twins; Well lifecycle data
August 2018
SCADA standardization, capital expenditures, data-driven drilling and execution
June 2018
Machine learning, produced water benefits, programming cavity pumps
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
October 2018
Complex upgrades for system integrators; Process control safety and compliance
September 2018
Effective process analytics; Four reasons why LTE networks are not IIoT ready

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Material Handling
This digital report explains how everything from conveyors and robots to automatic picking systems and digital orders have evolved to keep pace with the speed of change in the supply chain.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Design of Safe and Reliable Hydraulic Systems for Subsea Applications
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
click me