How do Infrared Hot Spots Magically Appear?
- Jeff Kershner
- Feb 23
- 3 min read
“You found a hotspot caused by a loose wire in my electrical equipment? I just tightened that wire! And how did the screw come loose?”
Sometimes, an Infrared (IR) Thermography Electrical Safety Inspection report shows “hotspots” in equipment that appears to be working just fine.
However, even if a screw is tightened perfectly on day one, there are forces that work to loosen it over time, in very small increments, even despite regular maintenance. Screws in electrical equipment don’t just "fall out"; they are typically pushed loose by invisible physical forces until the tipping point.
Below, we break down the forces leading to imperceptible, incremental changes—and eventually—equipment failure.
Mechanical Failure: How Screws Come Loose
Three primary forces work to loosen a perfectly tightened screw over time.
Thermal Cycling (The "Breathing" Effect):
When current flows through a wire, it heats up. When the current stops, it cools down. Metals expand when hot and contract when cold. Crucially, different metals expand at different rates (e.g., an aluminum wire expands more than a steel screw).
The Ratchet Effect: When the equipment gets hot, the expanding wire pushes hard against the screw. If it pushes too hard, it can permanently deform the wire (squishing it) or stretch the screw. When the system cools down, the materials shrink back, but because of that deformation, a microscopic gap opens up. The connection is now looser than before.
Creep (Cold Flow):
Softer metals like copper and aluminum behave somewhat like very stiff clay. Under the constant pressure of a tightened screw, the metal can slowly "flow" away from the pressure point over months or years. As the metal thins out under the screw head, the tension holding the connection together disappears.
Vibration:
In industrial settings or equipment near motors (transformers, HVAC), constant subtle vibration causes micro-slippage. These tiny movements can slowly rotate a screw backward, millimeter by millimeter, especially if the initial spring tension has already been reduced by creep or thermal cycling.
Electrical Failure: The Creation of a Hot Spot
Once the screw is loose, the connection creates a "Hot Spot" through a process called Thermal Runaway.
Increased Contact Resistance
A tight connection allows electricity to flow through thousands of microscopic contact points. A loose connection forces that same amount of electricity to squeeze through only a few tiny points of contact.
The Physics: This bottleneck increases electrical resistance. According to Joule’s Law (P = I2R), heat generation is proportional to resistance.
Result: The connection point becomes significantly hotter than the surrounding wire.
Oxidation
Heat acts as a catalyst for chemical reactions. As the loose connection gets hot, it reacts with oxygen in the air to form oxides (like copper oxide or aluminum oxide) on the surface of the metal. Sometimes, this is visible in the form of rust, but more often you would not notice it with the naked eye.
Most metal oxides are electrical insulators (they don't conduct electricity well).
This oxide layer adds more resistance to the connection, which generates more heat, which creates more oxide.
Arcing and Fire
Eventually, the resistance becomes so high that the connection acts like a heating element.
Glowing: The metal can glow cherry-red.
Arcing: If the gap becomes wide enough, electricity may jump (arc) across it. Arcs are incredibly hot and can instantly melt the screw, the wire insulation, and the plastic housing, igniting a fire. Just to be clear: “arc” is not an “arc flash”. With arcing, the electricity is jumping a gap within the same conducting path and not to another phase or ground (which would initiate an arc flash).
Prevent Hot Spots With Regular IR Electrical Safety Inspections
Periodic infrared inspections as prescribed by NFPA 70B (which since 2023 mandates infrared scans at least every 12 months for most equipment) will catch hotspots before they cause downtime. Taking action after discovering a hotspot will allow you to schedule downtime instead of your equipment scheduling it for you.
Following our 2025 acquisition of Monroe Infrared, Guidant Power now performs infrared inspections across electrical systems, buildings and roofs nationwide.
