Why Can’t Thermal Imaging Cameras See Through Electrical Panel Doors?
“The last thermographer didn’t need the doors open — why do you?”
This is a question thermographers often hear when arriving onsite. It’s understandable — no one likes to stop production, unlock panels, or coordinate permits unless absolutely necessary. But the truth is simple: thermal imaging cameras cannot see through solid electrical panel doors, glass, or most other common materials.
Let’s break it down.
The Science Behind Thermal Imaging
Infrared (IR) thermography works by detecting heat emitted as infrared radiation from an object’s surface. Thermal cameras convert this radiation into an image that shows temperature differences — a very powerful tool for condition monitoring. But here’s the catch:
IR cameras cannot see “through” objects.
They only detect the temperature of the surface they’re aimed at.
That means if you're pointing a thermal camera at a metal panel door, all you’ll capture is the temperature of the outside of the door — not what’s going on inside with your busbars, terminals, or fuses.
What About Glass or Windows?
Another common misconception is that thermal cameras can see through glass or building windows, similar to how our eyes do. In reality:
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Ordinary glass blocks infrared radiation.
Even though it’s transparent to visible light, it's opaque to IR wavelengths used in thermography. - What you see is a reflection, not a true thermal reading of what’s behind the glass. In fact, glass can reflect your own body heat or surroundings, leading to misleading or useless results.
IR Windows: A Practical Workaround
In environments where regular panel inspections are needed and downtime is costly, IR windows offer a helpful solution. These are specially designed ports or "windows" made from materials like germanium or zinc selenide, which allow infrared radiation to pass through.
Benefits:
- Enable safe, closed-panel thermography
- Reduce the need for PPE or electrical shutdowns
- Speed up inspections and data collection
However, they have limitations:
- Field of view is restricted: You only see what the IR window allows.
- Installation costs: High-quality IR windows can be expensive.
- Potential for missed faults: If the fault lies outside the viewing area, it may go undetected.
- Surface condition: If the inside components are obscured by dust or insulating material, thermal readings may still be unreliable.
Why Opening the Panel Matters
To get meaningful, reliable thermographic results, thermographers need direct line-of-sight to the components inside an electrical panel. That often means:
- Opening the panel door (with proper safety precautions and permits)
- Ensuring clear access to internal busbars, lugs, circuit breakers, etc.
- Removing obstructions like insulation or plastic covers
Without doing so, the inspection becomes an exercise in guesswork, potentially missing serious faults or creating a false sense of security.
Conclusion
While technology like IR windows can assist in specific cases, there’s no substitute for proper access during a thermal inspection. A qualified thermographer will always prioritize both safety and accuracy — and that starts with knowing what the camera can and can’t see.
So next time someone asks why the door needs to be opened, you’ll have the answer:
Because thermal cameras can’t see through metal, glass, or wishful thinking.