Infrared Windows for Switchgear and IR Viewing Window Installation

What an IR Viewing Window Does

An IR viewing window is a permanent port fitted into a switchgear, MCC, transformer or bus enclosure that lets a thermographer image the connections inside without removing a cover. The enclosure stays closed and latched while the scan is taken, and a protective cover closes the port between scans.

Ordinary glass and acrylic block most of the infrared energy a thermal imager reads, so a window uses an optic chosen to pass that energy: a crystal lens, an infrared-transmitting polymer, or a fine metal grille in some designs. Each type passes a known share of infrared, and the thermographer enters that transmission value into the imager so temperature readings stay meaningful.

Windows are usually round ports of a few standard sizes, mounted through a cut-out in the door or cover panel and bolted from the inside. Positions are chosen so the field of view takes in the cable terminations, bus joints or breaker connections that matter most. Done well, one window can replace the routine removal of a heavy bolted cover every time the equipment is scanned.

If you are still deciding whether to scan at all, start with infrared electrical thermography. This page is for owners who already scan, or plan to, and want to do it through closed doors.

What Infrared Windows Change, and What They Do Not

Infrared windows change how the scan is done: covers stay on, so the routine thermal survey no longer requires exposing energized parts. They do not change the hazard inside the equipment, and they do not replace your arc flash study, labels or PPE rules for any task that still opens the gear.

Windows also change the paperwork. Because the door stays shut, the scan itself no longer counts as a task that exposes energized parts, which simplifies the permit and PPE planning around routine surveys. That only holds while the window cover is the only thing opened; the moment a door or cover comes off, the full risk assessment applies again.

The main benefit is exposure: fewer occasions on which a worker stands in front of open, energized equipment. A second benefit is time; routine scans become quicker once covers no longer need to come off. The trade-off is line of sight. A window shows only what it was positioned to show, so placement planning is the most important part of the job. For the hazard itself, see our arc flash study service.

Where IR Windows for Switchgear Make the Most Sense

Infrared windows for switchgear make the most sense where covers are bolted, where the arc flash rating for opening the gear is high, and where the equipment is scanned often enough that the one-time installation pays back in safer, faster scans. They make little sense on equipment that is easy and low-risk to open.

Equipment on a six-month scan cycle is a natural candidate. NFPA 70B (2023 edition) sets that interval for thermography on Condition 3 equipment, which includes critical gear and harsh environments, so a main switchboard scanned twice a year would otherwise have its covers off twice a year, every year, for an infrared inspection that ANSI/NETA MTS lists among its maintenance tests. Plants running regular industrial thermography surveys often add windows to the gear that is hardest to open.

Certified Equipment and the Approval Route in Ontario

Fitting an IR window means cutting into a certified enclosure, and in Ontario that is a modification to certified equipment that needs an approved route before any cutting starts. We confirm that route with you, the equipment manufacturer and the Electrical Safety Authority (ESA) at the planning stage.

ESA expects changes to certified equipment to be carried out by the company that built it, or by agents working on its behalf. Depending on the gear, the practical paths include:

• Manufacturer-supplied parts. Some switchgear makers offer replacement doors or covers with windows already fitted, or approve specific windows for their product.
• Manufacturer approval for field installation. Written approval for a particular window, size and location, which we follow exactly.
• A field evaluation or other route ESA accepts, where the original manufacturer no longer supports the gear.

Arc-resistant switchgear needs particular care. Its rating depends on the enclosure holding together and venting as designed, so any opening must be approved by the manufacturer for that line-up. We will not cut an arc-resistant enclosure on our own judgement.

The window itself should carry certification and ratings suited to the enclosure it goes into, including its environmental rating, so the enclosure keeps its protection against dust and moisture. These checks are part of our quote, so you know the route before you commit.

Planning Window Locations for Full Line of Sight

Window placement decides what you will be able to see for the life of the equipment, so we plan it from the inside: which connections carry load, where heat would show first, and what blocks the view. A window in the wrong spot is just a hole with a lid.

1. Target list. From drawings and an internal inspection during an outage, we list the targets: incoming cable lugs, bus splices, breaker line and load connections, CT connections and outgoing terminations.
2. Field of view. For each target we check distance, angle and obstructions such as barriers, shutters and cable bundles. Sometimes two smaller windows give a better view than one large one.
3. Clearances. Windows must clear internal live parts, door hinges, latches, nameplates and labels, and must not weaken structural members.
4. Layout drawing. We produce a marked-up layout showing each window, its ID and what it is meant to see, for your approval and for the manufacturer where their approval is needed.
5. Labelling. Each window gets an ID label that matches the scan report, so future thermographers know exactly what each port covers.

Where some targets simply cannot be seen through any practical window, we say so. Those points stay on a list for inspection during planned outages, often as part of switchgear maintenance.

IR Viewing Window Installation Day: Outage, Cut-Out and Baseline

IR viewing window installation needs one planned outage per piece of equipment, because cutting into an enclosure is never done with the gear energized. After installation the equipment is restored and given a first baseline scan through the new windows.

• Isolation. Supply to the gear is isolated, then locks and tags go on in line with Ontario Regulation 851 and our written procedures, coordinated with your own lockout program, and absence of voltage is verified before work begins.
• Debris control. Doors or covers are removed and taken to a work area where possible. Where the cut has to be made in place, the interior is shielded so no metal chips or dust reach bus or insulators.
• Cut-out and mounting. Holes are cut to the window maker's template, deburred, and the windows fitted and tightened to their stated torque, with gaskets in place.
• Inspection and restore. The enclosure is inspected inside for debris, covers are refitted, and the equipment is returned to service following your switching procedure.
• Baseline scan. Once the equipment carries normal load, we image through each window, confirm the field of view matches the plan, and record baseline readings.

Where windows go into new gear or a replacement lineup, the work is checked as part of acceptance testing to ANSI/NETA ATS (2025 edition) before energization, and on a full new installation, ANSI/NETA ECS (2024 edition) covers commissioning of the whole system at start-up. We often combine window installation with other outage work, such as cleaning, bolt torque verification and electrical tests, so one shutdown covers several tasks. As a licensed contractor (ESA/ECRA #7014042), we file any notification the work requires.

How Thermographers Scan Through an IR Window

Scanning through an IR window requires the thermographer to correct for the optic's transmission, keep a consistent viewing angle, and watch for reflections, so the readings can be compared to scans done with covers off and to previous scans through the same window. Our Level II certified thermographers record these settings for every window.

The window's transmission value, the emissivity of the target surface and the distance are entered into the imager before each image. Viewing straight on gives the most reliable reading; steep angles reduce what the window passes and can create reflections from the optic itself. Visible-light photos taken through the window, where the design allows, help confirm what each thermogram shows.

Because the same window gives the same view every time, trending is easier than with covers off. That consistency is one reason windows are popular in predictive maintenance programs where small changes between scans matter.

Caring for Windows and Keeping Records

IR windows need little care, but they do need some: keep the covers closed, keep the optic clean and undamaged, and keep each window's ID and transmission value in your maintenance records. A scratched or dirty optic quietly reduces the accuracy of every future scan.

• Check covers and gaskets at each scan, and replace damaged covers promptly.
• Clean optics only as the window maker directs; some materials are sensitive to moisture or solvents.
• Keep a register of windows with location, ID, size, optic type and transmission value.
• Note any window whose view has been blocked by later changes inside the gear, such as added cables or barriers.

We add the window register to your electrical preventive maintenance records, so window checks happen automatically during each visit.