Electrochromic SmartGlass wiring through a load-bearing partition: why conduit placement breaks the uniform tint cycle in a Hennur retrofit

A two-storey residence in Hennur, completed last month, specified electrochromic dimming glass across a 4.2-metre library partition. The glass was commissioned to tint uniformly from clear to 65 per cent opacity on a single control loop. By handover, the tint pooled at the top third and edges, leaving the lower half noticeably lighter. The cause was not the glass, the transformer, or the relay placement. It was the path of the 4mm² power conduit routed through the load-bearing spine wall behind the partition, which created a thermal gradient and induced uneven voltage drop across the bus bars laminated into the film.

This is not a rare edge case. It is a coordination failure that repeats because architects and engineers rarely synchronise the electrical routing with the glass spec at the drawing stage. The conduit placement should be specified before the shop drawing is issued.

Why electrochromic film is sensitive to conduit routing

Electrochromic glass (sometimes called switchable glass or smart glass) works by applying a low-voltage electrical field across a film sandwiched between two panes. The field is distributed through bus bars — thin copper or silver conductors — that run along the edges and sometimes down the middle of the glass. When voltage is applied evenly, the tint is uniform. When voltage pools or drops unevenly, the tint becomes patchy.

The bus bars in a typical 1.8m × 2.4m panel operate at 24–48V DC, supplied through a transformer and relay. Current flows from the power source through the bus bars to complete the circuit. If the conduit carrying that power is routed close to the glass, it radiates heat. If the conduit is routed through a structural element behind the glass (as it often is in retrofit work), it can warm one side of the partition, causing the transformer or relay on that side to drift in output voltage. The bus bars on the warmer side of the glass receive slightly higher or lower voltage than the cooler side, and the tint responds accordingly.

The Hennur partition: what happened

The library partition was 100mm thick: 6mm toughened glass, 16mm air cavity, 6mm electrochromic-laminated glass, 10mm cavity, 6mm toughened backing. The load-bearing spine wall behind it was 230mm of reinforced concrete, finished with a 50mm cavity for services.

The electrical contractor routed the power conduit (4mm² two-core + earth in 16mm PVC) vertically through the spine wall, 150mm to the left of the partition's centreline. This was the standard practice: keep the conduit in the structural zone, away from the glazing line. But the conduit sat in the cavity, uninsulated, within 200mm of the back face of the electrochromic glass. During the monsoon humidity season (June to September in Bangalore), the air in that cavity became saturated, and the conduit began to radiate heat from the transformer load cycles. The temperature difference between the left and right sides of the partition reached 2–3°C during peak tinting cycles.

The transformer, mounted on the left side of the partition, drifted its output by approximately 1.2V across a 36V nominal supply. The bus bars on the left edge of the glass received 36V; the right edge received 34.8V. The tint response is non-linear: a 1.2V drop is the difference between 65 per cent opacity and 52 per cent. The top third, where the conduit's thermal influence was strongest, tinted darker; the bottom, cooler section remained lighter.

Conduit placement: the specification that prevents the problem

The fix was not to replace the glass. It was to relocate the conduit and insulate the transformer.

Routing options in a retrofit partition

When specifying electrochromic glass in a load-bearing partition retrofit, the electrical route must be nominated in the architectural drawing, not left to the contractor. The options are:

• Route the conduit vertically on the opposite side of the partition from the transformer (minimum 500mm separation from the glass face).
• Route the conduit horizontally above the partition, through the ceiling zone, and drop down to the relay on the far side.
• If conduit must pass through the structural cavity, encase it in 50mm rigid foam insulation and mount the transformer on a bracket at least 300mm away from the partition surface.
• Specify a larger transformer (next size up in VA rating) to reduce load-cycle heat output and stabilise voltage regulation.

In the Hennur case, the architect revised the RCP (reflected ceiling plan) to show the conduit running horizontally through the ceiling void, 1.2 metres above the partition. The transformer was relocated to a recessed box on the opposite wall, 2.8 metres away. A second conduit run, 6mm², was brought down to the relay mounted on the frame of the electrochromic panel itself. This separation ensured that no single thermal source could influence the voltage distribution across the bus bars.

The relocation added 180 rupees per metre to the electrical cost and required a site dimension check during framing. It took one day to revise and re-route. The alternative—replacing the glass—would have cost 85,000 rupees and caused a three-week delay.

Joint tolerance and voltage regulation

Electrochromic glass manufacturers specify a maximum voltage tolerance of ±2V across the panel width for uniform tint. Most transformers regulate to ±1V under normal conditions. But in a retrofit, where the conduit, relay, and glass are spread across multiple surfaces and cavities, the tolerance stack-up can exceed ±2V if the routing is not coordinated.

To stay within tolerance, the rule is simple: the power source (transformer and relay) should be mounted within 3 metres of the glass, on the same electrical loop, with the conduit routed in a thermally neutral zone (not in a cavity adjacent to the glass, not exposed to direct sunlight, not bundled with other high-load services). If the distance exceeds 3 metres, upgrade the conduit to the next size and specify a regulated DC supply instead of a standard transformer.

Retrofit coordination: what to spec before the shop drawing

For any retrofit project in Bangalore involving electrochromic or switchable privacy glass, the coordination checklist should include:

1. Electrical route: mark the conduit path on the RCP and section, with distances from the glass face and from the transformer.
2. Transformer location: specify a surface-mounted or recessed box, with mounting details, at least 300mm from the partition face.
3. Voltage regulation: confirm the transformer model and regulation spec (±1V minimum).
4. Thermal insulation: if the conduit must run within 200mm of the glass, specify foam insulation around the conduit.
5. Bus bar termination: confirm with the glass supplier that the relay mounting and bus bar connection points do not create a voltage drop greater than 0.5V per connection.
6. Site dimensions: measure the actual partition depth, cavity width, and structural element positions before finalising the electrical layout.

This coordination takes place in the design development phase, not on site. If the electrical route is left unspecified until the MEP contractor arrives, the conduit will be routed for convenience, not for performance. And the glass will tint unevenly.

Comparing retrofit approaches: conduit placement across different partition types

The Hennur partition was load-bearing, which constrained the routing. But even in non-load-bearing partitions, the principle holds. A typical Bangalore retrofit uses one of three partition types:

Dry-lined partition (100mm cavity): Conduit can be routed in the cavity, but must be insulated if within 150mm of the electrochromic glass face. This is the most common retrofit scenario in HSR Layout, Koramangala, and Indiranagar, where older bungalows are being subdivided. The cavity is often used for plumbing and data services, so coordinate the layout early.

Load-bearing concrete (230mm+ depth): Conduit must be routed away from the partition or through the ceiling. This is what the Hennur project faced. The structural engineer should confirm that the cavity zone is available for services; if not, route overhead.

Frameless glass partition (no cavity): The conduit must run on the surface or overhead. Surface routing requires a cable tray or a recessed channel in the adjacent wall. Overhead routing is preferable for electrochromic glass because it removes the thermal influence entirely. This is common in office retrofits but less common in residential work in Bangalore.

Monsoon, hard water, and voltage stability in Bangalore

Bangalore's monsoon humidity (June to September) and hard water (Cauvery TDS typically 200–300 ppm) create a specific challenge for electrochromic glass wiring. The humidity increases the conductivity of dust and moisture in electrical cavities, which can induce leakage currents and voltage drift. The hard water deposits on the glass surface and on any exposed bus bars, increasing resistance.

For electrochromic installations in Bangalore, specify:

• Sealed conduit entries at the transformer and relay boxes (IP54 minimum).
• A surge protector or voltage regulator rated for 24–48V DC, with a response time under 10 milliseconds.
• Annual cleaning of the bus bar terminals with distilled water and a soft brush, to remove mineral deposits.
• If the glass is exposed to monsoon spray or high humidity, apply a hydrophobic coating to the bus bar terminals.

The Hennur retrofit also installed a humidity sensor in the partition cavity, set to trigger ventilation if relative humidity exceeded 75 per cent. This was not strictly necessary for the glass performance, but it protected the transformer and relay from corrosion during the monsoon season.

Specifying smartglass in a retrofit: the coordination workflow

If you are specifying electrochromic glass for a partition retrofit in Bangalore, the workflow should be:

1. Design phase: Nominate the glass type, size, and control requirement (single panel, multiple panels, zoned control). Sketch the electrical route on the RCP.
2. Coordination meeting: Electrical engineer, structural engineer, and glass supplier review the route together. Confirm transformer location, conduit size, and voltage regulation spec.
3. Shop drawing: Glass supplier issues the shop drawing with bus bar positions and electrical connection points marked. Electrical engineer confirms the conduit route and transformer mounting detail.
4. Site installation: Conduit is routed and tested before the glass is delivered. Transformer is mounted and regulated voltage is confirmed (measure with a multimeter at the relay input and at the glass terminals).
5. Glass fitting: The electrochromic panel is fitted and the bus bars are connected. The tint is tested across the full range (clear to opaque) to confirm uniformity.
6. Handover: The control system is commissioned and the client is shown the operation and maintenance schedule.

This workflow takes two weeks longer than a standard partition retrofit. But it eliminates the risk of uneven tinting and the cost of a mid-project correction.

Questions we get asked

Can we relocate the conduit after the glass is fitted?

Not without removing the glass. The bus bars are laminated into the film, and the voltage distribution is determined at the moment of power-up. If the conduit is relocated after installation, the voltage profile across the glass does not change—the tint pattern is already set in the eye of the observer. The only solution is to power down the glass, isolate it, and have the electrical route re-run. This requires the glass to be uninstalled. In the Hennur case, we were fortunate that the glass had not been fully sealed into the frame; the retrofit was possible without removal.

Does the size of the transformer matter for tint uniformity?

Yes. A larger transformer (higher VA rating) runs cooler under load and maintains voltage regulation more tightly. If the distance from the transformer to the glass exceeds 5 metres, or if the conduit must run through a thermally active zone (near HVAC ducts, in direct sunlight, through a hot cavity), specify a transformer one size larger than the calculated load. The extra cost is typically 3,000–5,000 rupees, and it is worth it for peace of mind.

What is the difference between electrochromic glass and retrofit smart film?

Electrochromic glass is toughened glass with the electrochromic layer laminated during manufacture. It is rigid, durable, and performs uniformly if the electrical installation is correct. Retrofit smart film is a polyester film applied to existing glass after installation. It is cheaper and faster to install, but it is more prone to edge-lifting in high humidity and requires more careful electrical routing because the film itself is thinner and more sensitive to voltage variation. For a load-bearing partition retrofit in Bangalore, electrochromic glass is the safer choice if the budget allows.

Can we use a single relay for multiple electrochromic panels?

Yes, but only if the panels are within 2 metres of the relay and the total panel area does not exceed 8 square metres. If the area is larger, or if the panels are spread across the partition, specify a relay for each panel (or a pair of panels). Each relay should have its own conduit run to the transformer. This adds cost but ensures that voltage regulation is independent for each zone and that thermal influence is localised.

How often does the tint need to be recalibrated?

Electrochromic glass does not drift in performance over time if the electrical installation is stable. We recommend an annual check of the voltage regulation (measure the input voltage to the relay and the output voltage at the glass terminals) and a visual inspection of the bus bar connections for corrosion. In Bangalore's hard water and monsoon environment, a five-year replacement of the surge protector and a cleaning of the bus bar terminals is standard maintenance.

Commissioning the retrofit: what to measure on site

When the electrochromic glass is first powered, take these measurements to confirm that the installation is correct:

• Input voltage to the transformer (should be ±5% of nominal, e.g., 230V ±11.5V).
• Output voltage at the relay (should be within ±1V of the rated DC voltage, e.g., 36V ±1V).
• Voltage at the glass terminals (should be within ±2V of the relay output, e.g., 36V ±2V).
• Tint uniformity (observe the glass from multiple angles in clear, mid-tint, and full-opacity states; the tint should be uniform across the panel within a perceptible tolerance of ±5%).

If the voltage at the glass terminals is more than ±2V from the relay output, the conduit is too long, the wire gauge is too small, or the bus bar connection is corroded. Stop and troubleshoot before handing over to the client.

The Hennur retrofit was re-commissioned after the conduit relocation. The voltage at the glass terminals was 35.8V to 36.2V across the panel—well within tolerance. The tint cycled uniformly from clear to 65 per cent opacity. The client did not notice the electrical rework, but they did notice the difference in the glass performance. That is the goal.

If you are planning a retrofit with electrochromic or switchable glass in a Bangalore project, the electrical coordination should begin in the design phase, not on site. Talk to the atelier about your partition type, the distance from the transformer, and the tint uniformity you need. We will work with your electrical engineer to specify the conduit route and the power supply that keeps the tint uniform from edge to edge.