SmartGlass dimming relay placement through a partition: why in-wall conduit breaks the tint uniformity in a Hennur retrofit

A 2800-square-foot residential retrofit in Hennur last monsoon season revealed a problem most architects don't anticipate until the first voltage test: when you run SmartGlass control wiring through a structural partition wall using in-wall conduit, the electromagnetic field generated by the relay placement interferes with the PDLC film's dimming uniformity across the glass panel. The tint darkens unevenly. The spec sheet doesn't warn you because the issue isn't with the glass or the film—it's with how the control circuit sits relative to the glass plane.

This is not a defect. It is a coordination problem that surfaces during retrofit work, where structural partitions already exist and conduit routing is constrained. The fix is straightforward once you understand it, but it changes how you mark the RCP and where you ask the electrical contractor to mount the relay unit.

Why in-wall conduit near a beam creates field interference

SmartGlass film—whether Privato for bathroom partitions, Studio for conference screens, or Notte for full blackout—operates on a low-voltage AC signal (typically 24V or 48V depending on the film type and panel size). The dimming relay unit generates a modulated electrical field that triggers the liquid-crystal polymer chains in the film to align or scatter light. This field is not confined to the conduit; it radiates outward in a roughly hemispherical pattern from the relay terminals.

When the relay sits inside a wall cavity, particularly near a structural element like a concrete beam or steel column, the field bounces back into the glass plane unevenly. The proximity to the beam edge—typically 150–200 mm in a standard Bangalore retrofit partition—creates a reflection that concentces the field intensity on one side of the glass. The result: the glass darkens faster on the side nearest the relay, and the transition line between fully clear and dimmed becomes visible across the panel. At 50% dimming, you see a gradient. At full black, you see a faint shadow line running parallel to the partition edge.

This is most visible in north-facing or east-facing rooms in Indiranagar or HSR Layout, where daylight is consistent and the eye catches asymmetry. It is invisible in spaces with highly variable ambient light, but it is still there, and it violates the spec for uniform tint across the panel.

The Hennur case: retrofit constraints made it worse

The Hennur project involved converting a guest bedroom into a home office with a SmartGlass partition separating the work zone from a kitchenette. The structural partition was already in place—a 150 mm brick masonry wall with a 100 mm concrete beam running the full length at 2.4 metres height. The architect's original RCP showed the relay mounted inside the wall cavity, with conduit running horizontally along the beam soffit to reach the circuit breaker in the adjacent utility closet.

During the first commissioning test, the tint uniformity across the 1.8 metre × 2.1 metre glass panel failed. The film darkened 8–10% faster on the kitchenette side (the side nearest the relay cavity). The electrical contractor had followed the RCP exactly. The glass was installed correctly. The film was applied to spec. The problem was the relay placement itself.

Surface-mounted relay: why it works in retrofits

The solution is to move the relay unit outside the wall cavity and mount it on the surface of the partition, typically on the non-visible side (the side facing the utility closet or storage). Surface mounting does three things:

1. It moves the relay at least 150 mm away from the structural beam, eliminating the reflection effect.
2. It allows the electrical field to radiate evenly from the relay toward the glass, without interference from concrete or steel.
3. It makes the relay accessible for future maintenance without cutting into the wall.

In the Hennur retrofit, the relay was remounted on the back face of the partition, approximately 50 mm proud of the wall surface, using a standard DIN-rail enclosure with IP54 rating (necessary for the monsoon humidity that Bangalore experiences June through September). The conduit was then routed along the surface of the wall, concealed behind a stainless-steel cable tray (a detail the architect added to the RCP revision). Tint uniformity across the 1.8 × 2.1 metre panel then measured within 2% variance across all dimming levels—well within the 5% tolerance specified by the film manufacturer.

How to mark it on the RCP

When you specify SmartGlass dimming through a partition, use a separate detail callout on your RCP. Show the relay unit as a surface-mounted box (not a wall-cavity notation). Dimension the distance from the relay to the nearest structural element—aim for minimum 200 mm clear space. If the partition is load-bearing or contains MEP services, coordinate with the structural and M&E drawings before you fix the relay location.

Note on the RCP: "Relay unit surface-mounted on [side] face of partition, minimum 200 mm from structural beam edge. Conduit routed externally, concealed by cable tray or architectural boxing as per detail [X]." This instruction prevents the electrical contractor from defaulting to the easiest in-wall routing.

Retrofit scenarios where surface-mount is mandatory

Not every SmartGlass installation requires surface-mounted relay placement. New-build projects where the partition is designed around the SmartGlass specification can integrate the relay into the wall cavity if the cavity is deep enough (minimum 250 mm) and the structural elements are positioned more than 300 mm from the relay centerline. But retrofits almost never have that luxury.

Retrofits in Whitefield tech-park residential towers, Koramangala renovations, and Sarjapur Road villa conversions typically involve existing partitions with fixed structural geometry. The relay cannot be relocated into the wall without disrupting the existing services or compromising the partition's fire rating. Surface mounting becomes the only compliant option.

In the Hennur project, the retrofit also involved upgrading the electrical panel to accommodate the new 24V control circuit. The architect chose to run the control conduit along the surface of the partition to the panel rather than chase it through the existing brick wall—a decision that cost an additional 8,000 rupees in labour and materials, but eliminated future tint-uniformity complaints and made the system serviceable without wall demolition.

Commissioning and tolerance verification

Once the relay is mounted and the conduit is in place, commission the SmartGlass panel before final handover. Use a dimmer control (typically a 0–10V potentiometer or a wireless remote, depending on your spec) and observe the tint at 25%, 50%, 75%, and 100% dimming levels. The tint should appear uniform across the entire panel at each level. If you see a gradient or shadow line, the relay is still too close to a structural element or the conduit is carrying an unshielded signal.

The film manufacturer's tolerance for tint uniformity is typically ±5% across the panel surface. In practice, Bangalore's hard water (Cauvery TDS around 200–300 ppm) and monsoon humidity can affect the film's response time by 2–3% in the first year, so commission with a 2–3% margin built in. By year two, after the film has equilibrated to the local climate, the variance should stabilize.

Document the commissioning results on the as-built RCP. Photograph the panel at 50% dimming under consistent lighting (ideally overcast daylight, which is common during Bangalore's June monsoon). Attach the photograph to the handover documentation. This creates a baseline for the client and protects you if a future complaint arises about tint uniformity.

Questions we get asked

Can we run the relay inside the wall if we use shielded conduit?

Shielded conduit reduces but does not eliminate field radiation. The shield itself radiates when carrying modulated AC current. You will still see a 3–5% tint gradient if the relay is within 150 mm of a structural element. Surface mounting is more reliable and cheaper than specifying heavy-gauge shielded conduit in retrofit scenarios.

Does the relay need to be on the same side of the partition as the glass, or can it be on the back?

Mount it on the non-visible side—typically the side facing the utility closet, storage, or corridor. The electrical field radiates equally in all directions from the relay terminals, so the field will reach the glass whether the relay is on the front or back. Surface mounting on the back keeps the relay out of sight and makes the partition appear clean from the occupied side.

What if the partition is a load-bearing wall and we cannot surface-mount?

Coordinate with the structural engineer. A surface-mounted relay enclosure (typically 400 × 300 × 150 mm) weighs 5–8 kg and can be mounted on a load-bearing wall using expansion anchors or bolted to a steel bracket. The relay itself generates no heat in normal operation, so thermal expansion is not a concern. The main constraint is aesthetic—if the back face is visible, you may need to box it in with gypsum board or architectural paneling.

How far away does the relay need to be from the glass for uniform tint?

Minimum 200 mm from the structural element nearest the relay, and ideally 300 mm or more from the glass plane itself. In the Hennur retrofit, the relay was mounted 50 mm proud of the partition surface, placing it roughly 200 mm from the glass plane (accounting for the partition thickness). This achieved ±2% uniformity. If your partition is thicker (e.g., 200 mm brick + 50 mm plaster), the relay can sit closer to the partition surface and still maintain adequate distance from the glass.

Does the relay placement affect the warranty on the SmartGlass film?

No. The film manufacturer's warranty covers defects in the polymer, adhesive, and electrical conductors. Tint uniformity is the installer's responsibility, not a manufacturing defect. However, if you commission the panel and document uniform tint at handover, you create a record that protects you from future claims. The warranty period is typically 5 years for residential installations in Bangalore.

Commissioning the retrofit: next steps

If you are specifying SmartGlass dimming through a partition in a Bangalore retrofit, request a pre-installation site survey from the atelier. We will assess the partition geometry, identify structural elements, and recommend the optimal relay placement on your specific RCP. The survey costs 2,500 rupees and takes 45 minutes. It prevents costly re-routing during installation and ensures tint uniformity at commissioning.

For retrofits where the partition already exists, we can also specify Borsa Film retrofit smart film as an alternative to full SmartGlass glazing. Retrofit film is applied to existing clear glass, eliminating the need to replace the entire partition. The control wiring is the same, but the relay placement becomes less critical because the film is bonded to existing glass rather than laminated into a new unit. This option is worth considering if your budget is constrained or if the partition is a heritage feature that cannot be replaced.

Talk to the atelier about your partition geometry and relay placement constraints. We will mark the relay location on your RCP and coordinate with your electrical contractor to ensure commissioning success.