SmartGlass dimming wiring through a partition: why surface-mounted conduit beats in-wall when retrofit relay placement breaks the uniform tint cycle

A master bedroom in Sarjapur Road, mid-retrofit. The architect has specified Notte switchable glass for the west-facing glazing—clear by day, blackout by night. The structural partition between the bedroom and the ensuite runs perpendicular to the window. The electrical contractor proposes running the dimming relay wiring in-wall through that partition. Three weeks into installation, the glass tints unevenly: the section nearest the relay dims to full opacity in 2.3 seconds; the far section takes 4.1 seconds. The uniform tint cycle—critical for the aesthetic and the user experience—is broken.

This is not a rare edge case. Retrofit SmartGlass installations in Bangalore's dense residential stock—from Indiranagar renovations to Whitefield new-builds where partitions interrupt the original electrical runs—encounter this timing drift regularly. The cause is not the glass. It is the voltage drop across a long in-wall conduit run, compounded by relay placement at the partition entry point. The solution is neither expensive nor exotic: surface-mounted conduit, routed externally, with the relay positioned at the power source, not at the load.

Why in-wall conduit through a partition breaks dimming synchrony

SmartGlass dimming—whether PDLC (polymer-dispersed liquid crystal) or electrochromic—operates on a low-voltage DC circuit, typically 24V or 48V, controlled by a relay that switches the voltage on and off. The relay receives a signal from a wall-mounted switch or occupancy sensor, and energises the glass panel through a pair of conductors. The tint transition time—typically 0.5 to 3 seconds for full opacity—is a function of the voltage supplied to the glass at the moment the relay closes.

When the dimming wiring runs in-wall through a structural partition, the conduit length increases. A typical retrofit scenario: the power source (relay and transformer) sits in a ceiling void above the ensuite. The wiring must descend, cross the partition, and rise again to reach the SmartGlass panel on the bedroom side. The in-wall route adds 1.2 to 1.8 metres of additional conductor length compared to a direct external path. At 24V and a typical SmartGlass panel draw of 8 to 12 amps, this extra length introduces a voltage drop of 0.4 to 0.8V across the conductors alone—before accounting for the resistance of the conduit terminations and the relay contacts.

The problem compounds when the relay is positioned at the partition entry point (a common practice, since installers assume the relay should be "close to the load"). The voltage reaching the far section of the glass panel—say, a 1.2m-wide window—is now subject to the voltage drop across the in-wall run, plus the voltage drop across the final 2 to 3 metres of external wiring from the partition to the glass edge. Sections of the panel nearest the relay see 23.6V; sections at the far edge see 22.9V. The tint transition is no longer synchronous. The glass appears to dim in a wave, or in patches.

The case for surface-mounted conduit and relay placement at the source

Surface-mounted conduit—routed visibly along the ceiling or down the wall, then across the partition face—eliminates the in-wall length penalty. A 1.2m surface run replaces a 3.0m in-wall path. The voltage drop across this shorter conduit is negligible (under 0.1V at typical draw). More critically, the relay is positioned at the power source—the transformer and control panel, usually in the ceiling void or a wall-mounted cabinet—not at the partition crossing.

This topology ensures that the voltage supplied to all sections of the SmartGlass panel is nearly identical at the moment the relay closes. The tint transition is uniform across the full width and height of the glass. A 1.5m-wide Notte panel now dims evenly from clear to opaque in 1.8 seconds, not 1.8 to 3.2 seconds across its span.

The aesthetic cost—visible conduit—is real. In a high-end residential project, architects often object to surface-mounted wiring. The atelier's role is to specify it in a way that integrates with the interior language. A brushed-stainless conduit routed along a ceiling beam in an Indiranagar loft reads as intentional, not expedient. A white PVC conduit in a minimalist Koramangala apartment can be detailed to align with trim lines. The alternative—uneven tinting—is not negotiable.

Electrical handover: what the spec must say

The retrofit SmartGlass dimming spec must be explicit about three points: relay placement, conduit routing, and voltage verification at handover.

Relay placement

The specification must state: "The dimming relay shall be mounted at the power source (transformer and control panel location), not at the load (SmartGlass panel location)." This is typically 2 to 6 metres from the glass. The relay controls the supply voltage; it does not sense the load. Placing it at the source eliminates the voltage-drop cascade that occurs when the relay is positioned mid-circuit.

Conduit routing

For retrofit installations where in-wall routing would exceed 2.0 metres or require passage through structural elements, the spec should mandate surface-mounted conduit. The routing should be documented in a shop drawing, with dimensions to the nearest 10mm. Conduit diameter (typically 16mm or 20mm PVC/stainless) should be confirmed by the electrical contractor based on conductor gauge and number; this is not the architect's decision, but the drawing must show the agreed routing so that site deviations are immediately visible.

Voltage verification

At handover, the electrical contractor must provide a voltage-drop certificate, measured at three points: at the relay output, at the panel entry, and at the panel centre. All three readings should be within 0.3V of each other at full load (glass energised and tinting). This is a one-time test; it takes 15 minutes and prevents months of occupant complaints about uneven dimming.

Retrofit SmartGlass in Bangalore's partition-heavy stock

Bangalore's residential boom has produced a particular challenge: many homes built in the 1990s and 2000s (Sadashivanagar, Jayanagar, BTM Layout) have non-structural internal partitions that were added after the original electrical rough-in. A 2015 renovation that introduces Studio partition glass or Privato privacy glass must route dimming wiring across these partitions. The original electrical infrastructure—conduit, cable trays, junction boxes—often does not accommodate the new path. Surface-mounted conduit becomes not a stylistic choice but a practical necessity.

In newer construction (Whitefield, Hebbal, Yelahanka tech-corridor projects), the problem is different: the architect may specify SmartGlass, but the MEP coordination happens late, and the electrical contractor is left to improvise. A clear spec—surface-mounted conduit, relay at source, voltage verification at handover—prevents site improvisation.

Bangalore's climate introduces a secondary consideration: monsoon humidity (June to September) can cause condensation inside poorly sealed in-wall conduit runs, particularly if the conduit passes through an uninsulated void. Surface-mounted conduit, being external and ventilated, is less prone to moisture ingress. In a retrofit scenario where the in-wall route is already compromised by humidity or poor original sealing, surface-mounted conduit is the only reliable option.

When in-wall conduit is acceptable

In-wall routing is acceptable only when: (1) the total in-wall run is under 1.5 metres; (2) the relay is positioned at the power source, not at the partition crossing; and (3) the conduit is sealed at both ends to prevent moisture ingress. These conditions are rare in retrofit scenarios, more common in new-build projects where the electrical rough-in can be coordinated with the SmartGlass specification from day one.

Even then, a voltage-drop certificate at handover is non-negotiable. Do not assume that because the in-wall run is short, the voltage is adequate. Measure it.

Questions we get asked

Can we run the conduit inside the aluminium frame of the SmartGlass panel?

No. The frame is sealed; opening it voids the panel warranty and risks moisture ingress into the electrochromic or PDLC layer. The wiring must be external to the panel, either surface-mounted on the wall or concealed behind trim that does not compromise the frame seal. If the panel is frameless (as in our Cielo Switch overhead installations), the wiring runs in a separate conduit routed adjacent to the glass, never through it.

Does the relay have to be in the same room as the transformer?

No, but it should be within 2 metres of the transformer, on the supply side of the circuit. The relay switches the output of the transformer; placing it at the source ensures that the voltage drop across the wiring to the glass is minimised. If the relay must be remote from the transformer (e.g., in a separate electrical cabinet), the supply wiring from transformer to relay should be oversized (thicker gauge) to reduce voltage drop across that segment.

What if the partition is load-bearing?

Load-bearing partitions complicate in-wall routing because conduit must be threaded through beam pockets or around the structural element, increasing the run length further. Surface-mounted conduit is almost always the better choice. If the architect insists on concealed routing, a structural engineer must review the conduit placement to ensure it does not compromise the partition's load path. This adds cost and complexity; surface-mounted conduit is simpler and faster.

Can we use wireless dimming to avoid the wiring problem altogether?

Wireless dimming systems exist, but they introduce latency (typically 100 to 200 milliseconds) and are subject to RF interference in dense residential buildings. Wired dimming, with proper relay placement and voltage verification, remains the standard for uniform, responsive tint transitions. Wireless is acceptable for occupancy-sensor-triggered dimming where the latency is less noticeable, but not for manual switch control where the user expects immediate response.

How do we detail the surface-mounted conduit so it does not look like an afterthought?

Treat it as a design element, not a utility. Specify a material (brushed stainless, powder-coated aluminium, or white PVC) that complements the interior language. Route it along a natural line—a ceiling beam, a trim line, a column—rather than arbitrarily across a wall. In a minimalist space, a single 16mm white PVC conduit routed horizontally along the ceiling-wall junction reads as intentional. In a more textured interior, a brushed-stainless conduit can align with other metal finishes (door hardware, light fixtures). The key is consistency; if the conduit looks deliberate, the occupant accepts it as part of the design.

Commission a retrofit SmartGlass installation

If your Bangalore project requires SmartGlass dimming across a partition—whether a privacy installation like Privato, a full partition system like Studio, or an overhead application like Cielo—the electrical specification matters as much as the glass specification. Talk to the atelier about relay placement, conduit routing, and the voltage-verification protocol. We work with your MEP consultant to ensure the installation is specified clearly and executed uniformly.