SmartGlass wiring in a partition: why surface-mounted conduit beats in-wall when retrofit dimming breaks the tint uniformity

A Hennur architect specified a 6mm clear partition for a home office last year, then called us four months after handover: the client wanted dimming added, and the electrician had already chased the wall. The conduit was routed inside the stud cavity, the relay box was mounted at the far end of the partition, and humidity from the monsoon had begun pooling inside the conduit sheath. The glass tint was mottling—not uniformly blue, but patchy, with lighter zones near the wiring cavity. The problem was not the glass. It was the path the current took to reach it.

Why retrofit wiring breaks tint uniformity in partitions

Electrochromic glass—what we call smartglass—tints by applying a low-voltage DC current across a suspended particle or polymer dispersed liquid crystal film. The current needs to reach every part of the glass surface evenly. When the wiring is routed through the partition cavity, three things go wrong in sequence: heat builds up inside the conduit, humidity condenses on the relay contacts, and the voltage drop becomes uneven across the glass width.

In Bangalore's monsoon season (June to September), the air inside a timber-frame partition can reach 85–90% relative humidity. A sealed conduit running through that cavity becomes a condensation trap. The relay contacts—typically rated for 24V DC switching—begin to oxidise. The voltage arriving at the glass connector drops from 24V to 22V or lower. A smartglass panel 1200mm wide will tint unevenly: the end closest to the relay tints first and darker; the far end lags. Over weeks, this creates visible striping or mottling, especially in north-facing rooms where the glass is under less solar load.

The case for surface-mounted conduit in retrofit scenarios

Surface-mounted conduit—run along the face of the partition frame, not through it—solves three problems at once. First, it stays cooler because air circulates around it. Second, any condensation drains out of the conduit ends rather than pooling near the relay. Third, the voltage path is shorter and cleaner: relay to connector in a straight line, typically 0.5–1.5 metres, versus 3–4 metres through a cavity with bends and compression points.

We fitted a Hennur home office with 20mm surface-mounted PVC conduit last month. The relay box was mounted on the adjacent wall, 400mm from the partition edge, with the conduit run at 45 degrees to the glass connector. The tint is now uniform across the full 1400mm width. The client has not reported any mottling in the three weeks since handover.

Shop drawing discipline matters more than the spec

The architect's original spec said "24V DC wiring to smartglass, conduit to be concealed where possible." That language opened the door to the in-cavity route. A shop drawing changes that conversation. Before we start fabrication, we draw the conduit path at full scale, showing the relay box position, the voltage drop calculation (typically 0.8–1.2V over the run), and the humidity-control strategy. The drawing becomes the contract between the glass atelier, the electrician, and the site team.

In retrofit work especially, the shop drawing is not a courtesy. It is the only place where the electrical coordination gets locked down before the partition is sealed. We ask for the relay box location before the frame goes up. We specify the conduit gauge, the connector type, and the drainage holes at the bottom of the conduit run. None of this appears in a standard spec sheet.

Relay placement and voltage drop in Bangalore partitions

A 24V DC relay for smartglass typically draws 15–20mA when switching. Over a 4-metre copper run in 20mm conduit, the voltage drop is roughly 1.5V. Over a 1.5-metre surface-mounted run, it is 0.5V. That difference is the difference between uniform and mottled tint.

We specify relay placement using this rule: the relay box should be within 1.5 metres of the glass connector, mounted on a solid wall or column, not on the partition itself. If the partition is load-bearing or in a high-traffic area (like a Koramangala open-plan home office), the relay goes on the adjacent structural wall. If the partition is a demising wall between two rooms, the relay goes on the side where the smartglass control will be most intuitive—typically the room where the user sits.

Humidity control in the conduit

Sealed conduit in a timber partition is a humidity trap. We drill two 6mm drainage holes in the bottom of the conduit run—one at the relay end, one at the glass connector end—and fit them with Gore-Tex breather plugs. These allow air to circulate but prevent insects and dust from entering. The cost is negligible; the benefit is a dry relay contact and no voltage drop creep over six months.

In high-humidity rooms (bathrooms, kitchens, rooms with large windows facing the monsoon), we recommend surface-mounted conduit as standard, regardless of whether the retrofit is planned. It costs 15–20% more to install than in-cavity routing, but it eliminates the mottling risk entirely and makes future dimming retrofits trivial.

Tint uniformity and the role of the connector

The glass connector—the point where the conduit meets the smartglass—is as critical as the relay. A loose connector or corroded terminal will create a high-resistance point, causing the voltage to drop sharply across just that connection. The tint will fail to activate, or activate only partially, on the side of the glass nearest the connector.

We use gold-plated connectors rated for 24V DC, with a contact resistance under 0.05 ohms. The connector is soldered, not crimped, to the lead wire inside the conduit. Before the partition is sealed, we test the circuit at full voltage and measure the voltage at the glass terminal. If it reads below 23V, we investigate the conduit run and relay placement before signing off.

When to retrofit versus when to spec from the start

Retrofit dimming into an existing partition is a legitimate brief—clients often add smartglass years after a home office is finished. But the electrical cost of retrofit is higher than the cost of specifying it at design stage. If dimming is even a possibility, we recommend routing the conduit during the initial build, leaving it dead until the relay and control system are installed. The conduit costs 3000–4500 rupees. Retrofitting later costs 8000–12000 rupees and risks the tint uniformity.

For new partitions in Bangalore residential projects, we work from the RCP and electrical plan to position the relay box before the partition frame is erected. We specify the conduit type, gauge, and route on the shop drawing. The electrician installs the conduit during the rough-in phase, not after the partition is sealed. This discipline—which costs nothing extra and takes no extra time—eliminates every mottling problem we have seen in the past five years.

The broader lesson: smartglass is not just glass

Electrochromic film is a material, but smartglass is a system. The glass, the relay, the conduit, the connector, and the control logic are interdependent. A spec that treats the glass in isolation—"specify 6mm smartglass, tint range blue to clear"—will fail in retrofit scenarios. A shop drawing that treats the glass as part of an electrical circuit will succeed.

We have fitted partitions with integrated dimming control in Indiranagar and Sadashivanagar where the relay box is mounted inside the partition frame itself, in a sealed enclosure with its own humidity control. We have also retrofitted privacy glass into existing bathrooms where surface-mounted conduit was the only viable option. Both approaches work. The difference is that one was drawn before the first nail was driven.

Questions we get asked

Can we run smartglass wiring through the same conduit as the partition's regular electrical circuits?

No. 24V DC smartglass wiring must be isolated from mains voltage circuits. The relay generates electromagnetic noise when switching, and this noise couples into mains-voltage wires if they share a conduit. Specify separate conduit for smartglass, even if the relay box is on the same wall as the main distribution board.

What happens if we don't install humidity control in the conduit?

The relay contacts will oxidise within 6–12 months in Bangalore's monsoon climate. The voltage drop will increase, and the tint will begin to mottle. You may not see it immediately, but by the second monsoon season, the mottling will be visible. Replacing the relay is a 4000–6000 rupee fix, but it requires the partition to be opened up.

Is surface-mounted conduit visible, and does it affect the partition's appearance?

Yes, it is visible. We typically run it along the bottom edge of the partition, 50–100mm above the floor, where it is less noticeable. In some designs, we paint it to match the partition frame or the wall colour. If aesthetics are critical, we can conceal the conduit in a timber or plaster chase along the partition edge—but this requires the chase to be vented and drained, which costs more than surface-mounting.

Can we add dimming to smartglass that was installed without conduit?

Yes, but the cost is higher and the risk of mottling is real. We would route surface-mounted conduit from the relay box to the glass connector, which means either running it visibly along the partition face or opening up the partition cavity to chase it. Either way, budget 8000–12000 rupees and allow 3–4 days on site.

Do we need a separate power supply for the relay, or can it draw from the main DB?

The relay draws 24V DC, which must come from a dedicated transformer or DC power supply. It cannot be drawn from the main distribution board. Specify a 24V DC power supply rated for at least 2A, mounted near the relay box. The supply itself should be in a sealed enclosure with its own humidity control if it is in a damp location.

Bringing it together

Smartglass retrofit work in Bangalore homes requires the same electrical discipline as the original build, with one addition: the shop drawing must account for humidity, voltage drop, and conduit routing before the first tool touches the partition. Surface-mounted conduit is not a compromise—it is the correct choice for retrofit scenarios and for any partition in a high-humidity zone. Talk to the atelier before your electrician makes the routing decision. The tint uniformity depends on it.