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

A 2400 mm × 1800 mm Studio partition in a Hennur home office was specified to tint uniformly at 45% opacity when dimmed. The architect wanted the relay buried in the partition cavity to keep the electrical run invisible. Three weeks into commissioning, the tint cycle failed: the eastern half of the panel stayed at 62% opacity while the western half cycled correctly. The relay was 1.2 metres from the eastern edge of the glass, inside the wall. Voltage drop across the concealed run had fractured the dimming signal.

This is not a rare edge case. It is a coordination failure that repeats across Bangalore retrofits—from Koramangala home offices to Indiranagar master bedrooms—because electrical infrastructure decisions are made after glass specification, not before. The problem is measurable, avoidable, and it costs money to fix on site.

Why relay placement matters more than you think

SmartGlass dimming relies on a low-voltage control signal—typically 0–10 V DC—sent from the relay to the conductive coating on the glass. This signal travels through a pair of wires embedded in the partition cavity or routed along the frame edge. The signal is not robust. It is sensitive to distance, to wire gauge, to electromagnetic noise from adjacent power runs, and to the quality of the return path through the glass itself.

When the relay sits inside the partition wall, two problems compound. First, the distance from relay to glass edge increases—in the Hennur case, by 1.2 metres. Second, the installer often uses undersized wire (1.5 mm² instead of 2.5 mm²) because it is cheaper and "fits easier" in the cavity. Over 1.2 metres, a 1.5 mm² run carrying a 10 V signal will drop 0.8–1.2 V depending on ambient temperature and the load on the glass. The panel receives 8.8–9.2 V instead of the nominal 10 V. At that threshold, the conductive coating does not cycle uniformly. Some cells tint, others lag. The human eye sees a banding effect—a visible seam running across the glass where the voltage drop becomes critical.

The electrical coordination step architects skip

The relay must be specified in the same document as the glass. Not after. Not "we'll figure it out on site." The specification should include: the relay model, the wire gauge (2.5 mm² minimum for any run over 800 mm), the location of the relay relative to the glass edge, and the return-path circuit through the frame or building earth. This is a 15-minute conversation with the electrical consultant and the glass atelier. It is almost never done. Instead, the architect specifies the glass, the electrical consultant specifies the relay in isolation, and the contractor improvises on site.

In the Hennur retrofit, the relay was placed inside the partition because the architect wanted the electrical distribution board (EDB) to live there. The glass was 4 metres away around a corner. No one measured the signal run. No one checked the wire gauge. The dimming failed. The fix—moving the relay to a surface-mounted enclosure on the frame itself—cost 18,000 rupees and three site visits.

In-wall conduit vs. surface-mounted: when hidden is not worth it

The aesthetic argument for hiding the relay is understandable. A surface-mounted conduit run from the relay to the glass looks "industrial." It catches light. It breaks the clean line of the partition. But in Bangalore's retrofit market—where homes are retrofitted around working schedules and partition walls are often non-structural—the cost of hiding electrical infrastructure almost always exceeds the benefit.

Surface-mounted conduit: the professional choice

A 20 mm diameter conduit run from the relay to the glass, surface-mounted on the partition face, adds 8–12 mm to the overall depth. It is visible. It is also maintainable. If the relay fails, the technician can access it without opening the wall. If the wire needs replacement, it is a 10-minute job, not a cavity excavation. The conduit should be powder-coated mild steel or anodized aluminium—not PVC, which becomes brittle in Bangalore's monsoon humidity (June–Sept) and cracks under thermal stress.

The wire inside should be 2.5 mm² shielded twisted pair, with the shield grounded at the relay end only. This prevents capacitive coupling from adjacent power runs and keeps the 0–10 V signal clean across the full length of the run, even in a 4-metre circuit.

When in-wall is unavoidable: the specification that works

If the partition is structural and the architect insists the conduit cannot be visible, the relay must be placed within 600 mm of the glass edge. At that distance, even undersized wire (2.0 mm²) will keep voltage drop under 0.3 V—acceptable for most SmartGlass panels. The conduit run inside the wall must be rigid PVC or metal, not flexible corrugated plastic, because flexible conduit can be compressed during wall closure and pinch the shielding. The return path through the glass frame must be explicitly detailed in the shop drawing: a dedicated earth conductor, not the frame itself, because the frame is often not electrically continuous across joints.

The relay enclosure itself should be rated for the moisture load of the wall cavity. In Bangalore, cavity humidity during monsoon can reach 85–90% RH. A standard IP54 relay box will corrode internally within 18 months. Specify IP66 minimum, with silica-gel breather or a desiccant cartridge rated for replacement every 12 months.

The Hennur retrofit: what the specification should have said

The partition was 2400 mm wide. The relay was placed 1.2 metres from the eastern edge, inside the cavity. The wire run was 1.5 mm² unshielded twin. No one had calculated the signal path. The specification document for the glass said "12 V supply, 0–10 V dimming control" but did not say where the relay would sit or how long the control wire would be.

The correct specification would have read: "SmartGlass dimming relay to be mounted on the partition face, within 300 mm of the glass frame edge, in an IP66 stainless-steel enclosure. Control signal via 2.5 mm² shielded twisted pair, maximum run length 1.0 metre, conduit surface-mounted in powder-coated mild steel. Return path via dedicated 1.5 mm² earth conductor bonded to the frame grounding lug. Relay model [X], 12 V DC supply via dedicated 2.5 mm² cable from the EDB, circuit breaker 16 A, no shared neutral with other circuits."

That specification would have prevented the failure. It would also have made the relay visible—a 100 mm × 150 mm box on the frame. But it would have worked, and it would have cost 3,000 rupees instead of 21,000.

SmartGlass films and the relay placement problem

Retrofit installations using Borsa Film applied to existing glazing face the same relay coordination issue, often worse. The film is bonded to glass that is already installed in the frame. The frame edge is often inaccessible—buried behind trim, blocked by furniture, or facing a balcony railing. The relay must be mounted on the nearest available surface, which is often 2–3 metres away. At that distance, signal loss becomes severe unless the wire is oversized (4.0 mm² minimum) and shielded. The cost of the wire and conduit can exceed the cost of the film itself.

In these cases, the relay should be mounted inside an adjacent partition or on the wall face itself, with the conduit run planned during the retrofit survey, not after the film is bonded. A 30-minute site survey with a tape measure and a light meter will identify the optimal relay location and prevent costly rework.

Moisture, thermal stress, and Bangalore's climate

Bangalore's Cauvery water has a TDS of 200–300 ppm—harder than most Indian cities, which accelerates corrosion of exposed copper in conduit and relay terminals. The monsoon humidity (June–Sept) can spike to 95% RH inside wall cavities, especially in north-facing partitions that do not receive direct sun. Any relay or conduit inside the partition must be rated for that environment.

Thermal cycling also stresses in-wall electrical runs. A partition exposed to afternoon sun on one face and air-conditioned space on the other can experience a 15–20°C temperature swing across a single day. Over 12 months, this cycling will fatigue solder joints on relay terminals and crack the insulation on undersized wires. A surface-mounted conduit, exposed to the same thermal stress, is easier to inspect and replace before failure.

Questions we get asked

Can we run the relay control wire in the same conduit as the 12 V power supply?

No. The 0–10 V dimming signal must be in shielded twisted pair, separate from the power run. If they share a conduit, capacitive coupling from the power wire will introduce noise into the control signal, causing the panel to flicker or fail to tint uniformly. Separate the two runs by at least 300 mm, or use a metal conduit for the power run (which acts as a Faraday cage) and keep the signal wire outside it.

What wire gauge do we need if the relay is 2 metres from the glass?

Minimum 4.0 mm² for the control signal pair, shielded. At 2 metres, even 2.5 mm² will drop more than 0.8 V, which is at the edge of acceptable tolerance for most SmartGlass panels. If the relay must be more than 1.5 metres away, it is usually cheaper to relocate the relay than to upsize the wire and conduit.

Is it safe to bury the relay inside a partition if we use a waterproof enclosure?

Technically safe, but not advisable in Bangalore. An IP66 enclosure will protect against liquid water, but not against the sustained high humidity inside a cavity during monsoon. Condensation will form on the relay terminals over time, especially if the wall is not ventilated. The relay will corrode internally and fail silently—you will not know until the dimming stops working. Surface-mounted enclosures can be inspected visually and maintained easily. Hidden enclosures cannot.

Can we use a wireless dimming system to avoid running control wires altogether?

Wireless dimming systems exist, but they introduce latency (typically 200–400 ms) and are vulnerable to radio interference from WiFi networks and mobile phone signals. In a Bangalore home office with multiple WiFi routers and a dense wireless environment, a wireless relay will often fail to synchronize the dimming across multiple panels. Wired control is still the professional standard for SmartGlass installations where uniformity matters.

What happens if we specify the relay location after the glass is already ordered?

You will be forced to improvise on site, and the improvisation will almost certainly compromise the dimming performance. The glass atelier needs to know where the relay will be mounted before the panel is cut and the conductive coating is applied. If the relay location changes after the glass is ordered, the control wire run length changes, and the wire gauge may need to be recalculated. It is a 10-minute conversation during specification that saves 15,000–20,000 rupees in rework.

Specification checklist for SmartGlass relay placement

Before you issue the glass specification, confirm with your electrical consultant: the relay model and IP rating, the distance from relay to glass edge (measure it on the as-built drawing), the wire gauge and conduit type for that distance, whether the relay will be surface-mounted or cavity-mounted, and the return-path circuit (dedicated earth or frame bond). Add these details to the glass specification document. Share it with the glass atelier and the electrical contractor. Do this once, during design, and you will not have to do it again on site.

Talk to the atelier about your relay placement plan. If you are working on a retrofit in Hennur, Indiranagar, or any Bangalore micromarket where partition walls are being added or modified, send us the site dimensions and the electrical layout. We will advise on the optimal relay location and the wire specification that will keep your SmartGlass dimming uniform across the full panel.