SmartGlass dimming in a Sarjapur Road home office: when the switch logic fails and why

A 3.2-metre frameless partition in a Sarjapur Road home office, electrochromic glass, tinted to full opacity in under five minutes—and the architect's video call drops every time the client hits the dimming switch. Not a fault in the glass. A fault in the wiring logic that nobody coordinated before the electrical rough-in went into the wall. This is the kind of problem that arrives at handover, costs time to diagnose, and teaches you something about smartglass specification that no product datasheet will.

The wiring diagram nobody draws

Electrochromic glass—the kind we commission for conference rooms that disappear or home office partitions—requires a low-voltage control circuit separate from the mains supply. The glass itself draws between 0.5 and 2 amps at 48 volts DC during a tint cycle. That's not much. But the wiring path from the power supply to the glass, and the logic that controls when power flows, has to be specified in a shop drawing before the electrical contractor runs conduit.

Most architects hand this job to the electrical contractor and assume it will be correct. It rarely is. The contractor sees "smartglass" on the spec sheet, sources a dimmer switch from a supplier, and wires it the way they would wire a conventional dimmer for a light fitting. The glass arrives. The wiring is live. And during the tint cycle, the current draw causes a voltage drop in the circuit that trips the router or knocks the WiFi offline.

Why the current draw matters in a home office

When electrochromic glass transitions from clear to tinted—or vice versa—it draws peak current for the duration of the cycle. In a 1.5-metre-wide partition, that cycle lasts between 3 and 5 minutes. During those 180 to 300 seconds, the circuit is active. If the control wiring runs through the same conduit as data cables (Ethernet, WiFi antenna feed, USB), or if the power supply is not adequately stabilised, the electromagnetic noise from the tint cycle will couple into the data lines. On a video call, you see pixellation, audio dropout, or a complete disconnect.

We have seen this on three Whitefield installs and one in Indiranagar. In each case, the electrical contractor had run the low-voltage control circuit and the building's data network through the same 25mm conduit, separated by a single plastic divider. The specification should have required separate conduits, or a minimum 300mm air gap, or shielded twisted-pair cabling with a dedicated return path to ground.

Specifying the control logic before the rough-in

The dimming switch for electrochromic glass is not a simple on-off. It is a logic controller that manages the voltage and duration of the tint cycle. There are three common architectures, and the choice affects how you wire the circuit.

Push-button with built-in timer

The simplest: a momentary push-button wired to a timer module. Press once, the glass tints over 3 to 5 minutes. Press again, it clears. The timer module is a small box, 100 x 80 x 40mm, mounted in the wall or in a junction box near the glass. Current draw is minimal—the module itself draws less than 50mA—and the wiring is straightforward: 48V supply, push-button, return to supply. No logic conflicts. No noise coupling.

The catch: you need a separate push-button for each pane or partition. In a large home office with two or three smartglass elements, you end up with three switches on the wall, which architects usually dislike. And there is no remote control or automation—no integration with building management or voice commands.

Relay-based dimming with remote control

A step up: a relay module wired to a wireless remote or a building-management system. The relay switches the 48V supply on and off, and the glass itself contains a timer that manages the tint cycle. This is what most suppliers recommend for home offices, because it allows one remote to control multiple panes, and it integrates with home automation platforms.

The risk is in the relay itself. A standard electromagnetic relay can generate a voltage spike when it switches off—a transient that couples into adjacent circuits if the wiring is not shielded. The specification must call for a suppression diode across the relay coil, and the control wiring must be in a shielded conduit with a dedicated ground return. If the electrical contractor sources a cheap relay and does not install the diode, the transient will kill your WiFi every time the glass tints.

PWM (pulse-width modulation) control

The most sophisticated: a PWM controller that varies the voltage to the glass, allowing you to set any tint level from 0 to 100 per cent, and to ramp the tint smoothly over a longer period. This is what we specify for home offices where the client wants to dim gradually—say, over 15 minutes—rather than snap to full opacity in 4 minutes.

PWM controllers generate high-frequency switching noise—typically 20 to 50 kHz—which is radiated by the control wiring and the glass itself. Unless the controller is mounted in a shielded enclosure, and the wiring is shielded twisted-pair with a separate ground return, the 20kHz signal will couple into your data cables and degrade WiFi signal strength by 20 to 40 per cent. We have measured this with a spectrum analyser on two Whitefield installs. In one case, the WiFi access point lost signal entirely during the tint cycle.

The shop drawing you need to commission

Before the electrical rough-in, the architect and the electrical contractor must agree on a single document: a control schematic that shows the power supply, the control module, the switch or remote receiver, the wiring paths, and the conduit routing. This drawing should specify:

• The voltage and current rating of the power supply (48V DC, minimum 5 amps for a single large pane)
• The type of control module (push-button timer, relay, or PWM) and its exact model number
• The gauge and shielding of all low-voltage wiring (typically 2.5mm² twisted-pair, shielded, for runs longer than 10 metres)
• The conduit type and routing: separate from data cables, or shielded if shared
• The ground return path: a dedicated copper conductor back to the power supply, not shared with the building earth
• The location of the control module enclosure and the switch or remote receiver

This drawing does not exist on most Bangalore projects. The electrical contractor treats smartglass as a light fitting and wires it accordingly. The result is a partition that works, but only when you are not on a video call.

Fallback logic when automation fails

Even with a correct wiring specification, smartglass control systems can fail. The relay can stick. The PWM controller can lose power. The remote receiver can malfunction. In a home office, this is not acceptable—the client needs to be able to tint the glass manually, without waiting for a technician.

The fallback is a hardwired push-button, independent of the automation system. This button is wired directly to a timer module, with its own 48V supply and ground return. If the main control system fails, the button still works. The glass still tints and clears, even if the remote or the building-management system is offline.

We specify this on every smartglass installation in a home office or bedroom. It costs an extra 3,000 to 4,500 rupees for the timer module and the button, and it eliminates the risk of being locked out of the glass when the automation fails. Most architects do not think to ask for it, and most suppliers do not offer it unless prompted.

Moisture and the monsoon: why the power supply matters

Bangalore's monsoon humidity—June through September—can reach 80 to 90 per cent. The Cauvery water TDS sits between 200 and 300 ppm, which means condensation on glass surfaces is acidic and corrosive. If the 48V power supply is mounted in an uninsulated junction box on the external wall of the home office, moisture will corrode the terminals and the relay contacts. The glass will still tint, but the control circuit will become intermittent: the switch works sometimes, fails other times, and eventually stops working altogether.

The specification must require the power supply to be mounted in a sealed, desiccant-lined enclosure, or indoors in a climate-controlled space. If the home office is on the north side of the building and receives direct monsoon wind-driven rain, the enclosure should be IP65-rated (dust-tight and protected against low-pressure water jets). This adds cost and complexity, but it is the only way to ensure the control system survives the monsoon.

Questions we get asked

Can we use a standard light dimmer switch for smartglass?

No. A standard dimmer is designed for resistive loads (incandescent bulbs) or inductive loads (transformers), not for the capacitive load of electrochromic glass. The dimmer will overheat, and the glass will not tint evenly. You need a control module designed for electrochromic glass, with a timer or PWM circuit specific to the load characteristics of the glass.

Why does the glass tint unevenly, with dark patches at the top and clear patches at the bottom?

Uneven tinting is usually caused by inadequate voltage at one end of the glass. If the control wiring is undersized (too thin), the voltage drop over the length of the circuit causes the far end of the glass to receive less voltage and tint more slowly. The specification should require the wiring to be sized so that the voltage drop is less than 2 per cent of the supply voltage. For a 48V supply and a 15-metre run, use 4mm² copper conductors, not 2.5mm².

Can smartglass be controlled by voice, or by a smartphone app?

Yes, but it requires a wireless control module (WiFi or Zigbee) and a separate control circuit. The wireless module receives the command from the app or voice assistant, and sends a signal to the relay or PWM controller. This adds cost and complexity, and introduces another failure point—if the WiFi is down, the glass cannot be controlled. We recommend a hardwired push-button as a fallback, so the glass can always be tinted manually, even if the app or WiFi is offline.

How long does an electrochromic glass partition last before the glass stops tinting?

The electrochromic coating is rated for 100,000 to 200,000 cycles. At one tint cycle per day, that is 270 to 550 years. In practice, the control circuit fails long before the glass does. The relay sticks, the power supply fails, or the wiring corrodes. The glass itself is durable. The control system is the weak point.

Can we retrofit smartglass dimming to an existing clear glass partition?

Only if the partition is a single pane of glass at least 6mm thick. Retrofit smart film can be laminated to the surface, and a control system can be added. But the partition must be removed from the frame, the film applied in the atelier, and the partition reinstalled. This is expensive and time-consuming. It is cheaper to specify smartglass in the initial design than to retrofit it later.

Commission a control specification with the atelier

Before your electrical contractor runs conduit, talk to us about the control logic for your smartglass partition. We can provide a shop drawing that specifies the power supply, the control module, the wiring, and the conduit routing—everything the electrical contractor needs to install it correctly the first time. Bring your site dimensions, your RCP showing the partition location, and your electrical contractor's contact details. We will coordinate the specification with them, and you will avoid the video-call dropout and the fallback to manual control.