Electrochromic SmartGlass for a Devanahalli villa facade: wiring from the electrical panel, switch logic and the five-minute tint cycle

A west-facing study in Devanahalli, triple-height glass, afternoon sun at 4 PM in March. The architect had spec'd electrochromic glass to manage glare without external louvers. The electrical contractor called two days before handover: no one had told him the glass needed low-voltage DC, and he'd chased 230V AC to the window head. We pulled the chase open, ran 2-core shielded cable back to a step-down transformer near the panel, and re-commissioned the tint cycle. The client now dims the facade from a wall switch in under five minutes, but the coordination gap cost three days and a re-plaster. This is the wiring brief we now send with every electrochromic specification.

What electrochromic glass is and why the electrical coordination matters

Electrochromic glass darkens when you apply a low-voltage DC current—typically 24V, 48V, or 60V depending on the make. A metal-oxide coating inside the laminate changes ion distribution under voltage, shifting the pane from clear (visible light transmittance ~62%) to tinted (~2-5%) in a controlled ramp. Unlike PDLC switchable film that toggles opaque-to-clear in under a second, electrochromic transitions over four to six minutes, holding intermediate states without continuous power once the tint is set. That makes it ideal for solar-heat management on large facades where you want gradual dimming, not binary privacy.

The electrical challenge: electrochromic glass is a capacitive load, not a resistive one. You cannot wire it to mains AC. Every installation requires a dedicated low-voltage DC supply—usually a DIN-rail transformer mounted in or near the main distribution board—and shielded cable run in the wall chase to each glazed opening. The cable gauge depends on run length and pane area; for a 3m × 2.4m lite on a 20m run, we typically spec 1.5 mm² 2-core shielded. The shield ties to earth at the transformer end only, never at both ends, to avoid ground loops that can cause flicker or incomplete tint.

Transformer placement and panel coordination

The step-down transformer should sit within 25 metres of the farthest electrochromic pane to minimise voltage drop. In most Bangalore villas the main panel is in a ground-floor service yard or under-stair cupboard; if the electrochromic facade is on the first floor, consider a sub-panel or a wall-mount enclosure near the stairwell. The transformer itself is a sealed module, roughly 180 mm × 120 mm × 60 mm, with screw terminals for AC input and DC output. It draws between 40W and 150W during the tint cycle, then drops to under 5W in hold mode. Mark it clearly on the electrical single-line and call it out in the panel schedule so the contractor prices the breaker and cable correctly.

Coordinate with the glass supplier on input voltage. Some European electrochromic systems expect 48V DC; others use 60V. The transformer must match. If you substitute a generic SMPS unit to save cost, check the ripple spec—electrochromic coatings are sensitive to AC ripple above 5%, which can cause uneven tinting or premature coating fatigue. We've seen one Sarjapur Road project where a contractor used a cheap LED-driver transformer; the glass tinted in patches and the warranty was voided.

Cable routing: chase depth, bends, and pull-box locations

Run the DC cable in a separate chase or conduit from AC lighting and power—electromagnetic interference from AC cables can induce noise on the DC line, especially if the run is long. A 25 mm PVC conduit is usually adequate for a single 2-core cable; if you're feeding multiple lites from a single transformer, upsize to 32 mm and pull all DC cables together. Avoid sharp 90° bends; electrochromic cable is stiffer than standard twin-flex because of the shield braid. Use long-radius bends or pull boxes at every second turn.

Terminate the cable at a junction box behind the window frame head, then connect to the glass via a weatherproof plug or screw-terminal block supplied by the glass manufacturer. The connection must be accessible for commissioning and service—do not bury it in the wall. If the facade is unitised curtain-wall, the junction box typically sits in the mullion cavity; for site-glazed openings, mount it on the reveal soffit and dress the cable through a drilled hole in the frame. Seal the hole with silicone after pull-through to maintain the frame's thermal break.

Switch logic: manual override, timer, and sensor integration

Manual wall switch

The simplest control is a momentary push-button wired to a relay module at the transformer. One press initiates the tint cycle (clear → dark); a second press reverses it (dark → clear). The relay module holds the intermediate state without further input. Mount the switch at standard height—1.2 m above finished floor—near the room entry or adjacent to the light switches. Use a metal-clad switch plate, not plastic, to match the rest of the electrical fittings; we've found that clients read a plastic switch as temporary and ask for it to be changed during the snag walk.

Timer and astronomical clock

For west-facing facades in Bangalore, a timer set to tint at 2 PM and clear at 6 PM handles most of the summer glare without manual intervention. Use a DIN-rail programmable timer in the panel, wired in series with the manual override so the occupant can still force a tint or clear if needed. An astronomical clock—one that adjusts on/off times based on sunrise and sunset—adds refinement but requires annual DST updates if your timer doesn't auto-adjust. We've installed this on a Sadashivanagar penthouse with a south-west corner study; the glass tints ten minutes before peak solar altitude and clears at dusk, tracked to the day of the year.

Lux sensor and building-management integration

A roof-mounted lux sensor can trigger the tint cycle when exterior illuminance exceeds a threshold—typically 50,000 lux, roughly midday in April. Wire the sensor output to a relay input on the transformer module. This is useful for facades that see variable shading from adjacent buildings or trees; the glass responds to actual light levels, not clock time. If the villa has a KNX or Crestron home-automation backbone, the electrochromic transformer can accept a 0–10V analogue input for proportional dimming. Coordinate the control voltage and protocol with the automation integrator early—retrofit integration after handover usually means a panel re-wire.

For projects that also use switchable PDLC partitions in conference or media rooms, keep the electrochromic and PDLC circuits separate. PDLC needs continuous AC (typically 48V AC at 50 Hz) and switches in under a second; electrochromic needs pulsed DC and takes minutes. Mixing them on a single control bus causes timing conflicts and confuses the occupant—one switch that sometimes responds instantly and sometimes takes five minutes reads as a fault.

The five-minute tint cycle: what happens and why it matters

Electrochromic glass does not snap dark. The tint ramps over four to six minutes, depending on pane size and ambient temperature. At 25°C, a 2.5 m × 1.8 m lite typically completes the cycle in five minutes; at 35°C—common on a Bangalore terrace in May—the same pane may tint in four minutes because ionic mobility in the coating increases with temperature. Below 15°C, the cycle can stretch to seven minutes. This thermal sensitivity means you cannot spec a fixed tint-time in the control logic; allow a ten-minute window in any automated sequence to ensure full transition before the next event.

The glass holds its tinted state without continuous power. Once the ions have migrated, a brief maintenance pulse every few hours keeps them in place; total hold-mode power is under 0.5W per square metre. If mains power fails, the glass slowly drifts back to clear over 24–72 hours as ions relax. This is a feature, not a bug—it means the facade fails safe (clear) rather than staying dark and blocking natural light during an outage. For projects where you need guaranteed tint during a power cut, add a small UPS to the transformer; a 300VA unit will hold a 10 m² facade in tint for eight hours.

Intermediate tint states are stable and repeatable. You can stop the cycle at any point—say, 50% tint—and the glass will hold that exact transmittance until you issue the next command. This makes electrochromic glass well-suited to facades where you want nuanced daylight control, not just on/off. We've used this on a Whitefield villa library: the client runs the tint to 30% in the morning for reduced contrast on the reading table, then to 80% tint in the afternoon when the sun is direct. The control is a rotary dimmer knob, same logic as a lighting dimmer, wired to a 0–10V input on the transformer.

Warranty, service access, and what voids coverage

Electrochromic glass typically carries a ten-year warranty on the coating and five years on the transformer and control electronics. The warranty requires that the installation follow the manufacturer's wiring spec to the letter—wrong voltage, under-gauge cable, or excessive ripple all void coverage. Keep the electrical test certificates (insulation resistance, earth continuity, voltage at the glass terminals under load) and the commissioning report in the project O&M manual. If the glass develops uneven tint or a stuck pixel, the manufacturer will ask for those documents before dispatching a technician.

Service access is critical. The junction box behind the frame head must remain accessible without removing the glass. If you've built a false ceiling or a pelmet that covers the box, leave a hinged or removable panel. We've had to cut open a gypsum soffit on an Indiranagar penthouse to reach a failed connector; the client was not pleased. Similarly, the transformer in the panel must be on a dedicated breaker, clearly labelled, so that the electrician can isolate it without killing power to the rest of the floor.

Do not apply aftermarket window film over electrochromic glass. The film changes the thermal load on the coating and can cause delamination or colour shift. If the client wants additional UV rejection, specify a laminate interlayer with UV-absorbing PVB during the glass make-up, not a stick-on film later. And do not use abrasive cleaners or scrapers on the interior surface—the electrochromic coating is on surface 2 or 3 of the laminate, and aggressive cleaning can scratch through the protective layer. A microfiber cloth and distilled water are enough; for Cauvery hard-water spots, a 5% citric-acid solution once a month.

Questions we get asked

Can I retrofit electrochromic glass into an existing window frame?

Possible, but rarely practical. Electrochromic lites are made-to-order laminates with specific edge-seal and bus-bar geometry; you cannot cut them on site. If the existing frame is aluminium or steel and dimensionally sound, you can re-glaze with new electrochromic lites, but you'll still need to chase the wall for DC cable back to the panel. Most architects find it cleaner to replace the entire window assembly—frame, glass, and seals—so that edge clearances and thermal breaks are optimised for the new lite thickness, which is typically 28–32 mm for a laminated electrochromic unit versus 18–24 mm for standard double-glazing.

What happens if the transformer fails mid-tint?

The glass freezes at whatever tint level it had reached when power was lost, then slowly drifts back to clear over 24–72 hours. It will not stay dark indefinitely. Replace the transformer, re-commission the system, and the glass resumes normal operation. No permanent damage to the coating, provided the failure was a clean power loss and not a voltage spike. If lightning or a surge caused the failure, check the glass terminals for burn marks and test the coating with a multimeter before re-energising—short-circuit damage can propagate through the bus bar and kill the entire lite.

How do I spec electrochromic glass on a shop drawing?

Call out the lite build-up in the window schedule: "6mm clear toughened + electrochromic interlayer + 6mm clear toughened laminate, 28mm total, with integrated bus bar and weatherproof terminal pigtail, 300mm length." Note the DC supply voltage (e.g. "48V DC ±5%, max ripple 3%") and the cable spec ("2-core 1.5mm² shielded, run in dedicated 25mm PVC conduit from panel to frame head junction box"). Reference the control logic in the electrical notes: "Electrochromic tint controlled by momentary push-button at location E-12 and programmable timer in DB-1, with manual override." Include a detail of the junction-box location and a cable-routing isometric if the run is complex. The glass supplier will issue a separate wiring diagram; append it to the electrical package so the contractor has one consolidated set of drawings.

Can electrochromic glass be used overhead, like a skylight?

Yes, with caveats. The glass itself is a laminate and can be toughened or heat-strengthened for overhead use, same as any skylight lite. The challenge is cable routing—you need a weather-sealed conduit run up the roof structure to the skylight frame, and the junction box must be IP65-rated and accessible from below or via a roof hatch. Thermal cycling is more extreme on a roof (60°C+ in summer) so the tint-cycle time will vary more than on a vertical facade. We've installed electrochromic skylights on two Bangalore projects, both with motorised vents for stack ventilation; the glass tints to reduce solar gain and the vent opens to exhaust hot air, controlled by the same building-management system. For simpler overhead privacy or glare control, consider our PDLC switchable skylight spec, which toggles opaque-to-clear in under a second and uses standard AC wiring.

What is the power consumption over a year for a 10 m² electrochromic facade?

Assume two full tint cycles per day (clear → dark in the afternoon, dark → clear in the evening), five minutes each, at 10W per m² during the cycle. That's 10 m² × 10W × (10 minutes / 60) × 2 cycles = 33 Wh per day during active tinting. Add hold-mode power: 10 m² × 0.5W × 23.67 hours (the rest of the day) = 118 Wh per day. Total ~150 Wh per day, or 55 kWh per year. For comparison, a single 1.5-ton inverter AC in the same room will draw 1000–1200 kWh per year. The electrochromic glass reduces cooling load by blocking solar heat, so the net energy balance is strongly positive—we've measured 15–20% reduction in afternoon AC runtime on west-facing rooms in Koramangala and Jayanagar projects, which more than offsets the glass's own consumption.

Commission your electrochromic facade

Electrochromic glass is bespoke by nature—every lite is made to site dimensions, every electrical run is drawn to the as-built panel location, every control sequence is tuned to the room's orientation and use. If you're specifying a villa facade in Devanahalli, Sarjapur, or Whitefield and need the wiring package, transformer spec, or a tint-cycle demonstration, talk to the atelier. We'll send the shop drawing, the cable schedule, and a commissioning checklist that keeps your electrical contractor and your client aligned from rough-in to handover.