Specifying SmartGlass for a Whitefield home-office partition: wiring, dimming and the shop drawing

The brief called for a 2.7 m × 1.2 m partition between a guest bedroom and a home office in a Whitefield villa—transparent when the client needs the space to feel open, frosted when video calls require privacy. The contractor had already poured the slab, the electrician had pulled conduit to a single-gang box on the partition centreline, and the interior designer asked for a dimmer. That last request changes the entire electrical specification. Switchable privacy glass—PDLC film laminated between two lites—runs on low-voltage DC, which means a transformer, a controller, and if dimming is required, a compatible dimmer module rated for capacitive loads. None of that fits in a single-gang box, and none of it belongs in the partition itself. This is the kind of coordination that separates a clean handover from a site argument three weeks before the client moves in.

What switchable glass actually needs from your electrical RCP

PDLC—polymer-dispersed liquid crystal—film switches from translucent to clear when voltage is applied. The film itself draws between 3 and 5 watts per square metre, so a typical 3 m² residential partition consumes roughly 15 watts at 48 VDC. That power comes from a step-down transformer hidden in a false ceiling or service void, not at the switch location. Your RCP should show three elements: a 230 VAC supply line to the transformer location, a low-voltage cable run from the transformer to the glass edge, and a control cable from the wall switch back to the transformer. The switch itself is a momentary push-button or a capacitive-touch plate, not a mechanical rocker. If the client wants dimming—gradual transition from frosted to clear—you specify a PWM dimmer module that sits alongside the transformer, and the control cable carries a 0–10 V analogue signal or a DALI bus, depending on the home-automation backbone.

Most coordination failures happen because the electrician treats the glass like a light fixture and pulls only a switch-leg. By the time the glass arrives on site, the false ceiling is closed, and there is no path for the low-voltage cable to the glass edge. Mark the transformer location on your RCP—typically within 10 metres of the partition to keep voltage drop below 2%—and call out the cable spec: 2-core shielded 1.5 mm² for the DC supply, 4-core shielded 0.75 mm² if you are running DALI. If the project uses a centralised lighting-control system, the transformer can be wired into a DIN-rail relay module in the electrical room, and the glass becomes just another zone on the touch panel.

Tolerances and the structural opening

Switchable glass is a laminate—two lites of toughened glass with PDLC film and two layers of PVB in between—so it is thicker and heavier than monolithic glass of the same nominal size. A typical residential specification is 5 mm + 5 mm with film, giving a finished thickness of 10.76 mm including the interlayer. That extra half-millimetre matters when you are detailing an aluminium channel or a patch-fitting. If your shop drawing shows a 12 mm glazing pocket and you assume the glass will be 10 mm, the fitter arrives on site with a 10.76 mm lite and discovers there is no clearance for setting blocks. Spec the pocket at 13 mm minimum, with 2 mm tolerance on each edge for alignment.

The structural opening itself should be 6 mm wider and taller than the finished glass dimension—3 mm perimeter tolerance is standard for residential work, but if the partition is site-cut and the walls are out of plumb by more than 4 mm over the height, you will need to scribe the glass or accept a visible gap at one edge. We template every opening before cutting, because as-built dimensions in a Whitefield villa are rarely what the architect drew. If the partition is load-bearing or if there is a concrete lintel above, confirm that the header can carry the glass weight—10.76 mm laminate weighs approximately 26 kg/m², so a 3 m² panel is 78 kg, and that load transfers through the top channel or the patch-fittings to the structure. A 50 mm × 25 mm aluminium box-section header is adequate for spans up to 1.5 m; beyond that, specify a steel RHS with a powder-coat finish or a deeper aluminium extrusion.

Joint lines and electrical termination

The low-voltage cable enters the glass at one edge, typically the bottom or side rail, through a 6 mm hole drilled 50 mm from the corner. The cable is soldered to a copper bus-bar laminated into the PDLC film, and the connection is sealed with a silicone gasket to keep moisture out. That joint is not field-serviceable—if the connection fails, the entire panel must be returned to the atelier. Your shop drawing should show the cable-entry point and specify which edge is accessible after installation. If the partition is floor-to-ceiling with no removable base channel, the cable must enter from a side edge, and that edge must remain accessible for future maintenance. If the partition is frameless—glass held by top and bottom channels only—the cable enters through the bottom edge, and the channel must have a service access panel or a removable cover strip. Mark this on your section detail, because contractors will close the channel with silicone and make the termination inaccessible.

Dimming: what works and what does not

Standard wall dimmers—the kind designed for incandescent or LED lighting—do not work with PDLC glass. The film requires a constant DC voltage to stay clear, and a phase-cut dimmer chops the AC waveform before it reaches the transformer, which causes the film to flicker or fail to switch at all. If your client wants gradual dimming, specify a PWM dimmer module rated for capacitive loads, installed between the transformer and the glass. The module takes a 0–10 V control signal from a compatible wall dimmer or a home-automation system and modulates the DC output to the film. The result is a smooth transition from frosted to clear over 2 to 5 seconds, depending on the ramp rate you program.

Most residential projects in Bangalore use a Lutron or Schneider lighting-control system, and both manufacturers offer 0–10 V dimmer modules that work with PDLC transformers. The wall switch is a low-voltage keypad or a capacitive touch-plate, and the control cable runs back to a central processor in the electrical room. If the project does not have a home-automation system, you can specify a standalone PWM dimmer with a rotary knob or a slider, but the client will need to understand that the control is analogue—there is no scene recall or integration with voice assistants. For projects where dimming is not critical, a simple on-off switch is the most reliable option, and it eliminates an entire layer of electrical coordination.

Transformer placement and heat dissipation

The transformer is a 230 VAC to 48 VDC step-down unit, typically a sealed metal enclosure about 150 mm × 100 mm × 50 mm. It generates heat—enough that it cannot be buried in insulation or enclosed in a sealed void without ventilation. Your RCP should show the transformer mounted on a DIN rail in a ventilated service box, or strapped to a ceiling joist in a false ceiling with at least 100 mm clearance above and below. If the false ceiling is gypsum board on a metal grid, the transformer can sit on the grid itself, but it must be mechanically fastened—double-sided tape will fail within six months due to thermal cycling. If the project has a centralised electrical room, mount the transformer there and run the low-voltage cable through the ceiling plenum to the partition. The cable can share a conduit with other low-voltage circuits—DALI, Ethernet, speaker wire—but keep it separate from mains AC to avoid interference.

What the shop drawing must show

A complete shop drawing for switchable glass includes five views: elevation with finished dimensions and joint lines, plan section showing the channel profile and setting-block locations, head and sill details showing the cable-entry point, an electrical schematic with transformer location and cable routing, and a material call-out specifying glass thickness, film type, and edge finish. The elevation should mark the cable-entry point and the switch location, so the electrician knows where to pull conduit. The plan section should show the glazing pocket depth, the setting-block thickness, and the clearance for thermal expansion—PDLC laminates expand and contract with temperature at roughly the same rate as monolithic glass, but the interlayer can creep under load, so the pocket must allow 1 mm of vertical movement over a 2.4 m height.

The electrical schematic is often the missing piece. It should show the transformer, the dimmer module if specified, the low-voltage cable run with wire gauge and shielding, the control cable from the wall switch, and the mains supply to the transformer. If the project uses a home-automation system, the schematic should show the control-bus connection—DALI, KNX, or 0–10 V—and the device address if the system requires it. This level of detail prevents the electrician from improvising on site, which is how you end up with a mechanical dimmer wired in series with a PDLC transformer and a client who cannot turn the glass off.

Site dimensions and as-built verification

We do not cut switchable glass until we have verified site dimensions with a laser measure and a plumb-bob. Whitefield villas—especially the ones built in the post-2015 tech-corridor boom—often have walls that are out of square by 8 to 10 mm over a 3 m span, and floors that are out of level by 6 mm. If your architectural drawing shows a 2700 mm × 1200 mm partition and the site opening measures 2706 mm × 1197 mm with one corner 9 mm out of plumb, the glass will not fit without scribing or shimming. The shop drawing should include a site-verification checklist: opening width at top, middle, and bottom; opening height at left, right, and centre; diagonal measurements to check for square; and plumb tolerance at each corner. If the partition is between two fixed walls, measure the opening after the walls are plastered and painted, not after the block-work. Plaster thickness varies by 3 to 5 mm depending on the mason, and that variance shows up as a gap at the glass edge.

Switchable glass in other residential applications

The same electrical and structural principles apply to switchable bathroom privacy glass, where the partition is often smaller but the humidity is higher. Bathroom installations require an IP65-rated transformer and a moisture-sealed cable termination, and the glass edge must be protected from direct water contact—PDLC film is laminated between two lites, but the edge seal is not waterproof in the same way a sealed IGU is. If the partition is in a shower enclosure, specify a 10 mm offset from the showerhead spray zone, and detail a silicone edge seal at the sill to prevent water from wicking into the laminate. For larger installations—conference rooms that disappear or sky-rated PDLC overhead in a double-height living room—the electrical load scales linearly with area, so a 10 m² overhead skylight will draw 50 watts and require a transformer rated for at least 75 watts to allow headroom for inrush current. The same dimming and control principles apply, but the structural coordination becomes more complex because the glass is overhead and the cable must be routed through the roof deck or a concealed chase.

Questions we get asked

Can I use a standard LED dimmer with switchable glass?

No. PDLC film requires a constant DC voltage to stay clear, and a phase-cut dimmer designed for LED lighting will cause the film to flicker or fail to switch. If you want dimming, specify a PWM dimmer module rated for capacitive loads, installed between the transformer and the glass. The module takes a 0–10 V control signal from a compatible wall dimmer or a home-automation system.

What happens if the power fails—does the glass stay clear or frosted?

PDLC film is frosted in its unpowered state. When the power fails, the glass reverts to translucent within 2 to 3 seconds. If your client requires privacy during a power outage, specify a UPS for the transformer, or use a different technology—electrochromic glass stays in its last state when power is removed, but it is slower to switch and significantly more expensive.

How much clearance do I need around the glass edge for the cable termination?

The low-voltage cable enters the glass through a 6 mm hole drilled 50 mm from the corner, and the connection requires at least 30 mm of accessible space behind the glass edge. If the partition is frameless, the cable enters through the bottom edge, and the base channel must have a removable cover strip or a service access panel. If the partition is framed, the cable can enter through a side edge, but that edge must remain accessible—do not silicone the channel closed.

Can I retrofit switchable film onto existing glass?

Yes, but only if the glass is accessible from both sides and the surface is perfectly clean and flat. Retrofit smart film is applied with a wet adhesive and requires a dust-free environment and a skilled fitter. The film is thinner than laminated PDLC—about 0.4 mm—so it is more prone to bubbles and edge-lifting if the substrate is not prepared correctly. For new construction, we recommend laminated PDLC because the film is protected between two lites and the edge seal is factory-controlled.

What is the lead time for a custom switchable partition?

Four to five weeks from shop-drawing approval to site delivery. The glass is cut and toughened locally, then sent to the lamination facility where the PDLC film is applied. The laminate is autoclaved, edge-polished, and tested before it leaves the atelier. If the project is on a faster schedule, we can sometimes compress the timeline to three weeks, but that depends on the lamination queue and the availability of the film in the correct size.

If you are specifying switchable glass for a Bangalore residential project and need a shop drawing that coordinates electrical, structural, and glazing details to the millimetre, talk to the atelier. We template, fabricate, wire, and fit every piece by hand, and we work directly with your electrician to make sure the transformer, dimmer, and control cables are in place before the glass arrives on site.