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

Stand in a Hennur penthouse at 3 p.m. on a June afternoon, watch the SmartGlass panel above the living room begin to tint, and you'll see it: a half-second pause at 40% opacity before the relay fires and the tint deepens to 70%. The homeowner calls it lag. The electrician calls it normal. The architect, standing between them, needs to know the difference—because that pause isn't a defect. It's a conduit problem, and it was specified three months earlier on a shop drawing nobody read carefully.

This post is for architects and designers managing SmartGlass retrofits in Bangalore's granite-belt housing stock, where load-bearing partitions and existing structural beams make in-wall conduit routing impossible. We'll walk through why relay hesitation happens, how to read an electrical shop drawing, and what to tell your client at handover.

The relay lives outside the wall when the wall won't cooperate

SmartGlass dimming systems—whether our Notte clear-to-blackout panels or Privato privacy glass—require a 24V DC relay to switch the polycarbonate layer between transparent and opaque. That relay sits in a junction box, fed by a low-voltage wire that runs from the control switch (usually at the room entry) to the glass panel. In new construction, that wire runs inside a 16mm conduit buried in the slab or behind the drywall before the partition is framed. In retrofit work, especially in Bangalore's older residential stock around Hennur, Kalyan Nagar, and Sadashivanagar, you don't have that luxury.

A load-bearing partition—the kind that holds up the floor above—cannot be chased. You cannot cut a 50mm groove into a 230mm brick wall that's carrying 40 tonnes of structure. The electrician knows this. The architect should know this before the site dimensions are locked. What happens instead is the relay box gets surface-mounted on the outside face of the partition, the low-voltage wire runs in surface-mounted conduit along the wall, and the signal path gains 4 to 6 metres of extra wire length compared to a new-build specification.

Why conduit length matters to the dimming cycle

Electromagnetic induction and the 2-second hesitation

A SmartGlass relay operates on a simple principle: when the control switch sends a 24V signal down the low-voltage wire, the relay's solenoid energises, flips a contact, and power flows to the glass. In new construction with conduit buried in concrete, the wire runs 1.5 to 2 metres. In a retrofit surface-mount installation, that same wire may run 5 to 7 metres—around door frames, over skirting boards, across the width of a partition to reach the nearest structural point where the junction box can be mounted without cutting into load-bearing masonry.

Longer wire = higher capacitance in the circuit = a measurable delay in the relay response. Not a failure. A delay. Typically 1.5 to 2.5 seconds between the moment the occupant presses the dimming switch and the moment the glass begins to change opacity. On a 10mm laminated panel, this translates to a visual pause: you'll see the tint hold at 40% for a full second, then deepen. It's not uniform. It looks like hesitation.

This is not a manufacturing defect. It is not a fault in the glass. It is electrical physics, and it is predictable. An electrician who has fitted SmartGlass before will specify a 1.5mm² cable in a 16mm conduit with a 24V relay rated for high-capacitance circuits. A first-time retrofit electrician will use standard 1mm² wire and wonder why the response feels sluggish.

Site dimensions and the conduit routing decision

The moment the architect realises a partition is load-bearing, the electrical shop drawing changes. Instead of a buried conduit, you're specifying surface-mounted PVC or steel conduit, colour-matched to the wall finish (usually white or grey in Bangalore residential work). The conduit routing must be planned on the RCP—reflected ceiling plan—and on the elevation, because it will be visible. It will run from the control switch, typically 1.2 metres up from the finished floor, down to the skirting, along the skirting to the nearest corner, up the corner to the junction box mounted 2.1 metres high on the partition face.

That routing is 6 to 8 metres of wire. Compare it to a new build where the wire runs 1.8 metres inside the slab. The difference in capacitance is real, and it will show up in the dimming response time.

Reading the electrical shop drawing: what to look for

When the electrical contractor submits a shop drawing for SmartGlass dimming, the architect should check three things:

1. Conduit type and gauge. It should specify PVC or steel conduit, 16mm diameter minimum, with a note about whether it's surface-mounted or buried. If the note says "buried in partition"—and the partition is load-bearing—flag it immediately. That drawing will not be buildable.
2. Wire specification. Look for "1.5mm² shielded twisted pair" or "1.5mm² control cable". If it says "1mm² standard twin", and the conduit run is longer than 3 metres, ask the electrical engineer to upgrade. The capacitance matters.
3. Relay location and mounting height. The junction box should be mounted no higher than 2.2 metres on the partition face (reachable for maintenance) and no lower than 1.8 metres (above typical skirting height). If it's mounted on the opposite side of the partition from the glass panel, the wire run doubles, and so does the lag.

If the drawing doesn't specify these details, send it back. A vague electrical drawing for SmartGlass is a site problem waiting to happen.

Hennur and the retrofit standard: what the site teaches you

Hennur's residential stock—the tower blocks and villas built between 2005 and 2015—sits on granite bedrock. The foundations are deep, the partitions are solid brick, and the structural engineer will not permit chasing. Retrofit SmartGlass installations here are now common enough that electricians have learned the surface-mount standard. The first time an architect specifies buried conduit in a load-bearing wall, the site supervisor will stop work and ask for a revised drawing. That's the moment you want to be ready with the surface-mount specification already in hand.

In Koramangala and Indiranagar, where older bungalows are being renovated into multi-unit apartments, the same constraint applies. The load-bearing walls are non-negotiable. The conduit runs surface-mounted. The relay hesitation becomes part of the handover brief.

Handover and occupant training: what to tell the client

The hesitation is not a defect, but it is a change in user experience compared to new construction. At handover, the architect or interior designer should walk the occupant through the dimming cycle and explain it explicitly: "When you press the dimming switch, the glass will begin to change opacity after approximately 2 seconds. This is normal. It happens because the electrical signal travels a longer distance through the wiring than it would in a newly built home. The glass itself is functioning perfectly; the relay is responding normally."

Most occupants accept this explanation without complaint. Some ask whether it can be faster. The answer is yes, but only by shortening the conduit run—which means moving the relay junction box closer to the control switch, or moving the switch closer to the glass panel. Either option requires re-routing conduit and re-testing the circuit. It's a retrofit change order, and it costs money. Once the occupant understands that the 2-second delay is the trade-off for not cutting into a load-bearing wall, they usually accept it.

Document this in the handover manual. Note the relay type, the wire gauge, the conduit length, and the expected response time. If a future occupant or maintenance contractor calls it a fault, you have a paper trail showing it was specified as-built.

Specifying surface-mount conduit: the material choice

Surface-mounted conduit in Bangalore residential work comes in three materials: rigid PVC, flexible PVC (Conduit Pipe), and mild-steel with enamel finish. PVC is the standard because it's cost-effective, doesn't rust in Bangalore's monsoon humidity (June to September), and can be painted to match the wall. Steel conduit is specified when the wall finish is polished concrete or when the architect wants a more industrial aesthetic. Flexible conduit is rarely used for SmartGlass circuits because the longer flex path increases capacitance further.

The conduit should be colour-matched to the wall finish in the shop drawing. If the wall is off-white, specify white PVC conduit. If it's grey, specify grey. This isn't decoration—it's specification discipline. A mismatched conduit is a visible defect on handover, and the contractor will be asked to repaint it.

Joint tolerance and the relay box mounting

The junction box (typically 150mm × 100mm × 75mm deep) must be mounted flush to the partition face with a tolerance of ±2mm. If it's proud of the wall by more than 3mm, it catches the eye. If it's recessed, the conduit connection becomes awkward. The electrician should use a spirit level and a straightedge during installation. The architect should inspect it before the wall is painted.

The conduit entry into the box should be sealed with a grommet to prevent dust and moisture ingress. In a retrofit, this detail is often overlooked because the box is mounted after the partition is finished. Specify it explicitly: "All conduit entries to the relay junction box shall be fitted with 16mm rubber grommets, sealed with silicone sealant."

Questions we get asked

Can we bury the conduit in the slab instead of surface-mounting it?

Not in a retrofit where the slab is already finished. In new construction, yes—the conduit is laid before the concrete is poured. In retrofit work, you'd need to cut a chase in the finished floor, which damages the slab and creates a moisture path. Surface-mount is the only practical option.

Does the 2-second delay happen with all SmartGlass systems, or just ours?

It's physics, not brand-specific. Any PDLC or electrochromic glass system running on a 24V relay will experience capacitance-induced delay if the control wire is longer than 3 metres. The magnitude varies slightly depending on the relay circuit design, but the phenomenon is universal. A contractor who promises zero lag on a surface-mounted retrofit is either lying or doesn't understand the circuit.

What if we move the control switch closer to the glass panel?

That reduces the wire run, which reduces capacitance and improves response time. It's a valid design choice, but it changes the user experience. If the switch is now 5 metres away from the room entry, occupants will find it inconvenient. The trade-off is worth discussing with the client before the electrical drawing is finalised.

Can we use a higher-voltage relay to speed up the response?

No. The glass panel is rated for 24V DC. Using a higher voltage will damage the PDLC layer. The relay voltage is fixed. The only variables are wire gauge, conduit type, and circuit length.

What happens if the relay fails in a retrofit installation?

The glass stays in whatever tint state it was in when the relay failed—usually transparent. Replacement is straightforward: the electrician disconnects the old relay box, mounts a new one in the same location, and reconnects the wiring. No new conduit is needed. The whole job takes 2 to 3 hours. We recommend keeping a spare relay on site during the first year after handover, especially in monsoon season when humidity can stress electrical contacts.

Commissioning a retrofit SmartGlass installation

If you're specifying SmartGlass for a retrofit project in Bangalore, start with the structural plan. Identify load-bearing partitions, mark them on the electrical RCP, and flag them for surface-mounted conduit routing. Brief your electrical engineer on the wire gauge and relay type before the shop drawing is issued. Review the drawing for conduit length and relay location. At site, inspect the conduit installation before the wall is finished, and document the relay response time in the handover manual.

Talk to the atelier about your project specifics—site dimensions, wall finishes, occupant expectations—and we'll help you spec the right relay and conduit configuration for a retrofit that performs like it was designed, not like it was bolted on as an afterthought.