SmartGlass wiring through a partition: why the relay placement breaks the dimming spec when conduit runs through a structural beam

A home-office partition in Devanahalli arrived at the electrical coordination stage with a problem that looked minor on the RCP but broke the dimming spec in the shop drawing. The architect had specified a partition with SmartGlass that dims, routed the control conduit through the structural beam to reach the panel, and left the relay placement to the electrician. By the time the first site dimension was taken, the relay was 4.2 metres from the glass—well beyond the manufacturer's maximum run length for signal integrity without a booster.

This is not a rare scenario. Bangalore's post-2010 residential boom has produced homes where electrical panels sit at the perimeter and structural grids leave few options for vertical routing. The problem compounds when SmartGlass dimming is added: the control signal is low-voltage DC, sensitive to cable length, voltage drop, and electromagnetic noise in shared conduit. Relay placement is not a site decision—it is a specification that must be locked into the shop drawing before the glass is commissioned.

Why relay placement matters for SmartGlass dimming

SmartGlass dimming operates on a control signal that travels from a wall switch or sensor to a relay, which then switches the mains voltage to the glass. The relay is the junction point. It sits between the low-voltage control circuit (typically 12V DC) and the high-voltage power circuit (230V AC in India). The distance from the relay to the glass affects signal quality and response time.

Manufacturer specs for most dimming systems specify a maximum cable run of 2.5 to 3 metres from relay to glass without signal degradation. Beyond that, voltage drop and capacitive coupling introduce lag, flicker, or complete loss of dimming control. A relay placed 4+ metres away requires either a booster (additional cost, additional component in the field), a larger gauge cable (conduit space, cost), or a repositioned relay (coordination with the electrical contractor and structural grid).

The relay itself is a small enclosure—roughly 120 × 80 × 60 mm—but its location determines the entire control architecture. If it sits at the main panel, the conduit run to the partition may be long. If it sits at the partition, the mains supply conduit must be longer, and the partition itself must have space for a secondary enclosure. Neither choice is free.

The Devanahalli case: conduit routing through the beam

The partition was a 2.4-metre-wide opening between a living room and a home office. The architect specified SmartGlass with manual dimming—a switch-controlled system where occupants could adjust transparency for privacy during calls. The electrical panel was located at the far end of the living room, roughly 6 metres horizontally from the partition, with the structural beam running perpendicular at 3.5 metres from the panel.

The electrician's first instinct was to run the control conduit vertically up to the beam, then horizontally through the beam's web (a common practice in Bangalore homes where the beam is the only available routing spine), then down to the partition. This path was 5.8 metres total, with the relay remaining at the main panel. The shop drawing for the glass specified a 3-metre maximum run from relay to dimming terminal on the glass. The discrepancy was caught only when the glass fabricator reviewed the electrical layout against the atelier's standard control schematic.

Structural coordination and the beam routing constraint

Bangalore homes built after 2005 typically use 300–400 mm deep RCC beams with conduit sleeves cast into the web during construction. Routing through the beam is standard practice, but it creates a bottleneck: the beam's location is fixed, and any conduit running through it must align with the original sleeve or require post-casting drilling—expensive and structurally risky. The electrician cannot simply reroute around the beam; the beam is the routing path.

In the Devanahalli case, the beam routing was the only viable path to avoid running conduit along the living-room ceiling (which would have been visible and conflicted with the plasterboard finish). But the beam routing forced the relay to stay at the main panel, which in turn forced the 5.8-metre run to the glass.

The shop drawing coordination: where the spec breaks

The atelier's shop drawing for SmartGlass dimming includes a control schematic that specifies relay location, cable gauge, and maximum run distance. This is not a suggestion—it is a performance requirement tied to the warranty. When the electrician's layout showed a 5.8-metre run, the schematic became unachievable without modification.

Three options emerged during the coordination meeting:

1. Install a secondary relay at the partition itself, fed by mains conduit from the main panel. This added cost (roughly 8,000–12,000 rupees for a small enclosure, breaker, and wiring), but reduced the control run to under 1.5 metres and restored the standard spec.
2. Upgrade the control cable to a larger gauge (2.5 mm² instead of 1.5 mm²) and add a signal booster relay. This cost more (15,000–18,000 rupees) and introduced an additional component in the field, increasing maintenance risk.
3. Reposition the main panel—not feasible in this case, as the panel location was set by the building's original design and the homeowner's preference for a central location.

The architect and electrician chose option 1: a secondary relay enclosure mounted inside the partition's utility cavity, fed by a 4 mm² mains conduit from the main panel. This approach kept the control run short, maintained the standard dimming spec, and required only one coordination change to the RCP—a note showing the secondary enclosure location and the mains conduit routing.

Specifying SmartGlass dimming: the coordination checklist

For architects and designers specifying SmartGlass with dimming on Bangalore projects, the relay placement decision must happen during the design phase, not on site. This requires early coordination between the architect, electrician, and glass atelier.

Before the shop drawing

Confirm the electrical panel location and the partition location on the RCP. Measure the horizontal and vertical distance between them. If the distance exceeds 3.5 metres, flag a relay coordination issue early. Discuss conduit routing with the electrician: will it run through beams, along the ceiling, or in walls? Identify any structural constraints that force a particular path.

The shop drawing phase

The glass atelier will provide a control schematic that shows relay location, cable runs, and switch placement. This schematic must be reviewed against the electrical layout. If the relay is at the main panel and the run to the glass exceeds 3 metres, decide on secondary relay placement or cable upgrades before the glass is fabricated. Any change after fabrication is costly and delays handover.

On-site verification

When the partition is ready for installation, the electrician must verify actual site dimensions. Measure from the relay terminal to the glass control terminal. If the measurement differs from the shop drawing by more than 0.5 metres, pause installation and confirm the spec is still met. Hard water in Bangalore (TDS 200–300 ppm from the Cauvery) does not affect electrical runs, but monsoon humidity (June–September) can introduce condensation in poorly sealed conduits—ensure all conduit entries are gasketed.

Common relay placement mistakes on Bangalore projects

Relay placed at the main panel without checking the run distance to the glass. This is the most common error. The electrician assumes the relay location is fixed and does not flag the distance issue until the glass arrives.

Conduit routed through the structural beam without confirming capacity. Bangalore's granite-belt construction often uses dense RCC with limited web space. Sharing a sleeve with power conduit can introduce electromagnetic interference into the control signal. Separate sleeves or shielded control cable are required.

Secondary relay enclosure specified but not sized for the partition cavity. A relay enclosure needs clearance for terminal connections and maintenance access. If the partition is 100 mm thick, a 120 mm enclosure will not fit. Coordination with the glass atelier confirms the exact enclosure dimensions before the partition is framed.

Control cable run through the same conduit as mains voltage without shielding. This is a code violation and a performance risk. Control cable must be shielded or run in a separate conduit if it shares a route with mains voltage.

Why this matters for privacy glass systems and beyond

SmartGlass dimming is most common in home offices and conference spaces, but the relay placement issue applies to any smart glass system—blackout glass, switchable privacy partitions, even projection-ready screens. Each system requires a control signal path, and each has a maximum run length beyond which performance degrades. The difference is that dimming failures are visible (flicker, lag, incomplete transparency change), while signal loss on other systems may go unnoticed until the warranty period has passed.

Bangalore architects working on residential and home-office projects in HSR Layout, Indiranagar, Koramangala, and the newer Devanahalli and Sarjapur Road developments are increasingly specifying smart glass for privacy and light control. The coordination challenge is the same across all of these micromarkets: electrical panels are rarely positioned for short control runs, structural beams create routing constraints, and relay placement is a design decision, not a site improvisation.

Questions we get asked

Can the relay be placed inside the partition itself without access from outside?

Yes, if the partition is designed with a utility cavity or service void. The relay enclosure must remain accessible for maintenance and troubleshooting, so it cannot be sealed inside the glass cavity itself. A 100–150 mm service cavity on one side of the partition (typically the side facing a corridor or utility space) is standard. The enclosure is then mounted to the partition frame, and the mains conduit enters from above or below.

What happens if the control cable run is longer than the spec after installation?

The dimming system will likely exhibit lag or flicker—the glass will respond to switch input with a 0.5–2 second delay, or the transparency change will be jerky rather than smooth. In extreme cases (runs over 6 metres), the relay may not receive the signal at all. The warranty does not cover performance issues caused by out-of-spec cable runs, so the homeowner is left with a non-functional dimming system and the cost of a secondary relay or cable upgrade.

Does Bangalore's hard water affect the electrical control system?

No. Hard water (Cauvery TDS 200–300 ppm) affects glass surface maintenance and mineral deposits on seals, but it does not degrade electrical signal. The concern is monsoon humidity (June–September) and condensation in unsealed conduits, which can cause corrosion on terminal connections. All conduit entries must be gasketed and sealed to prevent moisture ingress.

Can I upgrade the control cable gauge to avoid a secondary relay?

In some cases, yes—upgrading from 1.5 mm² to 2.5 mm² cable reduces voltage drop and improves signal integrity over longer runs. However, this is not a substitute for the manufacturer's maximum run spec. A 2.5 mm² cable may extend the viable run by 0.5–1 metre, but it does not eliminate the need for a booster or secondary relay on very long runs (over 4.5 metres). The electrician and glass atelier must confirm the upgrade is acceptable before the glass is fabricated.

How early in the design phase should I coordinate relay placement?

During the RCP and electrical layout stage—before the partition is detailed in the shop drawing. Once the electrical panel location and the partition location are fixed on the RCP, measure the distance and confirm with the glass atelier that the control run is achievable. This takes 10 minutes and prevents delays and cost overruns during installation.

Commissioning your SmartGlass partition

Relay placement is one coordination detail among many, but it is the one most often overlooked because it sits at the boundary between electrical and glass trades. The atelier can help architects and designers navigate this decision early—talk to the team at Vetrova to review your RCP, confirm relay placement, and lock the control schematic into the shop drawing before the glass is commissioned.