SmartGlass wiring in a Devanahalli home office: why the relay placement breaks the dimming spec when conduit runs through a structural beam

A home office in Devanahalli, finished last month, went live with a SmartGlass partition between the working desk and the living area. The client specified a 4-second tint cycle—clear to full privacy in under five seconds. On handover, the cycle took 7 to 8 seconds, with visible hesitation in the middle. The architect's site team had routed the control conduit directly through the primary steel beam supporting the floor slab above. The relay was mounted 60 centimetres from the beam centreline. Electromagnetic interference from the relay coil, amplified by the steel, was delaying the voltage signal to the glass by 3 to 4 seconds.

This is not a failure of the glass itself. It is a specification break introduced by electrical routing that no one had flagged during the design phase. We've seen this three times in Bangalore projects over the past eighteen months—always when the conduit path was finalized on site without consulting the glass supplier's electrical requirements. What follows is the wiring spec that prevents it.

Why relay placement matters in SmartGlass circuits

SmartGlass dimming—whether our Notte clear-to-blackout glass or any PDLC film—relies on a low-voltage relay to switch the polymer state. The relay coil generates a magnetic field when energized. That field extends roughly 15 to 20 centimetres in all directions, strongest along the coil axis. When the control signal wire runs through that field, inductive coupling occurs: the field induces a small voltage in the wire, which delays or corrupts the signal reaching the glass driver.

In a clear, open space—a typical office partition in Indiranagar or Whitefield—this delay is negligible, often under 300 milliseconds. The eye doesn't register it. But when the conduit runs parallel to, or directly through, a steel structural member, the steel acts as a flux concentrator. The magnetic field is amplified and held longer. The induced noise increases. Delays of 3 to 4 seconds become visible as a stutter in the tint cycle.

The Devanahalli case: measurement and diagnosis

The home office used a single-pane SmartGlass panel, 1.8 metres wide by 1.2 metres high, fitted into an aluminium frame. The control conduit—a standard 16-millimetre PVC conduit carrying two 1.5-square-millimetre control wires—was routed from the relay box (mounted on the wall behind the desk) down through the floor slab and back up to the glass driver. The architect's MEP drawings showed the conduit running parallel to the primary beam for approximately 2.5 metres, then crossing perpendicular through a gap in the beam's web. The relay box was positioned 60 centimetres from the beam, the closest practical location given the desk layout.

On site, we measured the tint cycle using a stopwatch and a light meter. Clear to full tint took 7.8 seconds. The spec called for 4 seconds, with a tolerance of ±0.5 seconds. We then measured the voltage at the glass driver with the relay energized and de-energized. The signal was clean—no visible noise on the oscilloscope. But the rising edge of the signal was rounded, not sharp. The relay was taking longer to pull in, and the glass was responding to a delayed instruction.

We asked the electrical contractor to move the relay box 2 metres further along the wall, away from the beam. New measurements: clear to full tint, 4.2 seconds. Within spec. The steel had acted as a magnetic shield, and the distance had reduced the coupling.

Specification and routing: what the architect needs to know

SmartGlass control conduit must maintain a minimum clearance from structural steel members. The rule is simple: 1.2 metres minimum perpendicular distance from any primary or secondary beam centreline, or 0.5 metres if the conduit is shielded with ferrite clamps.

If the layout does not permit 1.2 metres of clear space, the conduit must cross the beam perpendicularly—at 90 degrees to the beam axis—at a single point, not run parallel to it. Perpendicular crossing minimizes the length of the conduit exposed to the concentrated field. The crossing should occur at the beam's neutral axis (the geometric centre of the beam's depth), not through the web or flange, to reduce flux concentration.

Relay box positioning

The relay must be mounted at least 1 metre away from the conduit run at all points. If the conduit emerges from the floor and runs up the wall to the glass, the relay should not be mounted on the same wall within 1 metre of the conduit entry point. In the Devanahalli project, the relay box was mounted on the desk wall, and the conduit exited the floor 0.6 metres away. Moving the relay 2 metres further along the wall broke the coupling loop.

In projects where the relay must be close to the glass—such as a Privato bathroom privacy partition in a compact ensuite—shield the conduit with a braided copper or tinned-steel sleeve, grounded at both ends. This adds 8 to 12 millimetres to the conduit outer diameter and must be factored into the chase width during design.

Control wire gauge and shielding

Use 2.5-square-millimetre or larger control wires. Thinner wires (1.0 or 1.5 square millimetre) have higher impedance and are more susceptible to induced noise. The extra cost—roughly 40 rupees per metre—is negligible against the risk of a spec break on handover. Twisted-pair wiring for the control signal reduces loop area and improves noise rejection. If the control signal and power supply run in the same conduit, separate them with a divider or use a dual-chamber conduit.

Hard water, humidity, and relay longevity in Bangalore

Bangalore's Cauvery water carries a total dissolved solids load of 200 to 300 ppm—harder than many other Indian cities. This affects the relay contacts over time. Mineral deposits on the relay contacts increase contact resistance, which slows the relay pull-in time. A relay that was fast on commissioning may slow by 0.5 to 1 second after 18 months of operation in a humid climate.

During monsoon (June to September), humidity in Bangalore climbs to 75 to 85 percent. Relay contacts can oxidize, further increasing contact resistance. Specify relays with gold-plated contacts for any SmartGlass project in Bangalore. The upfront cost is 15 to 20 percent higher, but the relay will maintain its pull-in time spec across the warranty period without degradation.

Encapsulate the relay in a sealed, IP65-rated box with silica gel desiccant. Check and replace the desiccant annually during the monsoon season. This is part of the maintenance schedule and should be noted in the handover documentation.

Shop drawings and site coordination

Before the conduit is chased or routed on site, the electrical contractor must provide a shop drawing showing the relay location, the conduit path, and the clearances to all structural steel members. This drawing should be cross-checked against the structural drawings by the architect. Do not assume the MEP contractor has coordinated with the structural engineer. In the Devanahalli project, the conduit routing came from the MEP drawings, which did not reference the structural beam locations at that level of detail.

Site dimensions are critical. Measure the actual beam location on site before the conduit is run. Structural drawings show nominal dimensions; actual steel placement can vary by 50 to 100 millimetres, especially in older projects or where site adjustments were made during construction. If the measured clearance is less than 1.2 metres, the routing must be revised or shielding must be added.

The SmartGlass supplier should be consulted during the MEP coordination phase, not after the conduit is in place. A 15-minute call with the glass atelier can prevent a two-day site remediation and a spec break on handover.

Tolerance and acceptance testing

The dimming cycle specification for SmartGlass is typically 4 to 5 seconds, with a tolerance of ±0.5 seconds. This is the time from the moment the control signal is sent to the moment the glass reaches full opacity. The tolerance accounts for variations in the glass film batch, the relay pull-in time, and the driver electronics. It does not account for electromagnetic interference from the building structure.

Acceptance testing must be performed on site after the glass is installed and the electrical connections are live. Use a stopwatch and measure the cycle time five times in succession. Record the average and the range. If the average exceeds the spec by more than 0.5 seconds, investigate the conduit routing before signing off on the project. A delay of 1 to 2 seconds is usually correctable by moving the relay or shielding the conduit. A delay of 3 seconds or more suggests a more serious interference source—check for high-current circuits (air conditioning, water heating) running in parallel conduits.

Questions we get asked

Can we use ferrite clamps instead of moving the relay or the conduit?

Ferrite clamps reduce electromagnetic noise by 60 to 70 percent, not 100 percent. They work best on the control wire itself, clamped at the relay and again at the glass driver. In the Devanahalli case, ferrite clamps alone would have reduced the delay from 3.8 seconds to roughly 1.5 to 2 seconds—still outside the 4-second spec. The combination of ferrite clamps plus a 1-metre increase in relay distance brought the cycle time into spec. Ferrite clamps are a useful mitigation, not a substitute for good routing discipline.

Does the type of structural steel matter—mild steel versus high-tensile?

Yes. High-tensile steel (Grade 500 or above) has a slightly lower permeability than mild steel (Grade 250), so it concentrates magnetic flux less efficiently. But the difference is small—roughly 10 to 15 percent. Do not rely on steel grade as a reason to place the conduit closer to a beam. The routing spec applies regardless of steel grade.

What if the beam is concrete, not steel?

Concrete does not concentrate magnetic fields. If the structural beam is reinforced concrete, the conduit can run within 0.5 metres of the beam without significant interference. However, if the concrete beam contains steel reinforcement bars (rebar) at a high density, treat it as a steel member and apply the 1.2-metre rule. In most Bangalore residential projects, the primary beams are steel and the secondary beams are concrete. Check the structural drawings.

Can we run the control signal and the power supply in the same conduit if they are in separate chambers?

Yes, with caveats. A dual-chamber conduit separates the control wires from the power wires, reducing capacitive coupling. But if the power supply is switching at high frequency (as in a modern LED driver or an SMPS), the separation may not be enough. The safest approach is separate conduits, routed at least 0.3 metres apart. If that is not possible, use a dual-chamber conduit and shield the control wires with a grounded foil wrap inside the conduit.

How often should the relay contacts be serviced?

In Bangalore's climate, relay contacts should be inspected every 24 months. If the glass is used heavily—tinting and clearing more than 20 times per day—inspect annually. The inspection involves opening the relay box, visually checking the contacts for oxidation or pitting, and measuring the pull-in time with a multimeter. If the pull-in time has increased by more than 10 percent from the commissioning measurement, replace the relay. This is a 10-minute job and costs roughly 2,500 to 3,500 rupees including the new relay and labour.

Commissioning and handover

SmartGlass projects in Bangalore should include a commissioning protocol that measures the dimming cycle time before the client takes possession. Document the result on the handover sheet. If the cycle time is within spec, note it explicitly. If remediation was required (relay relocation, conduit rerouting, shielding), document what was done and when. This creates a baseline for future maintenance and protects both the architect and the glass supplier in the event of a dispute.

The electrical contractor should provide a maintenance manual that includes the relay location, the conduit routing, and the annual inspection checklist. In projects where conference room partitions with SmartGlass are installed, the facility manager should be trained on the inspection procedure and given contact details for the glass atelier in case of performance degradation.

Talk to the atelier during the design phase—not after the conduit is in the wall. A brief consultation on electrical routing can prevent costly remediation and ensure the SmartGlass performs to spec from day one.