Somfy Sonesse 28 Motor Wired Into a 3-Blind Roman Set on a Bay Reveal

A splayed bay with three Roman blinds is not one job. It is three jobs that have to end up looking like one, and the Sonesse 28 mains motor makes that harder than a cord set because you cannot fudge alignment after the fact. Each 28 tube runs off its own motor head, so you are committing to three drilled bracket positions before any fabric goes up. Get the reveal depth wrong on the centre pane and the outer two mock the error back at you every time the light hits.

Start with the reveal, because everything downstream inherits its mistakes. A bay reveal is almost never square. Measure the depth at the top left, top right, and dead centre of each of the three openings. On a 1990s brick bay I measured last autumn the depths ran 68mm, 71mm, and 64mm across a single centre pane. That 7mm spread decides whether a face-fix bracket clears the tube or fouls the plaster line.

Reveal depth is the number that kills the job

The Sonesse 28 head plus its universal bracket wants roughly 55mm of clear projection before the fabric even enters the picture. Add the roll diameter of the finished Roman on its cassette and you are frequently past 75mm at full stack. On a shallow reveal that pushes the whole assembly proud of the plaster, and the outer blinds on a splayed bay then sit at an angle that reads as crooked even when it is dead level.

Measure each opening at three heights, not one. Reveals bow. The plaster at cill level is often 3mm to 6mm tighter than at the head because of how the render was floated. Take the smallest of the three readings per opening and work to that, because a bracket that fits the top and fouls the bottom is still a bracket that fouls.

The splay angle is the second trap. On a canted bay the two outer panes meet the centre at something near 135 degrees, but the actual figure drifts pane to pane. If you set all three tubes to the same projection off the plaster, the fabric edges on the mitre lines will overlap or gap. I set the centre blind first, get its face flush, then bring the outer two in to match the visible front plane, not the reveal depth. The eye reads the front line, never the depth.

Brackets and the order you hang them

Sonesse 28 ships with a snap bracket that takes the motor head on one end and an idle pin on the other. For three blinds that is six brackets, and the failure mode is drilling all six before test-fitting a single tube. Fit the two centre brackets, drop the centre tube in, level it with a 600mm spirit level laid along the top of the tube, and only then transfer marks outward.

On a masonry reveal use a 6mm masonry bit and brown plugs, but check for the old timber sub-frame first. Plenty of bay reveals have a hardwood liner behind 8mm of plaster, and a masonry plug spinning in timber gives you a bracket that pulls out the first time the Roman stacks under its own weight. Tap the reveal with the drill off. A dull thud is timber, a sharp tick is brick. Timber wants a 4mm pilot and a 40mm screw straight in, no plug.

The idle-end bracket on the Sonesse 28 has a small amount of lateral float built in, which you use to square the tube against a slightly out-of-parallel reveal. Do not use it up on the first blind. Keep the float centred so the outer blinds, which will need it more, still have somewhere to go. On the 68mm-to-64mm reveal I mentioned, the two outer idle brackets ended up using nearly all their float to keep the fabric hanging plumb.

Sonesse 28 wiring, three motors, one switch drop

The Sonesse 28 is a mains motor, 230V, and each one draws its own live-neutral-earth plus the two control cores if you are running the wired dry-contact version rather than RTS radio. Three motors off one bay means three feeds back to a junction, and the cleanest route is a single 4-gang junction box in the pelmet void with the switched live commoned across all three if you want them to move together.

Colour discipline matters here because Somfy wired motors use a specific scheme and it is not the UK domestic one. Brown is not always live in the motor tail. The Sonesse wired flex runs live, neutral, earth, plus a common and a control core, and the two control cores are the ones that set direction on a momentary switch. Cross them and the blind runs up when you press down. Test one motor fully, both directions, before you common the other two, because a wiring fault multiplied across three heads is three times the fault-finding.

If you are grouping the three onto a single wall switch or a Situo channel, run each motor into a Somfy interface and address them together, but leave the physical common wiring in place as a fallback. Radio grouping fails silently when a wall switch dies. A hard-wired common still moves the blinds. Leave a 300mm service loop on each motor tail in the pelmet so a future motor swap does not mean re-terminating at the junction box under a stapled pelmet board.

The limit setting on the 28 is done at the motor head with the setting button and the switch, running the fabric to the closed position and pressing to confirm, then to the open position and confirming again. On three blinds set them one at a time and mark the closed limit against a level line struck across all three reveals with a laser. If you set limits by eye per blind, the three bottom bars will not line up across the bay, and on Roman fabric that misalignment is brutally visible.

The centre pane governs everything

Set the centre blind perfectly and let the outer two chase it. If the centre is 2mm off level, you carry that error twice outward and the bay looks drunk. The centre pane is the only reference the eye trusts on a symmetrical bay.

Blackout lining and the stack you did not plan for

A Roman with blackout lining stacks fatter than a standard lined one, and on a motorised bay that changes the projection math you did during the reveal measure. Three-pass blackout lining adds real bulk to each fold, and when the blind is fully raised the stacked bundle can sit 90mm to 110mm deep off the tube on a longer drop. That stack has to clear the reveal return on a shallow bay or it presses against the plaster and the motor stalls against the obstruction.

The Sonesse 28 has enough torque to keep pulling into a stall, and that is the quiet way you damage fabric. A blind that fouls its own stack against the reveal will crush the top folds over a few weeks and you get a permanent crease line. On the 64mm-deep centre pane the blackout Roman stacked to 95mm and would have jammed. The fix was a spacer bracket bringing the tube 20mm off the plaster, which throws the whole projection out again and sends you back to reconciling the front plane across all three blinds.

Blackout lining also holds condensation on a north-facing bay. The lining traps a cold layer against the glass side and on winter mornings the bottom fold can come up damp. That is not a wiring fault and no motor setting fixes it, but it changes whether you fit the fabric tight to the glass or leave an air gap at the cill, which in turn changes your drop measurement by 10mm to 15mm.

Levelling three bottom bars across a splay

Strike one laser line across all three reveals at the intended closed height and set every motor limit to that line, ignoring the individual cill heights. Bay cills are rarely level with each other. If you reference each blind to its own cill, the three bottom bars step up and down across the bay and it looks like a mistake even though every blind is individually correct.

The unresolved part is the mitre gap between adjacent Roman fabrics on the splay. Two flat fabric panels meeting at a 135-degree cant will always show a hairline of reveal between them at the fold edges, and no motor calibration closes that gap. Whether you accept the sliver of visible plaster or over-width the outer blinds to bridge it is the one decision on this job that the wiring diagram will never answer for you.