Short answer: A Somfy SDN shade system runs on two cable types. Each motor home-runs to an isolated port on an SDN PowerConnect panel, up to 240 ft. Keypads, hubs and interfaces ride a Cat 5e bus wired as one line, with stubs of 10 m or less, a 120 ohm terminator at each end and no more than 255 nodes.
SDN jobs rarely fail at the motor. They fail at the wire. A bus split into a star, a missing terminator or a home run 60 ft past its limit shows up the week you commission, with the GC waiting and the ceiling closed. This guide gives you the numbers Somfy publishes, in the order you need them on a commercial shade project, and a spec package you can drop into the submittal.
Free spec package
Somfy SDN commercial shade system spec package
- System riser with cable types and run limits
- Wiring schedule you can paste into a submittal
- Editable 3-part guide specification
- Bill of materials with Somfy reference numbers
Two cable systems, one network
Somfy Digital Network (SDN) carries RS485 data and 24V DC power. On a current Somfy system the motors and the control devices sit on separate wiring, and confusing the two causes most field problems.
Motors connect to the Somfy SDN PowerConnect Surface-Mount Panel (1871026). Each of its 10 isolated motor ports feeds one motor with power and data on a single run of up to 240 ft. An electrician lands 120V AC on the panel, rated 7.2 A maximum, and the panel puts out Class 2 24V DC on every port. Somfy lists this panel as the replacement for all earlier SDN motor power panels.
Control devices connect to the SDN bus: keypads, the SDN RTS receiver, a Data Hub and the IP interface. The panel adds two isolated device ports of its own, each good for one device up to 200 ft away.
The bus rules, in numbers
Somfy's SDN Bus Wiring Guide sets these limits. Print them on the riser and hold the low-voltage crew to them.
SDN bus rules
- Up to 255 nodes on one SDN bus. An active junction counts as one node.
- Cat 5e or higher, terminated to T568B: pins 1 and 2 carry SDN data, 4 and 5 carry +24V, 7 and 8 carry ground.
- Stubs from the bus to a device: 10 m (about 33 ft) maximum.
- 120 ohm terminator at both ends of the bus.
- Bus topology only. No star, no ring.
- Bus power supply: 24V DC, plus or minus 10%, 1 A maximum, with at least 9V DC left at every powered device.
- Total bus length with a 24V supply: 1,000 m (about 3,280 ft) maximum, split across the two legs from the supply.
The 1,000 m ceiling assumes light loads spread along the run. Somfy's worked example puts 240 mA of devices on one leg for 500 m and 200 mA on the other for 500 m. Bunch the devices at the far ends and the allowed length drops: Somfy's concentrated example tops out at 740 m. Count milliamps before you count feet.
Motor runs: cable, gauge and plenum
Somfy builds a dedicated motor cable for SDN. The SDN Low-Voltage Power and Data Cable, Non-Plenum (9020126) carries a 14 AWG power pair rated 300V plus the RS485 data pair, and Somfy rates it to 240 ft on a motor port. Return-air ceilings take the plenum-rated version (9020127). The PowerConnect enclosure carries a UL 2043 plenum rating, so the panel and the cable can both live above an open-return ceiling.
Spec the cable by part number. Generic thermostat wire saves a few hundred dollars and costs you the warranty conversation later. Somfy states that its own power supplies keep the UL listing intact on low-voltage systems, and the same discipline applies to the cable that feeds them.
Picking the motor for each opening
Two RS485 motors cover most commercial roller shades on SDN. The Somfy Sonesse 30 RS485 24V DC (1241144) delivers 2 Nm at 25 rpm in a tube as small as 1.13 in, the fit for offices and classrooms with standard window widths. The Somfy Sonesse ULTRA 50 RS485 (1134022) sets torque anywhere from 2 to 6 Nm and speed from 10 to 25 rpm, on a 1.85 in minimum tube, for wide boardroom and lecture-hall shades where quiet operation sells the job.
Size torque from the shade, not the opening. Fabric weight, hem bar and tube all add load, and a motor run at its ceiling wears early. Our rule: pick the next size up when the math lands within 20% of the rated torque.
Head end: bus power, Data Hub and the IP bridge
The PowerConnect panel powers its own two device ports. Add a Somfy SDN Data Hub V2 (1870951) or any other bus-powered device and Somfy calls for a separate bus supply, the Somfy Bus and Sensor Station Power Supply (1822440). The Data Hub gives five device ports with stubs up to 200 ft and can power three keypads or one RTS receiver.
For Control4, Crestron or Savant, the Somfy Connect UAI Plus (1870272) commissions and integrates up to 250 SDN motors over IP through the Somfy Synergy API. It supports Sonesse 30 RS485, Sonesse 50 ULTRA RS485 and Glydea ULTRA, and on Control4 it reports motor position on OS 2.9 or higher. One UAI Plus usually replaces a pile of serial drivers and the programming hours that come with them.
Commissioning without a callback
Set limits and read addresses at the shade with the Somfy RS485 Setting Tool (9017142). Group, name and back up the system from a Windows laptop through the Somfy USB to RS485 Adapter (9015260) and Somfy's Set pro software. Before you leave the panel, run each port from the UP, STOP, DOWN and SEQ buttons on its face. A port that will not move today is a wiring fix. Next month it becomes a truck roll.
Hand the owner three things at closeout: the address list, the configuration backup and the as-built riser. The spec package below has a checklist for all of it.
Order list for a 10-shade floor
One PowerConnect panel, ten RS485 motors sized per opening, ten motor runs of 9020126 or 9020127, Cat 5e for the bus, two terminators, one UAI Plus if a control system joins, and the setting tool or USB adapter for commissioning. Add a Data Hub and a bus supply once keypads outgrow the two device ports. Thirty shades means three panels chained on Bus In and Bus Out.
Take the spec package to your submittal
Somfy SDN commercial shade system spec package
- System riser with cable types and run limits
- Wiring schedule you can paste into a submittal
- Editable 3-part guide specification
- Bill of materials with Somfy reference numbers
FAQ
How many motors can one Somfy SDN bus handle?
Somfy allows up to 255 nodes on one SDN bus. Motors on a current system connect to SDN PowerConnect panels, ten isolated motor ports per panel, and panels chain on the bus. For control-system integration, one UAI Plus commissions and integrates up to 250 SDN motors over IP.
What cable does Somfy SDN use?
Motor runs use Somfy's SDN low-voltage power and data cable: 9020126 for open areas or 9020127 for plenum spaces, rated to 240 ft per motor port. The device bus uses Cat 5e or higher terminated to T568B, with stubs of 10 m or less and a 120 ohm terminator at each end.
Can I wire an SDN bus as a star?
No. Somfy specifies bus topology only. Run the bus as one continuous line, branch to each device with a stub of 10 m or less, and place a 120 ohm terminator at both ends. Star splits cause reflections and intermittent faults that show up during commissioning.
Does the PowerConnect panel need a separate power supply for the bus?
The panel powers its own two device ports. Once a Data Hub or another bus-powered device joins the bus, Somfy calls for a separate bus supply. The Somfy Bus and Sensor Station Power Supply (1822440) fills that role.
Sources: Somfy SDN Bus Wiring Guide; Somfy SDN PowerConnect Surface-Mount Panel product page, spec sheet (2025.09.10) and instructions (2025.09.09); Somfy Low Voltage Databook; Somfy Connect UAI Plus product page (1870272); Somfy SDN Data Hub V2 product page (1870951); Somfy Control4 integration page.
Ryan Towns writes the Somfy Integrator Guides for ShadeMotorsDirect, an authorized Somfy distributor. Questions on a spec or a retrofit: 859-414-6872 or colin@shademotorsdirect.com, 8:00 AM - 7:30 PM ET.
