Somfy 520R2 LT50 Wired Motor Torque and Tube Fit Guide

A 20 Nm tubular motor sits in the middle of the Somfy LT50 range, and plenty of awnings and rolling shutters land right there. Installers reach for the Somfy LT50 520R2 120V 4-Wire Motor when a 10 Nm head runs short on lift and a 30 Nm head costs more than the opening needs. The motor turns 20 Nm (177 in-lb) at 14 rpm on 120V AC power. Somfy fits it with a star head, a mechanical limit switch, and a 9.84 ft SJTW pigtail, which puts it under a maintained wall switch or a third-party relay.

Tube diameter decides whether the motor goes in at all. Somfy publishes a minimum internal tube diameter of 1.85 in for this reference. Measure the inside of your tube before you order.

Torque first, then tube diameter

Pick the torque from the weight of the curtain and the diameter of the finished roll. A rolling shutter with aluminum slats pulls more than a fabric awning across the same opening. Somfy rates the 520R2 at 20 Nm, one step up from the 10 Nm 510S2 and one step below the 30 Nm 530R2 in the same LT50 family. An installer who sizes a job to the top of a motor's rating gives up service life, so leave headroom on the number.

Speed changes the feel of a tall drop. The 520R2 runs 14 rpm, the slower of the two common LT50 speed grades. A 14 rpm head covers a 10 ft drop at an unhurried pace and holds heavier assemblies on the way back up. On a shutter that trade reads as the right one.

The 1.85 in minimum internal diameter rules out 1.5 in tubes outright. A 2 in round tube, a 2.5 in round tube and a 70 mm octagonal tube all clear it once you add the matching crown and drive set. Somfy measures that figure at the narrowest point inside the tube, so a seam weld or a rolled edge counts against you.

Awnings, rolling shutters, and the loads a 520R2 carries

Somfy publishes two applications for this reference: awnings and rolling shutters. Both hang outside, and the motor carries IP 44 protection for that duty along with a working range of -13 to 158 F. The 500 Series housing takes the weather that an exterior tube sees behind a fascia or inside a shutter box.

A retractable awning loads the tube as the fabric extends, and the arms add resistance of their own at full stretch. A rolling shutter hangs its whole slat weight on the tube from the first turn. Weigh the finished assembly, not the fabric or the slats alone. Add the end bar.

The wired control path suits a job where the switch position never moves and the wall stays open long enough to pull cable. Contractors on new construction and gut remodels run 4-conductor cable to each motor head and land it on a maintained switch, which keeps the control out of a battery or a radio budget. Somfy supports the same motor behind a relay card in a shutter panel, so a 520R2 can answer a building automation contact closure.

Verified specs for the Somfy LT50 520R2

Those figures come from Somfy's own product data for reference 1042055 and the 500 Series databook.

Crown, drive, and bracket fit for a star head

Three parts stand between the motor and a working shade: a crown that centers the motor inside the tube, a drive that transmits the turn to the tube wall, and a bracket that holds the head. Somfy sells the crown and drive as a matched pair for each tube profile, and you buy the pair that matches the tube you already have.

For a 2.5 in round tube, use the Somfy LT50 2.5" Round Crown and Drive Set (9012231). For a 70 mm octagonal shutter tube, the Somfy Octagonal LT50 70mm Crown and Drive Set (9012234) seats the same motor in the eight-sided profile that shutter boxes use across Europe and a good share of North American retrofits. Mixing a crown from one profile with a drive from another leaves the motor off center, and an off-center motor scrapes the tube on every cycle.

The head needs a plate cut for a star. The Somfy LT50 Star Head Motor Bracket (9410651) accepts the star profile on this motor and bolts to the box or the wall. A round-head plate will not hold this head, so match the plate to the star.

Wiring a standard 4-wire LT50

Somfy ships the 520R2 with a 9.84 ft SJTW pigtail carrying four conductors. Two of them take the up and down commands from the switch, one returns as neutral, and one bonds the motor to ground, which the Class I rating requires. Check the conductor colors against the wiring diagram in the 500 Series databook for the unit in your hand before you make up the connections.

Never energize both direction conductors at once. A maintained switch rated for motor duty interlocks the two directions by design, and a relay card does the same in a panel. A run that outreaches the 9.84 ft pigtail takes the Somfy SJTW 4C Cable 10 ft (9018345), and the whole run stays at the same conductor count. Splice inside a box, never inside the tube.

Setting the mechanical limits

The 520R2 carries a mechanical limit switch with a 46-turn capacity, which counts the turns of the tube between the open stop and the closed stop. An installer sets each stop at the motor head and runs the shade through a full cycle to confirm both ends. Mechanical limits hold their setting through a power cut, since nothing in the head depends on stored electronics.

Count your turns before you commit to the motor. Divide the finished drop by the circumference of the loaded roll and compare the answer against 46. A deep rolling shutter on a 2 in tube climbs through turns faster than the same drop on a 2.5 in tube, and a job that needs more than 46 turns needs a different limit scheme.

Leave the thermal protection alone in your planning. Somfy rates the 520R2 for 5 minutes of continuous run with a trip at 284 F, which covers a residential cycle many times over. Repeated back-to-back cycles during commissioning can warm the motor enough to pause it, and the head resumes once it cools.

Shade Motors Direct stocks the Somfy LT50 520R2 120V 4-Wire Motor (1042055) as a genuine Somfy unit under the 5-year factory warranty. Order the crown and drive set for your tube profile in the same cart, add the star head bracket, and measure the run to the junction box so you know whether the 9.84 ft pigtail reaches on its own.

Frequently asked questions

What tube size does the Somfy 520R2 need?

Somfy publishes a minimum internal tube diameter of 1.85 in for reference 1042055. A 2 in or 2.5 in round tube clears that, as does a 70 mm octagonal shutter tube. Measure the narrowest point inside the tube, since a seam weld reduces the clear diameter. A 1.5 in tube will not take this motor.

How much weight will 20 Nm lift?

Torque converts to lifted weight through the radius of the loaded roll, so the same 20 Nm raises more on a small roll than on a large one. Somfy rates the 520R2 at 20 Nm (177 in-lb) at 14 rpm for awning and rolling shutter duty. Size from the finished assembly weight and roll diameter, and keep headroom under the rating.

Which control works with a standard 4-wire motor?

A maintained wall switch rated for motor duty drives the 520R2 over its 4-conductor SJTW pigtail, and a relay card in a shutter panel does the same job for building automation. The motor holds no radio receiver, so an RTS remote will not operate it. Wire the control in and interlock the two directions.

Can the limits be reset after installation?

Yes. The mechanical limit switch on the 520R2 adjusts at the motor head, and an installer can move either stop after the shade hangs. Capacity runs to 46 turns of the tube between stops. Mechanical limits survive a power outage with the settings intact, which keeps a shutter in place after a storm.

Shade Motors Direct is an authorized source for genuine Somfy motorized window shade, blind, and drapery parts.