An access control system for restricting access through a passageway, the access control system comprising: a shaft which is rotatable about a central axis, a barrier fixed to the shaft to rotate therewith, and a brake assembly for applying a braking force to the shaft, wherein the brake assembly comprises: a sun gear which is rotatable about the central axis of the shaft; a carrier and a ring gear, wherein one of the carrier or the ring gear is fixed against rotation and wherein the other of the carrier or the ring gear is connected to the shaft to rotate therewith; a plurality of planet gears rotatably connected to the carrier so as to permit rotation relative to the carrier, each planet gear being disposed between the sun gear and the ring gear and engaging with each of the sun gear and the ring gear; and an electromagnetic brake comprising an electromagnet and an armature, the armature being connected to or integral with the sun gear to rotate therewith, wherein at least one of the electromagnet or the armature is moveable upon energisation of the electromagnet between an operative position in which the electromagnet and the armature are in contact, such that the electromagnetic brake provides a braking force to the sun gear, and an inoperative position in which the electromagnet is spaced from the armature, such that the electromagnetic brake provides no braking force to the sun gear. a shaft which is rotatable about a central axis, a barrier fixed to the shaft to rotate therewith, and a brake assembly for applying a braking force to the shaft, wherein the brake assembly comprises: a sun gear which is rotatable about the central axis of the shaft; a carrier and a ring gear, wherein one of the carrier or the ring gear is fixed against rotation and wherein the other of the carrier or the ring gear is connected to the shaft to rotate therewith; a plurality of planet gears rotatably connected to the carrier so as to permit rotation relative to the carrier, each planet gear being disposed between the sun gear and the ring gear and engaging with each of the sun gear and the ring gear; and an electromagnetic brake comprising an electromagnet and an armature, the armature being connected to or integral with the sun gear to rotate therewith, wherein at least one of the electromagnet or the armature is moveable upon energisation of the electromagnet between an operative position in which the electromagnet and the armature are in contact, such that the electromagnetic brake provides a braking force to the sun gear, and an inoperative position in which the electromagnet is spaced from the armature, such that the electromagnetic brake provides no braking force to the sun gear. a sun gear which is rotatable about the central axis of the shaft; a carrier and a ring gear, wherein one of the carrier or the ring gear is fixed against rotation and wherein the other of the carrier or the ring gear is connected to the shaft to rotate therewith; a plurality of planet gears rotatably connected to the carrier so as to permit rotation relative to the carrier, each planet gear being disposed between the sun gear and the ring gear and engaging with each of the sun gear and the ring gear; and an electromagnetic brake comprising an electromagnet and an armature, the armature being connected to or integral with the sun gear to rotate therewith, wherein at least one of the electromagnet or the armature is moveable upon energisation of the electromagnet between an operative position in which the electromagnet and the armature are in contact, such that the electromagnetic brake provides a braking force to the sun gear, and an inoperative position in which the electromagnet is spaced from the armature, such that the electromagnetic brake provides no braking force to the sun gear.