2-wire connection (neutral conductor not required) For switching lighting systems. For Busch-Comfort switch control element 6815-to-101. For Busch-Presence detector sensors 6813- to -102. Combinable with Universal slave insert 6440/05 U. Operation in 1gang 2way installations via push switch-unit for combination with flush-mounted units. Operation also possible via conventional push buttons (2020 US, 2021/6 UK).