Switching module with automatic switching to call for audio door entry system with 3 speech units, for use with power supply units 0931, 931A, 0936, 938A and 0931/0CT, option of multiple connection to several 0839/303 switching modules and a maximum of 9 speech units, installation on DIN rail (60715 TH35), occupies 8 modules size 17.5 mm
