IEC 61754-20-100:2012 covers connectors with protective housings. The housing is defined as variant 4 in IEC 61076-3-106:2006. These connectors use a push-pull coupling mechanism. To connect the fibres inside the housing the LC interface is used as described in IEC 61754-20:2002. The fully assembled variants (connectors) described in this document incorporate fixed and free connectors.