<p>The system has an electrical installation device (1) that is provided with a unit base (2). The base is provided with an independent support (6) having an interface opening (4). The base without a frame-like support ring for the locking insertion is formed into the interface opening of the support. The two diametrically opposite side portions of locking elements (8) are provided for engaging locking edges of an opening (4a) of the interface opening. An independent claim is included for an installation apparatus for use with building services system.</p>
