An installation box for insertion through a hole in a wall or wall plate having dimensions adapted to conform to the outer circumference of a side wall of the installation box, the wall or wall plate having a front side and a back side, the installation box comprising a side wall having an edge defining a box opening, the installation box further comprising: a support member for supporting the installation box on a front side of a wall at the edge of the box opening, wherein the support member comprises a coupling portion (32, 36) coupling the support member to the side wall of the installation box, and a support portion connected to the coupling portion (32, 36); and wherein the coupling portion (32, 36) is configured to allow the support member to have a first position relative to the installation box in which the support portion is within an outer circumference of the edge of the side wall, and a second position in which the support portion extends beyond the outer circumference of the edge of the side wall, wherein the support member is coupled to the side wall at an interior side thereof; characterised in that: the coupling portion (32, 36) is configured to allow the support member to have the first position relative to the installation box such that the installation box, with the box opening in a leading position, can be pulled, from the front side of the wall or wall plate, to move through the hole in the wall or wall plate from the back side of the wall or wall plate to the front side of the wall or wall plate; and the installation box comprises outwardly extending support arms configured to be displaced relative to the side wall by pulling them in the direction from the back side of the wall or wall plate to the front side of the wall or wall plate, to bring the support arms against the back side of the wall or wall plate. a support member for supporting the installation box on a front side of a wall at the edge of the box opening, wherein the support member comprises a coupling portion (32, 36) coupling the support member to the side wall of the installation box, and a support portion connected to the coupling portion (32, 36); and wherein the coupling portion (32, 36) is configured to allow the support member to have a first position relative to the installation box in which the support portion is within an outer circumference of the edge of the side wall, and a second position in which the support portion extends beyond the outer circumference of the edge of the side wall, wherein the support member is coupled to the side wall at an interior side thereof; characterised in that: the coupling portion (32, 36) is configured to allow the support member to have the first position relative to the installation box such that the installation box, with the box opening in a leading position, can be pulled, from the front side of the wall or wall plate, to move through the hole in the wall or wall plate from the back side of the wall or wall plate to the front side of the wall or wall plate; and the installation box comprises outwardly extending support arms configured to be displaced relative to the side wall by pulling them in the direction from the back side of the wall or wall plate to the front side of the wall or wall plate, to bring the support arms against the back side of the wall or wall plate. the coupling portion (32, 36) is configured to allow the support member to have the first position relative to the installation box such that the installation box, with the box opening in a leading position, can be pulled, from the front side of the wall or wall plate, to move through the hole in the wall or wall plate from the back side of the wall or wall plate to the front side of the wall or wall plate; and the installation box comprises outwardly extending support arms configured to be displaced relative to the side wall by pulling them in the direction from the back side of the wall or wall plate to the front side of the wall or wall plate, to bring the support arms against the back side of the wall or wall plate.