Abstract: A primary enclosure for electric power meters includes at least one shelf for supporting an instrument transformer. Slide mounts are mounted to the interior of the enclosure and to the shelf for slidably supporting the shelf for movement between a first use position in which the shelf and the transformer carried by the shelf are contained entirely within the interior of the enclosure and a second extended position wherein the shelf extends at least partially through an opening in a wall of the enclosure for servicing of the transformer The shelf can include shelf brackets attachable to the slide mounts and a transformer adapter plate to which the transformer is mounted prior to attaching the adapter plate to the adapter shelf to the shelf brackets.