The invention relates to a kit of parts comprising DC, low voltage system of an elongated track and a plug. The elongated track has a first and a second end and comprises an elongated slot formed by a central groove with at least one shielded lateral groove, both grooves lying in a plane P. Typically two electric conductors are accommodated in said at least one lateral groove. A connector portion of the plug having a connector cross section which matches with a cross section of the slot. Both said slot cross section and connector cross section are asymmetrical with respect to a plane Q extending over the length axis perpendicular to plane P, and at least one of the slot cross section and connector cross section is mirror symmetrical with respect to said plane P. The symmetric and asymmetric requirements posed on both the cross section of the elongated track and the connector portion of the plug ensure that the connector portion only being insertable into the first end in the axial direction and, after a rotation of 180° over its connector axis, only being insertable in the axial direction into the second end of said track, with maintenance of the correct polarity The invention further relates to a plug suitable for use in the kit of parts according to the invention.