Disclosed is a halogen-free, flame retardant thermoplastic resin composition based on polypropylene and one or more thermoplastic elastomers with an organic nitrogen- and/or phosphorus-based intumescent flame retardant comprising a piperazine component. The composition is processed easily to make a wire and cable sheath exhibiting a balance of high flame retardancy, good flexibility, high wet electrical resistance and excellent heat deformation properties, and which passes the VW-I flame retardancy test, the UL1581 heat deformation test at 150° C. and the wet electrical resistance test, and also exhibits good tensile and flexibility properties. Also disclosed is a wire and cable sheath made from the composition.