An electrical connector system comprising a first electrical connector for terminating a first plurality of electrical conductors and a second electrical connector configured to mate with the first electrical connector and for terminating a second plurality of electrical conductors, the first electrical connector comprising a first metal shell and a first terminal subassembly that is held by the first metal shell and that includes a first group of terminals configured to be electrically connected to the first plurality of electrical conductors, and characterised in that the second electrical connector comprises: a second terminal subassembly having a second group of terminals configured to be electrically connected to the second plurality of electrical conductors, the second terminal subassembly having an insulator holding the second group of terminals, the second terminal subassembly having a mating interface where mating surfaces of mating ends of the second group of terminals mate with the first group of terminals at a mating interface of the first terminal subassembly; and a second metal shell holding the second terminal subassembly, wherein the second metal shell has the cross-sectional shape of an oval, the second metal shell comprising a terminating segment and a tunnel that extends outward from the terminating segment and has an open end for receiving the first metal shell when the first and second electrical connectors are mated, wherein the insulator of the second terminal subassembly comprises a platform, the mating ends of the second group of terminals positioned on a terminal side of the platform, the mating surfaces of the second group of terminals being arranged along the terminal side of the platform such that the mating interface of the second terminal subassembly extends on the platform, wherein the mating interface of the second terminal subassembly is approximately flat, the tunnel surrounding the platform, wherein the tunnel is spaced apart from the platform along at least three sides of the platform, and wherein the first metal shell includes a sealing ring configured to sealingly engage with the interior surface of the tunnel to seal the open end of the tunnel when the first and second electrical connectors are mated. a second terminal subassembly having a second group of terminals configured to be electrically connected to the second plurality of electrical conductors, the second terminal subassembly having an insulator holding the second group of terminals, the second terminal subassembly having a mating interface where mating surfaces of mating ends of the second group of terminals mate with the first group of terminals at a mating interface of the first terminal subassembly; and a second metal shell holding the second terminal subassembly, wherein the second metal shell has the cross-sectional shape of an oval, the second metal shell comprising a terminating segment and a tunnel that extends outward from the terminating segment and has an open end for receiving the first metal shell when the first and second electrical connectors are mated, wherein the insulator of the second terminal subassembly comprises a platform, the mating ends of the second group of terminals positioned on a terminal side of the platform, the mating surfaces of the second group of terminals being arranged along the terminal side of the platform such that the mating interface of the second terminal subassembly extends on the platform, wherein the mating interface of the second terminal subassembly is approximately flat, the tunnel surrounding the platform, wherein the tunnel is spaced apart from the platform along at least three sides of the platform, and wherein the first metal shell includes a sealing ring configured to sealingly engage with the interior surface of the tunnel to seal the open end of the tunnel when the first and second electrical connectors are mated.