A multi-unit inductor system (301, 401) comprising: a first inductor assembly (300A, 400A) including: a first coil including: a spirally wound first metal foil; a second metal foil spirally co-wound in face-to-face electrical contact with the first metal foil to form a multilayer conductor; and an electrical insulator sheet spirally co-wound with the first and second metal foils; and a second inductor assembly (300B, 400B) including: a second coil including: a spirally wound third metal foil; a fourth metal foil spirally co-wound in face-to-face electrical contact with the third metal foil to form a second multilayer conductor; and a second electrical insulator sheet spirally co-wound with the third and fourth metal foils; wherein the first coil is electrically connected to the second coil; and characterised in that: the first coil has a first coil longitudinal axis (A-A); the second coil has a second coil longitudinal axis; each of the first and second inductor assemblies includes: a first terminal bus bar connected to the coil thereof and projecting outwardly from an axial end of the inductor assembly; and a second terminal bus bar connected to the coil thereof and projecting outwardly from the axial end of the inductor assembly; wherein the first and second inductor assemblies are positioned side-by-side and the first terminal bus bar of the second inductor assembly is electrically connected to the second terminal bus bar of the first inductor assembly. a first inductor assembly (300A, 400A) including: a first coil including: a spirally wound first metal foil; a second metal foil spirally co-wound in face-to-face electrical contact with the first metal foil to form a multilayer conductor; and an electrical insulator sheet spirally co-wound with the first and second metal foils; and a spirally wound first metal foil; a second metal foil spirally co-wound in face-to-face electrical contact with the first metal foil to form a multilayer conductor; and an electrical insulator sheet spirally co-wound with the first and second metal foils; and a second inductor assembly (300B, 400B) including: a second coil including: a spirally wound third metal foil; a fourth metal foil spirally co-wound in face-to-face electrical contact with the third metal foil to form a second multilayer conductor; and a second electrical insulator sheet spirally co-wound with the third and fourth metal foils; a spirally wound third metal foil; a fourth metal foil spirally co-wound in face-to-face electrical contact with the third metal foil to form a second multilayer conductor; and a second electrical insulator sheet spirally co-wound with the third and fourth metal foils; wherein the first coil is electrically connected to the second coil; and characterised in that: the first coil has a first coil longitudinal axis (A-A); the second coil has a second coil longitudinal axis; each of the first and second inductor assemblies includes: a first terminal bus bar connected to the coil thereof and projecting outwardly from an axial end of the inductor assembly; and a second terminal bus bar connected to the coil thereof and projecting outwardly from the axial end of the inductor assembly; wherein the first and second inductor assemblies are positioned side-by-side and the first terminal bus bar of the second inductor assembly is electrically connected to the second terminal bus bar of the first inductor assembly. the first coil has a first coil longitudinal axis (A-A); the second coil has a second coil longitudinal axis; each of the first and second inductor assemblies includes: a first terminal bus bar connected to the coil thereof and projecting outwardly from an axial end of the inductor assembly; and a second terminal bus bar connected to the coil thereof and projecting outwardly from the axial end of the inductor assembly; a first terminal bus bar connected to the coil thereof and projecting outwardly from an axial end of the inductor assembly; and a second terminal bus bar connected to the coil thereof and projecting outwardly from the axial end of the inductor assembly; wherein the first and second inductor assemblies are positioned side-by-side and the first terminal bus bar of the second inductor assembly is electrically connected to the second terminal bus bar of the first inductor assembly.