A feedthrough assembly comprising: at least one conductive line; and a feedthrough element configured to isolate a first portion of the feedthrough assembly from a second portion of the assembly, wherein the feedthrough element comprises: a housing having a bore extending therethrough; a seal pre-loader and a seal-pre-loader housing; a first seal formed by a first portion of the at least one conductive line in contact with a mating surface of the bore of the housing; a second seal formed by contact between a stacked arrangement of sealing elements with a second portion of the at least one conductive line and an inner surface of the housing; and a member in contact between the pre-loader housing and a third portion of the at least one conductive line and being configured to apply a first pre-loading force in the axial direction of the conductive line to promote sealing of at least the first seal prior to deployment in an operating environment, characterised in that the third portion of the at least one conductive line has a maximum outer diameter greater than a maximum outer diameter of the first portion and greater than an outer diameter of the second portion of the at least one conductive line to allow the first pre-loading force to be applied. at least one conductive line; and a feedthrough element configured to isolate a first portion of the feedthrough assembly from a second portion of the assembly, wherein the feedthrough element comprises: a housing having a bore extending therethrough; a seal pre-loader and a seal-pre-loader housing; a first seal formed by a first portion of the at least one conductive line in contact with a mating surface of the bore of the housing; a second seal formed by contact between a stacked arrangement of sealing elements with a second portion of the at least one conductive line and an inner surface of the housing; and a member in contact between the pre-loader housing and a third portion of the at least one conductive line and being configured to apply a first pre-loading force in the axial direction of the conductive line to promote sealing of at least the first seal prior to deployment in an operating environment, characterised in that the third portion of the at least one conductive line has a maximum outer diameter greater than a maximum outer diameter of the first portion and greater than an outer diameter of the second portion of the at least one conductive line to allow the first pre-loading force to be applied. a housing having a bore extending therethrough; a seal pre-loader and a seal-pre-loader housing; a first seal formed by a first portion of the at least one conductive line in contact with a mating surface of the bore of the housing; a second seal formed by contact between a stacked arrangement of sealing elements with a second portion of the at least one conductive line and an inner surface of the housing; and a member in contact between the pre-loader housing and a third portion of the at least one conductive line and being configured to apply a first pre-loading force in the axial direction of the conductive line to promote sealing of at least the first seal prior to deployment in an operating environment, characterised in that the third portion of the at least one conductive line has a maximum outer diameter greater than a maximum outer diameter of the first portion and greater than an outer diameter of the second portion of the at least one conductive line to allow the first pre-loading force to be applied.