A fully coupled 2D/axisymmetric model of opposed-flow flame spread over insulated electrical wire is developed and solved numerically. The gas-phase combustion model includes the full Navier-Stokes momentum equations along with conservation equations of mass, energy, and species. The solid phase model consists of continuity and energy equations whose solution provides boundary conditions for the gas phase. In this study, ETFE insulated copper wire is considered. The inner core has a diameter of 0.5 mm, and the insulation thickness is 0.15 mm. Two modeling approaches are considered for the insulation, in one the insulation regresses as it pyrolyses leading to metallic core being exposed to flame and in second the insulation pyrolyses but does not regress (represents a charring insulation). The role of heat conduction in axial and radial directions in the wire is investigated in both normal gravity and microgravity environments. Axial heat transport by conduction in copper core upstream in the preheat region plays a crucial role (1) by reducing heat loss from insulation to the copper core by radial conduction as in non-regressing insulation and (2) by providing additional heating of the insulator by metal core as in regressing insulation. The role of axial conduction by copper core is more significant in 0 g. The flame spread rate variation with insulator themal conductivity have opposite trends in 1 g and 0 g owing to the role of axial conduction in the copper core. Novelty and significance statement This work presents the first fully coupled numerical model involving gas phase flame interacting with regressing insulation over metal core is developed to simulate flame spread over insulated electrical wires. The intricate heat transfer process from flame in gas phase to the in depth of insulation and metal wire are elaborated to describe role of metal wire on the flame spread process. The work presents simulations in normal gravity and microgravity. The work has significance to fire safety as electrical wire short circuits are one of the key sources of fire in both terrestrial and space environments. The present study advances the understanding by using most realistic numerical model so far to bring insight on the heat and mass transfer process in flame, insulation and metal resulting in flame spread over insulated electrical wires. The model is an important step towards modelling real world fires on insulated wires.