The errors of a 2-stage current transformer (CT) are analysed when used as an isolated device or when used in a differential circuit. It is shown that when the CT is used in a differential circuit, or is operated at near zero external burden, a reduction in the errors of around two orders of magnitude can be gained. It is also shown that where the errors of a CT are largely a result of dielectric leakage, or of partial magnetic coupling, 2-staging will do little or nothing to reduce the errors.