A VO2 resistor, which switches from high to low resistance as it passes through a phase transition at 68 °C, can eliminate the initial current surge when an incandescent lamp is first turned on; this inrush current, which is often harmful, occurs because the cold resistance of the lamp is low. We here analyze the progress of (and the instabilities in) the electrically driven thermal switching of VO2, and determine the size and properties that a current-limiting resistor must have. Current limiters were made from a ceramic with a VO2 base and various additives; such limiters work well, and the steady-state power loss in them is 0.5% for 100-W lamps.