An electrical bushing is an insulated device that permits electrical power to travel in and out of enclosures like transformers and circuit breakers. Electrical bushings are designed to ensure the electrical strength of the insulated material is strong enough to withstand the electricity passing through the conductor. Bushings must also be capable of withstanding moments of higher than average voltage.
Since electrical output is the product of voltage and current, bushing insulation must be able to withstand the voltage applied to it, and its current-carrying conductor must also be strong enough to carry related current without risk of overheating and damaging adjacent insulation. Bushings must also be strong enough to withstand various mechanical stresses. Bushings commonly utilize a copper or aluminum conductor wrapped in insulation, except for the exposed terminal ends.
A fixing device is typically attached to the insulation to secure it in position, and the insulation between this fixing point and the conductor is the area subjected to the highest levels of stress. Electrical bushing may utilize paper, resin or porcelain insulation depending on their intended uses. Bushings sometimes fail because of an event known as a partial discharge that may result from the slow and progressive degradation of the insulation over time.