Bolts, nuts electromechanical coupling is a basic industry of the assembly, when tight coupling bolts in the long-term effects of mechanical force and the electromagnetic force prone to metal fatigue, shear, such as silk or thread connection is too loose slip case assembling loose, so that between the components, causing an accident.For bolts, nuts joins current conduction of electrical engineering, not only to pay attention to its mechanical effects, but should pay attention to their heating effect, crimp is not tight, the contact resistance increases, generating heat when energized - contact surface oxidation - a vicious cycle of increasing resistance until serious overheating, seizure connection place, causing a short circuit to ground, disconnect the accident. For the primary equipment and bus lines and groove clamp connection, T-clamp, clamp device, wiring equivalent may therefore produce different degrees of accidents.