Study on grounding safety(安全接地学习).docxVIP

Study on grounding safety Grounding safety is related with security of equipment and bodies. According to national norm, the kinds of grounding consist of protected grounding, work grounding, grounding of intrinsically safe system, static protective grounding, lightning protection grounding. 1 Grounding classification1.1 Protective groundingProtective grounding is a kind of grounding mode for security of equipment and bodies, exposed conductive part of instrumentation and control system which uncharged on normal status, fault, damage or abnormal situations may bring dangerous voltage, such devices shall implement protective grounding, the voltage of field instruments less than 36V which is not do the protective grounding, but except the equipment maybe contact with the voltage higher than 36V. When the instrument mounted on the metal dashboards, boxes, cabinets and frame, which keep good connect with the metal dashboards, boxes, cabinets and frame, protective grounding never need.1.2 work groundingWork grounding of instrument and control system consist of instrument signal circuit grounding and shielded grounding, isolated signal may not be grounding, the “isolated” means each input signal(or out signal) electric circuit keep electric insulation with other input signal(or out signal) electric circuit and the earth, the power independent. Generally non-isolated signal use DC power negative as reference point, and keep grounding. Principle of instrument work grounding is single point grounding, signal circuit should be avoid bringing out grounding circuit, if signal resource and receiving instrument all grounded in a line, the two grounding point should be isolated by using isolator.1.3 Grounding of intrinsically safe systemKinds of grounding of intrinsically safe system consist of isolated safety barrier and zener safety barrier. Grounding of intrinsically safe system with isolated safety barrier don’t need grounding. But grounding of intrinsically safe system with