How to avoid accidental electrification of electrical equipment of launching girder?
Usually there are two methods to avoid accidental electrician of electrical equipment of launching girder: protective connecting neutral and protective grounding.
Launching girder
1. Protective connecting neutral
Protective connecting neutral refers uncharged metal case or framework of electrical equipment in the normal condition, connected directly with guide line and power neutral line.
Main function:? as electrical equipment uses protection connecting neutral, once short-circuit trouble or destruction of electric insulation occurs, electrical equipment shell is charged. Because resistance of neutral line is very small, and short-circuit current is several times or even dozens of times higher than rated current, which will force protective motions in the electrical equipment or make fuse protector fuse within a short time, thus cut off power supply of failure equipment and protect safety of equipment and personnel.
2. Protective grounding
Protective grounding refers that uncharged metal case or framework of electrical equipment in the normal condition, connected reliably with ground by grounding device.
Protective grounding is suitable for low voltage power network with power supply neutral un-grounding of launching girder.
Main function: when electrical equipment insulation is destructed, the metal case will be charged. For grounding resistance of grounding device is very small, voltage to earth of metal case thus is greatly reduced. When human body touches with electric leakage shell, the shell and ground, people and ground are two parallel branches. When grounding resistance of electrical equipment become smaller, the current passing the human body is smaller, thus reduce electric shock harm to human body.
