- Aug 30, 2004 -
How to prevent accidental live accident from electric equipment of bridge crane
Nowadays, bridge cranes are all powered by electric power. In the installation and maintenance of overhead cranes, they are also inseparable from the use of electricity, grasping the safety knowledge of electricity and preventing electric injury accidents.
Protection of grounding and protection of zero are safe and technical measures to prevent the accidental electrification of electronic equipment and cause electric shock.
1. Protection of grounding
The protection of grounding is to connect the uncharged metal shell or frame under the normal condition of the electrical equipment, and use the grounding device to make a reliable electrical connection with the earth.
Protective grounding is suitable for low voltage power grid with ungrounded neutral point of power supply. It is the role of the insulation damage of the electrical equipment and the metal shell is charged, the grounding resistance is very small, the metal shell to ground voltage is thus greatly reduced, when the body and shell leakage contact, then the shell and the earth, and the earth was formed between the two parallel branches, and electrical equipment the grounding resistance is smaller, the current through the human body is small, so as to reduce the electric shock to human body in Shanghai.
2. Protection to zero
The protection to zero is the metal shell or frame which is not charged under the normal condition of the electrical equipment, and the wire is connected directly with the neutral line of the power supply.
The protection to zero is suitable for the three-phase four wire or three-phase five wire system of low voltage grounding grid, which is directly grounded in the neutral point of the power supply. It is when the electrical equipment with zero protection, once the equipment fault or electrical insulation damage, electrical equipment shell charged, the resistance of the neutral line is very small, the short-circuit current is greater than the rated current several times or even dozens of times, forcing the electric action in the protective circuit or the fuse in a short time, the power supply in order to removal of faulty equipment, protective equipment and personal safety.