Bridge crane and Gantry Crane
“Crane metal structure must have a reliable electrical connection; work in the track of the crane is generally grounded through the wheels and rails,” and provides “ground connection is not less than 150 square cross-section of flat steel or 10 square copper, Using Welding method connection. Under normal circumstances, the metal structure of the crane and all electrical equipment, metal casing, pipe trough, cable metal casing and driver’s cab are reliable connection with the cart wheel. Therefore, the emphasis should be placed on the test crane ,Running track and the grounding line connection. According to the “Rules” requirements, at the same time with the following four is considered qualified by the ground installation:
1) at any point on the crane grounding resistance is not greater than 4 ohms.
2) the grounding line cross-section not less than the “requirements”, that is, flat steel is not less than 150mm, copper wire is not less than 10mm.
3) ground wire and grounding body, ground wire and the car track must be reliable welding.
4) The joint of the two rail joint of the main rail is welded with a metal cross connection
However, there are two issues not detailed, in the test had been controversial:
A)In the neutral grounded power grid, should be grounded or connected to zero, many factories use a neutral point directly grounded three-phase four-wire power supply system. According to the principle of protective grounding and the relevant provisions of the work, in this distribution network of cranes, if the simple use of ground protection, and can not completely limit the leakage voltage within the safe range. On the other hand, the ground short-circuit current of one phase is not enough to cause the line protection device on the crane to operate when the single-phase leakage current of the crane power supply, and the dangerous voltage will exist for a long time. Therefore, when the crane power from the neutral point of the three-phase four-wire power system, can only take zero protection, and can not use the ground protection.
B) There should be at least a few ground connections in the same span, depending on the conditions of the units used. In the same span within the crane is also a little less, I think there should be at least two grounded, long track grounding point should be increased accordingly. Because after the long-term use of the rail track, due to poor fixation or lateral dislocation, it is easy to make the ground wire and track welding and rail joints between the jumper wire off, so there must be two or more ground wire is reliable.