gantry crane grounding protection
The problem of gantry crane grounding (zero) protection
1) no grounding device;
2) No metal jumper at rail joint;
3) There is only one grounding point in the span;
4) the ground wire cross-section is less than the standard;
5) the use of protective access to zero;
The following shortcomings to explain the above:
1) No grounding device It includes: the car track on the earth or the zero line without any metal connection, although the connection has been opened or the ground wire has been disconnected; there is connection, but the grounding failure. Some of the rails on the metal bearing rail beam bearing beam with metal pillars, so that the rail through the bearing beam and pillars constitute a qualified ground, in fact, this is not reliable. Because there is no reliable welding between the rail and the bearing beam, it is pressed on the bearing beam by the pressing plate, even the paper pad is padded, and the bearing beam and the pillar are painted with paint.
2) There is no metal jumper at the joint of the rail, and only the fishtail plate is connected at the rail joint. This is unreliable due to corrosion and so on. Some rail joints do not have plywood, Obviously not achieve the role of leakage protection, and then the situation is: ground wire fixed to the rail anchor bolts, and some ground wire welding in the end of the rail car stop on the iron block, and rail and rail are not welding, these phenomena are Is not conducive to security.
3) the ground wire cross-section is less than the standard, in general, the best use of flat steel flat. However, many units are used in round bar, “procedures” only that “ground connection is not less than 150mm cross-section of flat steel”, the bar section of the more appropriate not to be provided, may also press 150mm. The diameter of the round bar should not be less than 13.8mm, but most units with a 10mm round steel, individual units even with 4mm round steel, section is clearly too small.
4) there is only one grounding within a single span, which can be divided into two cases:
By the orbit to the earth only one ground; although there are two or more ground, but only one, the rest has no protection. Don’t work for many reasons, such as resistance grounding body value is too large, shall not go 4 ohms, some up to 20 ohm. The maximum to 62 ohm; some units with only one wire shallow buried in the soil as ground, easy to loose; some actual grounding wire broken or open welding.
5) with zero protection in low-voltage neutral grounding grid, should adopt zero connection protection. But in the inspection found that individual units part of the crane zero protection, another part of the crane grounding protection, which is not conducive to the safety of electrical equipment grounding system. Because it can’t ground.
The ground caused by unqualified for many reasons, but mainly because the ground understanding is not accurate enough, or ignore the welding renovation in orbit ground. Of course there is also due to the small scale enterprises, did not take the crane electrical safety in an important position. When the actual crane leakage occurs. Protective earthing or grounding is to ensure personal safety barrier of the event, should cause enough use of units.