Metalworking Overhead Crane Hazard Factors - Ground Wire

Metalworking Overhead Crane Hazard Factors - Ground Wire

 

As the top in the industry, Dejun Crane is extremely cautious in the safe use of cranes. In this article, the ground wire will be described in detail. The main purpose is to remind everyone to pay attention to the safety of the crane when purchasing a crane.
 

(The electrical safety described in this article applies to all electric-driven cranes, including but not limited to: bridge cranes, gantry cranes, cantilever cranes, hoists, etc.;

it is also applicable to cranes of all tonnages: 10 ton, 20 ton, 50 ton, etc.)

 

1. The metal structure of metal processing cranes must have a reliable electrical connection; cranes working on rails can generally be grounded through wheels and rails.
 

2. It is advisable to use flat steel with a cross-section of not less than 150 square meters or copper wires with a cross-section of 10 square meters to connect the grounding wires, and connect them by welding.
 

Under normal circumstances, the metal structure of the crane and the metal casing of all electrical equipment, the pipe groove, the metal casing of the cable and the driver's cab are all reliably connected to the wheels of the cart.

 

Therefore, the focus of checking the grounding of the crane should be on the connection between the running track of the cart and the grounding wire.

 

 

According to the relevant requirements, only the following four conditions are met at the same time to be regarded as a qualified ground installation:
 

1. The grounding resistance at any point on the 100 ton bridge crane is not greater than 4 ohms.
 

2. The cross section of the grounding wire shall not be smaller than the requirements of the "Regulations", that is, the flat steel shall not be smaller than 150mm, and the copper wire shall not be smaller than 10mm.
 

3. The grounding wire and the grounding body, the grounding wire and the cart track must be reliably welded.
 

4. There is a metal jumper welded at the joint of the two rail joints of the cart track.

Problems Existing in Grounding (Connecting to Zero) Protection
 

1. No grounding device;
 

There is no grounding device, which includes: There is no metal connection between the cart track and the ground or the neutral line. Although there is a connection, the welding has been opened or the grounding wire has been disconnected; there is a connection, but the grounding body is unqualified.
 

There are also some who put the rail on the metal supporting beam, and the supporting beam has metal pillars, so they think that the steel rail has formed a qualified ground through the supporting beam and the supporting pillar, but this is actually unreliable.
 

Because there is no reliable welding between the rail and the rail support beam, the pressure plate is used to press the rail support beam, and there is even a paper pad in the middle, and the rail support beam and pillars are all painted.

 

2. There is no metal jumper at the rail joint;
 

There is no metal jumper at the rail joint, and the rail joint is only connected by fishplates. Due to corrosion and other reasons, this is unreliable. Some rail joints do not even have splints, and the rail gap width is 10mm. No leakage protection effect.
 

The situation that has again is exactly: grounding wire is fixed on the rail pressure plate bolt, and what have is welded on the iron stopper of cart track end, but iron stopper and rail are not welded, and these phenomena are all unfavorable for safety.
 

 

3. There is only one grounding point in the whole span;
 

The section of the grounding wire is smaller than the standard. Generally speaking, it is best to use flat steel for the grounding wire.
 

However, many units use round steel. The "Regulations" only state that "the flat steel with a cross-section of not less than 150mm should be used for the connection of the grounding wire."
 

That is, the diameter of the round steel should not be less than 13.8mm, but most units use 10mm round steel, and some units even use 4mm round steel, the section is obviously too small.
 

4. The cross section of the ground wire is smaller than the standard;
 

There are only two cases where there is only one grounding in a single span:
 

There is only one grounding wire from the cart running track to the ground; although there are more than two grounding wires, only one is effective, and the rest have no protective effect.
 

There are many reasons why it does not work. For example, the resistance value of the grounding body is too large. It is stipulated that it should not be more than 4 ohms, some can reach 20 ohms, and the maximum can reach 62 ohms; some units only use an aluminum wire to be buried shallowly in the soil. As a grounding wire, it is easy to loosen; some grounding wires are actually broken or welded.
 

5. Use protection to connect to zero;
 

Zero connection protection should be adopted in the low-voltage neutral point grounding power grid. However, during the inspection, it was found that some units connected some cranes to zero protection and another part of the cranes to ground protection, which is not conducive to safety. Because the electrical equipment of the zero connection system can no longer be grounded.
 

There are many reasons for the unqualified grounding, but the main reason is that the understanding of the grounding is not accurate enough, or the welding of the grounding wire is ignored after the track renovation.
 

Of course, some of them did not put the electrical safety of the crane in an important position due to the small scale of the enterprise.
 

In fact, when a crane leaks electricity, protective grounding or zero connection is a major event to ensure personal safety. It should be paid enough attention by the user. A regular inspection system should be established in accordance with relevant national standards and regulations, and management should be strengthened to prevent cranes from leaking electricity. resulting in personal injury.