How is metal communication checked and what is it for?
Why take a measurement
Grounding is the basis of safety in electrical installations and in outlets. All electrical appliances and apparatus must be earthed. This is necessary in order to avoid electric shock in an emergency. Checking the metal connection is necessary in order to make sure that all grounding lines are in good contact.
The results of the verification are recorded in the metal communication measurement protocol.. You can see a sample of its filling in the photo below. After that, conclusions are drawn about the general condition of the grounding contacts and, if necessary, the problems are eliminated.
Maintaining metal communications in the norm allows you to:
- Avoid electric shock to both electrical workers and others.
- Eliminate hot contacts, reduce the risk of fire.
- Reduce energy leakage (contact heating).
What is the purpose of this procedure we examined, let's find out how it is carried out.
Verification Methodology
Contact with main ground bus happens bolted or by welding. Checking metal communications requires an accurate instrument - a milliometer, capable of measuring values of 0.01 Ohms and more accurate, but not vice versa. Measurement is carried out with a multimeter, if the latter corresponds to the accuracy and sensitivity class. Devices must be verified. You won’t be able to verify with a regular dial-up, it will show the presence of a contact, but its quality will remain unknown.
The verification and measurement of metal communication begins with an external inspection of the entire installation, the main attention is paid to:
- Gaps in the grounding busbars and wires. They can crack, tear, be destroyed by corrosion and so on.
- The quality of bolted connections. All bolts must be securely extended, and the busbars and cable lugs are stationary, i.e. should not move under any exertion.
- Quality of welded joints. They additionally tap with good, but not too strong hammer blows. This is done in order to detect cracks, the main thing is not to damage serviceable nodes.
How is verification done? Each metal structural element must be grounded:
- racks and metal frames;
- bearing elements;
- marching stairs;
- hoisting mechanisms;
- trays in which the wires are located;
- cable galleries;
- electrical panels;
- welding posts;
- door shields and more.
In order to measure the resistance, the first probe is placed on the main grounding bus, it is usually marked with green paint with yellow short stripes, and the second one is planned to be measured with a metal metal communication element. There must be a minimum number of connections from the end node or mechanism to the MSS.
The resistance of one transition contact should be 0.01 Ohm, its permissible excess is 20%. If there are several transitional contacts from the measured element to the main grounding bus, then their total resistance should be no more than 0.05 ohms. If the measurement results differ from the normalized ones, contact should be improved.
For bolted ones - either just a broach, or detachment, stripping of adjacent planes and a broach with bringing to normal in resistance, if the previous did not help. If the metal elements are connected not with tires, but with a flexible wire, you should also check the wire for kink, because the resulting metal bond resistance then increases. Welding joints must be restored. After these procedures, you need to check the resistance again.
The standards for measuring metal communications and their results are discussed in detail:
- PUE-7, section 1.7;
- PTEEE, p.p. 26, 28;
- GOST R 50571.16;
- GOST 12.2.0-75, paragraph 3.3.7;
Nuances
The metal bond measurement is carried out immediately after installation, right before start-up and start of operation, and then, with a frequency of 3 years, during scheduled tests and maintenance. Together with the check, as well as when changing the season, when flooding and excessive humidity are possible, check cable insulation resistance and electric cars.
Check the quality of the contact and measure it transition resistance Using a simple household multimeter, such as the DT830 and the like, will not work. In the field of small resistances, they either do not measure at all (up to tenths but not hundredths of an Ohm), and only the resistance between the probes in them reaches 1 Ohm, and sometimes even exceeds it. There is no need to talk about accuracy here.
Sometimes, to measure the quality of the contact, devices are not needed, since its destruction is obvious. In extreme cases, it comes to the point that you can measure its temperature by hand, if it is heated, it means that it needs prevention and subsequent measurements and verification with a milliometer.
Finally, we recommend that you watch the video, which clearly shows how to check for metal connections with the device:
Checking metal communications is very important for the life safety of employees and residents of the house. Due to poor grounding in outlets or its complete absence, there is a possibility of potential on the device body. And when a person touches him, an electric trauma or irreparable will occur. We hope the information provided was useful and interesting for you!
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