Measuring the resistance of metal connections
Everyone knows that properly performed grounding is the key to the safe operation of electrical installations. But not everyone pays due attention to regularly checking the metal connection of this grounding throughout the entire life of the electrical installation. The whole check comes down to making sure that all grounding lines are in good contact. Indeed, due to the values of the contact resistances exceeding the standards the likelihood of a high potential on the installation body increases, and, as a consequence, it is increases the likelihood of personnel being injured by electric current.
How is the metal connection checked? The technique is pretty simple:
- Visual inspection, during which all welds are first tapped lightly to check their mechanical strength. Then the existing bolt or terminal contacts are checked for the quality of their tightening and the absence of any visible damage (chips, cracks, etc.);
- Testing the entire chain for compliance with its requirements of the electrical installation rules — is the measurement of the contact resistance of each of the available contacts. The chain investigated for metal connection includes the contact terminals of the main grounding bus, on which the PE conductor and the equipment grounding buses are closed, as well as the points of connection to the grounding conductor.
One more question is appeared: which device is optimal for measuring this contact resistance: a multimeter or a milliohmmeter? Here it is worth returning to the standards, which speaks of the normalized value of this contact resistance, which, for example in Russia should not exceed 0.05 Ohm (in explosive rooms and zones, the contact resistance should be no more than 0.03 Ohm). Hence, we conclude that for this case a specialized device is needed, because you can’t use simple multimeter, since the resistance of the wires with probes can reach 1 Ohm. To measure in proportion of an ohms, needs the device with a four-wire resistance measurement circuit, which excludes the influence of wire resistance on the measurement result. The choice is obvious: a micromilliohmmeter, which has the required accuracy and affordable price, will be an indispensable device for measuring the resistance of metal connections.
The company Chelenergopribor produces the IKS-1A micromilliohmmeter, which is necessary and sufficient for measuring the resistance of metal connections.
So, to measure the resistance of a metal connections you need:
- Connect the probes of the IKS-1A Micromilliohmmeter to the points located on both sides of the test connection, ensuring contact of all measuring probes.
- By short-term pressing of the «Start» button, start the measurement.
- After displaying the results on the device screen, enter the data into the protocol.
You can also need:
- Testing wires, 3 m long with spring-loaded probes — for measuring the resistance of metal connections of objects to which it is difficult to attach a “alligator” type clips, for example, cistern at a gas station;
- Testing wires, 3 m long with separated current “alligator” clamps and potential test probes — for circuits with multiple contact connections, each of which must be measured separately.