One of the most important parameters that characterize every element of the circuit - is its electrical resistance.Physical its meaning is in the properties of the conductor to provide resistance to the passage of an electric current.It depends on the structural features of the atomic structure of the material and external conditions.The numerical value of the electrical resistance of any circuit section can be easily calculated from the measured voltage across the gap, and force the current flowing through it.To identify a resistance sufficient to divide the voltage by the current.This is the famous formula for Ohm (its generic application).
addition to the direct payments, in practical work with electricity is increasingly used direct measurement of resistance.For this are special devices.One of the most well-known, allows even a person unfamiliar with electrical engineering to perform resistance measurement, is presented with a multimeter (digital or analog).Probes the device creates a certain voltage and current, knowing that it is easy to determine the resistance and display its value in the form of numbers on the display or deviation indicating arrows.
resistance measurement is not theoretical, but practical.Work related to maintenance of electrical circuits, requires frequent use of measuring instruments.Performing periodic measurement of resistance of their components, can ensure the continued operation of the entire installation.
Every person who is brought to face the maintenance of electrical installations, is very familiar with methods that perform insulation resistance measurement cable.Among them, the most simple and accessible is to use a special measuring device - ohmmeter.It is more correct to call it "Megger" (megger), since the insulation resistance of the cable, after all, is measured in thousands of ohms.
insulation test should be performed in any doubt about the change in its status.If there is a local damage (mechanical, thermal, chemical), the direct examination is not enough.Check the insulation is necessary in the event that water between the insulating layers of the cable, as well as the duration of its non-use.To set the stopwatch need megatester limits which allow you to measure the insulation resistance, and access to the stripped ends of the cable.Normal insulation resistance depends on the voltage at which the element is operated.For example, if the cable is used to transfer thousands of volts, it can be considered normal (minimum allowable value), if the condition 1 megohms at 1 kV.Lower voltage changes accordingly: 1 kilohms to 1 volt.
Most megohm meters as the source of the check voltage using a dynamo, so measurement is required to rotate the knob to the desired speed.Check the insulation of the cable are beginning to spread lived on both sides of the site, if it is possible (in the case of connecting them to one of the parties is verified total resistance that is acceptable, although less accurate).One probe Megger alternately applied to each core conductor, and the second - to the ground (earth).
When rotating the handle of the device is displayed insulation resistance is measured with respect to the core and the ground.If it is within acceptable limits, then spend the next dimension: is checked by the resistance between the conductors.For this purpose a probe is touched to an arbitrary conductor, and the second - alternately to all the following.Rotate, check the resistance value.When checking the Megger at a high voltage cable, so you can not touch him.After measuring each core should be discharged by touching it to a grounded metal object.
