The DC insulation resistance is a measure of the condition of the insulation. Determining its exact value is necessary to test various electrical circuits and electrical equipment.
The standards that should be checked during testing are determined by GOST, PUE and a number of similar directive materials.
Megohmmeter
The main purpose of this device is measuring insulation resistance of electrical equipment . It represents a voltage source and includes:
- DC generator (operated primarily by hand drive);
- magnetoelectric ratiometer;
- additional resistances.
Due to the presence of a constant current source, the megohmmeter allows using a voltage of a significant level for testing (at the same time for several devices or circuits). But it should be borne in mind that if the megohmmeter is connected to a device with a lower resistance level, then the megohm meter leads also show a reduced voltage level.
Insulation resistance test
Before analyzing the state of the device, you should make sure that the object is not energized, remove the dust and dirt from the insulation and ground it for two minutes (this allows you to remove the residual charge). During measurements, the megohmmeter needle must be stable, this is achieved by quickly and evenly rotating the generator handle.
The insulation resistance level is shown by the arrow of the measuring device. When the test is over, the DUT should be discharged. An important factor when measuring the resistance value is the temperature not less than + 5 ° С (without taking into account specially stipulated cases).
Grounding
It is possible and necessary to measure resistance not only for objects directly connected with electricity. In some cases, specialists have to measuring soil resistivity . The meaning of the procedure is to identify the effectiveness of grounding, which gives the soil (if the value of this parameter is not high enough, appropriate measures are taken). Ideally, resistance should tend to zero, but in reality this does not occur at all, but the situation can be regulated, this is why appropriate checks are needed.
