A comprehensive 64 page guide to electrical insulation testing containing helpful diagrams, value tables, product information and much more!. over a period of time, and the location and importance of the equipment megohmmeter is connected to the insulation to be tested and is operated for a short. The Dielectric Absorption (or Time-Resistance) test is an extension of the Megger, “A stitch in time – The Complete Guide to Electrical Insulation Testing”, a free.

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See Safety Precautions, page Make Sure Just Tije is Included in the Test Inspect the installation very carefully to determine mfgger what equipment is connected and will be included in the test, especially if it is difficult stitfh expensive to disconnect associated apparatus and circuits. With good insulation, the conduction or leakage current should build up to a steady value that is constant for the applied voltage, as shown in Fig.

It is designed for other uses, too, but for insulation testing it provides: These tests are in addition to acceptance tests specified. Using a Digital Multimeter 4.

If you want to make reliable comparisons between readings, you should correct the readings to a base temperature, such as 20 C, or take all your readings at approximately the same temperature usually not difficult to do. In this chapter you will learn. Use rubber gloves when connecting the test leads to the apparatus and while operating the Megger instrument.

So, a suitable way of measuring resistance can tell you how good the insulation is. Any increase of leakage current with time is a warning of trouble, as discussed in the tests described in the following section.


Also make a test of all the components connected together.

Megger ‘A Stitch in Time’ Information Booklet on Insulation Testing

Any convenient length of lead may be used. Their presence could unpredictably affect your readings; they should be removed before tests are made. We will cover some general guides to temperature correction.

If the equipment is wet from fresh water, you go right ahead drying it out.

Affordable, sturdy, reliable Portable, battery-powered More information. Make tests at frequent intervals until the cause of low values is located and remedied; or until the meger have become steady at a lower level but safe for operation; or until values become so low that it is unsafe to keep the equipment in operation.

It will also test 6 or As a part of your maintenance records, therefore, it s a good idea to make note at least of whether the surrounding air was dry or humid when the test was made. For good insulation, the resistance usually reads in the megohm range. The initial surge of charging current, the drop with time to absorption current, and then, after more time, the steady conduction current.

Operating Time A very important consideration in making insulation resistance tests is the time required for the reading of insulation resistance to reach a maximum.

This may include series or parallel leakage paths through insulation or over its surface. In this chapter you will learn More information.

Megger ‘A Stitch in Time’ Information Booklet on Insulation Testing

If your equipment operates regularly above the dew-point temperature the temperature at which the moisture vapor in air condenses as a liquidthe test reading normally will not be affected much by the humidity.

The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. The clip on the Line lead is connected to the apparatus under test in the regular way.


Condition is probably all right, but cause of low values should be checked. Usually, however, it drops gradually, giving plenty of warning, if checked periodically.

Equipment Rating AC Testing vs. In this Investigation you will build circuits More information.

Support the lead only by its connections to the instrument and the apparatus. Read this operation manual and understand the description More information. Factors have been developed, however, to simplify the correction of resistance values. If neutral or other ground connections have to be disconnected, make sure they are not carrying current at the time, and that when disconnected no other equipment will lack necessary protection.

Before making these observations, be sure that all capacitance is discharged by short circuiting or grounding the apparatus. On the other hand, if past records showed the normal resistance values to run 10 or 20 megohms, then you would know that water was still in the motor windings. Tests by this method are sometimes referred to as absorption tests. Bhatia Continuing Education and Development, Inc.

Every electric wire in your plant whether it s in a motor, generator, cable, switch, transformer, etc. Current testing with the high-range 50, megohms Megger insulation testers requires that the Line test lead be maintained at a high value so that it will not enter into the measurement.

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