“A Stitch in Time...”

Setting up a Maintenance program
To start insulation testing there is one general rule: Put first things first.
That is, review all the electrical equipment and classify it as to relative
importance. For example, if that AC motor failed in department A, how
would it affect overall plant production? Your production people can
certainly help in this and should be vitally interested in the idea.
If time permits at the start, test every piece of electrical equipment and
make out a record card. Possibly at first you will have to combine several
units but it will pay in the long run to have test records for each individual
unit. Then, if insulation weaknesses do show up, your job of tracking down
the offending part will be easier.
Shown in Fig. 40 is one form of test record card, which is available from
Megger. Following is the type of information, which becomes more valuable
to you as tests are repeated at intervals:
1. name and location of the equipment
2. Dates and values of test results (record actual reading at the time
of test)
3. Range, voltage, and serial number of the Megger instrument used
4. Temperature of the apparatus (also, particularly for large units,
wet and dry bulb temperatures – for humidity and dew-point
determinations)
5. Insulation resistance measurement corrected for temperature
6. A plot of consecutive readings to show trend and enable you to
anticipate failures
Figure 40
60
A STITCH IN TIME