UEi Test Instruments DMEG3 - Manual (Page 8)

This chart interprets some possible data.
Extended Term Analysis
These methods incorporate comparisons of resistance values recorded
at different points of time (up to ten minutes). They can provide useful
information about the condition of your equipment even if PM records
are not available.
Generally speaking, the resistance measured at the end of 5 or
10 minutes should be higher than it was at one minute. The best way
to determine a good or bad reading for your specific application is
to solicit information from the manufacturer or evaluate new and
progressively older equipment.
60-30 Testing
The ratio of a reading recorded at 60 seconds compared to that
recorded at 30 seconds is one method that gives you a Dielectric
Absorption Ratio (DAR). This ratio provides you with the Polarization
Index (PI) when you divide the reading observed at the longer term by
that of the shorter. The rule of thumb regarding this index (60-second
reading divided by 30-second reading) is that it has to be higher than
“one” to be acceptable. Anything that has a ratio under 1.25 should
be watched carefully and anything over 1.4 is good. Because of the
time-frames specified, this test can be difficult to perform and is not
commonly used.
10-1 Testing
The methods of obtaining the ratios and index numbers are the same in
this test method as used in the 60-30 test, but the duration of testing is
extended. A measurement is recorded at 1 minute and another one
recorded at 10 minutes.
This Polarization Index table applies to both test methods:
To Make An Extended Term Analysis
1. Check and record equipment temperature.
2. Check dew point temperature of the ambient air-equipment
under test must be above dew point temperature for
accurate results.
3. Ensure no power is applied to the equipment under test and all
connections are removed in order to totally isolate the motor,
cables or equipment form other circuits. Use the connection
tables to determine where to make connections.
4. Turn your instrument power on (DMEG3).
5. Place rotary function select switch to the “INSULATION“
position, with the correct voltage selected - Use the same voltage
every time.
6. Make connections according to the sequence tables provided or
as your circumstances require.
7. Using a stopwatch or watch with a second hand, begin your test
at the same time you press and hold (or lock) the “Press to
Test” button.
8. At the end of one minute, read and record the insulation
resistance value.
9. Continue testing and record the value at the end of 10 minutes.
10. Evaluate results based on the Polarization Index table.
Following page: Copy and use the following PM data sheets to record
and monitor insulation resistance values of the equipment you test.
DMEG3/IRT3-MAN P. 7
Megohms
(Fig 5)
Insulation Condition 60-30 Test PI 10-1 Test PI
Bad Below 1.0 Below 1.0
Unreliable 1.0 to 1.25 1.0 to 2.0
OK 1.4 to 1.6 2.0 to 4.0
Excellent Above 1.6 Above 4.0