Temperature Correction
Temperature has a very large impact on your insulation
resistance values. When using your meter for predictive
or preventive maintenance tasks, the readings must be
“temperature corrected” to 20˚C (68˚F).
The rule of thumb is, insulation resistance changes by a
factor of 2 for every 10 degrees of change in Celsius-scaled
temperature. That means that a cable that measures 150
Megohms at 20 degrees Celsius (or 68 degrees Fahrenheit)
will likely measure 75 Megohms at 30 degrees Celsius ( or
86 degrees Fahrenheit). Accordingly you would record 150
Megohms on your PM record (75 Meg x 2). Use the following
chart to adjust for this correction factor (Fig 3).
Temp
in C
10
12
14
16
18
20
22
24
26
28
30
32
34
Temp
in F
50
54
57
61
64
68
72
75
79
82
86
90
93
Multiply
Reading by
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.4
1.6
1.8
2.0
2.4
2.8
Temp
in C
36
38
40
42
44
46
48
50
52
54
56
58
60
Temp
in F
97
100
104
108
111
118
118
122
126
129
133
136
140
Multiply
Reading by
3.2
3.6
4.0
4.4
4.8
5.2
5.6
6.0
6.4
6.8
7.2
7.6
8.0
16
