Temperature Correcting Cable Tests?

[big john]

Anyone have any information on temperature correcting insulation resistance values for low- and medium-voltage cabling?

I can find general references to keeping everything corrected to 15°C but very little in the way of tables for correction factors or anything else that might be used to actually make that adjustment.

Is this just not a widespread industry practice? Thanks.

 

[luckylerado]

Anyone have any information on temperature correcting insulation resistance values for low- and medium-voltage cabling?

I can find general references to keeping everything corrected to 15°C but very little in the way of tables for correction factors or anything else that might be used to actually make that adjustment.

Is this just not a widespread industry practice? Thanks.

What is the application? Megger / Hi-Pot?

I have never heard of applying a correction to the insulation resistance.

 

[big john]

What is the application? Megger / Hi-Pot?

Either.

...I have never heard of applying a correction to the insulation resistance.

I haven't seen it on any test results for cable. But it's a common correction when we do for rotating equipment, and I just wanted to make sure I wasn't dropping the ball on the cable test results.

 

[big john]

Bunpity bump. I know there are some testing guys on here, no other opinions?

 

[mivey]

You should correct if using an IR test but tests like the PI test are used to avoid temperature sensitivity. Whatever you do, just be consistent.

The manufacturer can give you the correction factor as they may differ, For example,
Southwire:
degF | XHHW/RHH/RHW/USE | THHN
50d | 0.73 | 0.56
55d | 0.86 | 0.75
60d | 1.00 | 1.00
65d | 1.17 | 1.34
70d | 1.36 | 1.79
75d | 1.59 | 2.40
80d | 1.86 | 3.21
85d | — | 4.30

Cerrowire:
degF | THHN
45d | 0.24
50d | 0.39
55d | 0.62
60d | 1.00
65d | 1.61
70d | 2.59
75d | 4.18
80d | 6.73
85d | 10.80

General Cable says:

The value of the insulation resistance at a temperature of 15.6°C (60°F), or when corrected to this temperature, shall not be less than the value of R calculated as follows:
R = K * LOG10( Dd )
Where:
R = insulation resistance (Megohms-kft)
K = insulation constant
D = diameter over insulation (in)
d = diameter under insulation (in)

Nexans has this:
R_standard = R_Measured / e^(T_Standard - T_Measured) / LN(insulation coefficient)