A common voltage for an IR test is 500 volts, a thermocouple wire is not normally intended for running at high voltages respect to the chassis ground, thus its insulation is nothing special, I would set the test to twice the maximum working voltage specified by the thermocouple wire Mfr. or 500 volts if not known.

Regards

May be you are looking for something like these:

ASTM E780 - 06(2011) Standard Test Method for Measuring the ...

ASTM E839 - 11 Standard Test Methods for Sheathed ...

Ludicrous....some people believe all electrical cables must be treated equally. But wait, is this an Inspector insisting on the test? If so, don't mention 'ludicrous'...explain that all T/C voltage ranges are in millivolts only...

The issue may be simply be QC issue for the cable (lack of documentation/ traceability) rather than actual technical considerations...

Friends,

The only good reason I can think of, to justify an insulation resistance test, is to prove that the cable's insulation will resist any externally-applied voltage if a nearby cable's insulation were to fail. In other words, you don't want a fault to punch through the cable's insulation with a voltage that could fry the instrument. This degree of voltage protection is a code requirement in many low-voltage control and signaling systems' wiring.

--JMM

I do not understand LLP, but "Flare" suggests you have flammable gas present.

In that case, even circuits "intrinsically safe" against gas ignition risk have 500V insulation wherever practical.

This is because an electric "short" fault inside a flameproof motor [for example] returns current through the earth cable. Because live and earth conductors are about the same resistance, the case of the motor is at half supply voltage until the fuse blows - so is the sheath of any thermocouple bonded to the motor case.

To ensure safety, a spark between the earthed tray/conduit and thermocouple wires must be avoided by robust insulation. Because the thermocouple tail wires are vulnerable, the whole thermocouple assembly has to be 500V (DC) test rated.

Your first step should be to find out the test voltage at which the thermocouple and its cabling are rated. If less than 500V, the second should be to find out what voltage they ought to be specified at according to the contract spec. and any standards it lists.

If the contract did not require 500V test you can offer a test (at a rated level) - at extra cost!