Measuring temp. on live conductors via batt powered thermometer and isolated DC PSU

[EK001]

Hi Everyone,

I went through thread248-419502 and I have a very similar situation where I need to measure the temperature at the point where the conductor enters a connector for UL requirements.

I am using a battery operated Fluke 54-2 digital input thermometer with a Type K exposed/bare wire thermocouple as this is how testing is done at UL as well. The thermocouple is attached (using Loctite 382) to the bare live conductor right at the point where it enters the connector.

AC and DC are both allowed for the testing however UL uses as low voltage high current AC source but I have a low voltage high current DC source and need to a test at 20A. The DC PSU is isolated as the negative is not tied to ground.

With an isolated DC PSU and a battery powered digital thermometer, are there any issues I can incur with the thermocouple being adhered to the live conductor directly? Do you foresee any issues with stray currents or potential damage to the digital thermometer? Since everything is isolated my guess is that I should be OK but I wanted to know if anyone else had experience with such testing before I go ahead and actually conduct a test.

Thank you.

 

[waross]

Are you able to momentarily interrupt the main current long enough to take a temperature measurement, to confirm that the measurement is valid with the main current flowing?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[EK001]

@waross, yes, I should be able to hit the output button on the DC PSU to kill the output momentarily. If temperatures jump around when I disable the output, I would know that something isn't right. Thanks for this tip.

More than the accuracy of the temperatures, do you foresee any potential damage to the digital thermometer with the bare TC being placed directly on a live conductor?

 

[EdStainless]

There will be a jump when you de-energise but it should then stabilize quickly.
What is the internal isolation in your meter? Some have limits on what potential they can tolerate on the incoming leads.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[waross]

There was a cheap and dirty trick that we used many years ago to measure the average temperature of pedestal bearings.
A hole that would just clear a thermo-couple wire was drilled in each side of the pedestal.
A thermo-couple wire was inserted into each hole and the metal peened beside each hole so as to firmly hold and contact the wire.
The temperature of the bearing could then be read by a suitable instrument. The indicated temperature would be the average of both sides of the bearing.
You may be able to experiment with something like this.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!