Voltage on high res. extraneous part

[LastManOnline]

During an FLI test recently on a high resistance extraneous part (several thousand ohm) I decided to test what voltage appeared on the metal while the test was been carried out.I used a Metrel M1 3000.I measured approx 40 volt. Its well over 20 years since I conducted a similar test and my memory was of a higher voltage.? Is my memory flawed? Do others get similar type measurements with their testers?

 

[pc1966]

In think modern MFT / loop testers moderate the test current so they don't produce too big a change in supply (implying too high an exposed part voltage).

Certainly if you looked to design a loop tester with safety in mind you would put in some check / system so the test current was ramped up and limited by either 50V change or the "no trip" limit as the test started.

 

[timhoward]

Certainly if you looked to design a loop tester with safety in mind you would put in some check / system so the test current was ramped up and limited by either 50V change or the "no trip" limit as the test started.

In GN3 it states that for 2 wire high current tests, the instrument should cut off the test within 40ms if the voltage rise on the protective conductor exceeds 50v during the test. Are you sure you didn't write it?

 

[LastManOnline]

In think modern MFT / loop testers moderate the test current so they don't produce too big a change in supply (implying too high an exposed part voltage).

This was really what I, m wondering about. The FLI test was traditionally regarded as potentially dangerous. Hence the requirement to carry out earth continuity tests on all exposed/extraneous parts first. But if as you suggest (correctly I believe) that modern testers are designed to reduce the voltage on the exposed part than by definition the potential danger of the FLI test is reduced as well.