One of the testguy questions was this,
When performing medium-voltage cable sheath testing, the test voltage is connected in such a way that the ____ potential is connected to the shield, and the _____ will be connected to earth.
a. negative, positive
b. positive, negative
c. any of these
It said the correct answer was “negative, positive”. Is this correct? Everything I found online said it should be “positive, negative”. I even asked ChatGPT, and it said to connect the positive wire to the shield.
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While the standard convention today is to connect + to the object you want “energized” and - to ground, in most instruction manuals for insulation resistance testers, it will indicate to put the + to ground and - to the specimen under test. This polarity goes back to old insulation systems that are hydrophobic (absorb moisture) and the way the water molecule migrates based on the applied electric field. In most cases, either polarity will get you similar results. However, if moisture is involved, you may get differing readings. Give it a try and see. Also, remember that when the insulation resistance test set is energized, it applies a difference of potential between the two leads. There are many that think that - is at 0 potential and the + is at the energized potential. Not so. I teach this to our new testers and it blows their minds!
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