Insulation resistance test on a damaged conductor

[Lucien Nunes]

I have noticed that when doing the IR test, I have to hold down the Test button for several seconds before the meter reaches the maximum reading. It's not instant. Its that normal?

Yes. There are two main mechanisms at work here: Capacitance and dielectric absorption.

The voltage source in the tester has a maximum output current of a few mA and only 1mA at the full 500v, so it takes a finite time to charge the capacitance of the installation. On a small circuit that would be within the settling time of the meter indication but a large circuit and/or connected suppression capacitors can give a noticeable delay reaching a steady value.

Then there is dielectric absorption. Insulating materials unavoidably contain some molecular dipoles that store charge by re-orientation, but this charge storage cannot be charged or discharged rapidly. When subjected to a voltage change, a tiny current continues to flow for a while while the charge is 'absorbed' into the material which can cause an insulation reading to rise slowly over a minute or so. The same effect occurs when discharged.

 

[LastManOnline]

But what if there was a nail smashed into a conductor but not completely severed the conductor. Would that result in a pass on the continuity test?

Yes it would.Your insightful questions highlight the limitations of our current testing equipment.Electricians cannot locate a conductor that is damaged but not severed.It is entirely possible that such a situation could occur and result in a "hotspot" due to high resistance.On the other hand such situations are extremely rare.