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Discuss Insulation resistance with broken line conductor in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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Hi, I'm not an electrician but I'm studying the material required for the C&G 2394/5 just for the sake of it. I think I understand the theory behind insulation resistance testing (but maybe not!) and the reason the test is performed at 500V (insulation condition, fault finding) and that loads need to be removed etc. Can someone explain what the reading would be in the image below and why? I think it would be greater than 999 Mega Ohms but that doesn't make sense to me with a break in the line conductor.

IR.jpg
 
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davesparks

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The reading would be whatever the maximum reading is for the meter, which typically is displayed as >999 on most meters these days.
A break in any conductor does not directly affect the insulation resistance reading, what it does is prevent full testing of the entire cable, the test will only show the resistance of the insulation up to the break.

Also that picture does not show a break in the line conductor, it shows a break in the conductor with blue insulation. Typically this would be used as the neutral conductor, but until it is connected it is just a blue insulated conductor.
 

Des 56

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If you are testing between A+B you are insulation testing as far as the break
After the break of conductor A,that section of cable will not be part of the test
Its as if you are testing a lighting circuit with the switch in the off position,to test the whole of the circuit switches are required to be closed
In your example the test lead needs to be moved to the other side of the break and a second test carried out
 
In the real world results depend on what actually caused the damage. Crushing ,stretching or damage+corrosion.
(Many test meter -Maximum values actually depend on test voltage )
 
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Thanks for all your responses, they all make sense. What I couldn't get was that in a lot of the fault finding videos I watch, they use IR as a tool to find the problem. Testing for continuity first would show this circuit had a break and an IR test would be of little use until the conductor was repaired/replaced?
 

ruston

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If as in your picture that was a lighting switch (appropriately sleeved) wire it would be an open switch. It is why we open and close switches; think multiple way switching, on our IR tests.
Continuity is an essential first test in testing as you have discovered.
 

davesparks

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Thanks for all your responses, they all make sense. What I couldn't get was that in a lot of the fault finding videos I watch, they use IR as a tool to find the problem. Testing for continuity first would show this circuit had a break and an IR test would be of little use until the conductor was repaired/replaced?
Yes an IR tester is the usual choice of tester for fault finding, but that is because traditionally an IR tester has both IR and continuity test functions in one box.
The actual tests you carry out will depend on what the fault is that you are looking for.

In your scenario if you arrive to a live installation with something not working the first test carried out would likely be for voltage at all points.
 

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