Discuss Testing Questions - help. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

C

chrisgc

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

Following the On site guide for IR test and still getting used to testing was wondering why the following:

Readings:

L-N = 566.9 Mohms (Pass)
L-E = 475.9 Mohms (Pass)
N-E = 0.060 Mohms (FAIL)


Yet when I disconnect the earth from the earth bar I get this reading:

N-E = 352.2 Mohm (pass)

1) Why is it that doing it the way which is in the OSG (ie. earth still connected to bar) gets the fail reading on bold above?

2) Is it best to do it as per the OSG or to completely disconnect both Line, Neautral and Earth completely from CU?

3) Also When testing cooker circuit (and it indicates in OSG to test at 'each point') do I test at the back of the cooker control unit OR at the very end of the disconnected cable (the very end of cable which terminates into the rear of cooker?
 

keniff

-
Reaction score
105
Testing with the cpc connected to the met will them throw up any ir faults between pipe work also.....
 
C

chrisgc

Any advice as to what could possibly cause that reading - as still trying to learn and best way is to get problems like this as can learn from them?

Also any answers on the other questions in my original post?
 
D

Deleted member 9648

It is a requirement to IR test with the cpc connected to the means of earthing since the 17th edition.....the reason being that if there is a fault to an earth potential independant of the electrical earthing system on that circuit it may not show up with the cpc disconnected. You clearly need to investigate your N-E result.

@ no 3.....I assume you mean continuity testing?......if the cooker is hard wired test at the cooker terminations,the furthest point on the circuit.
 
Last edited by a moderator:

Strima

-
Esteemed
Reaction score
5,760
Following the On site guide for IR test and still getting used to testing was wondering why the following:

Readings:

L-N = 566.9 Mohms (Pass)
L-E = 475.9 Mohms (Pass)
N-E = 0.060 Mohms (FAIL)


Yet when I disconnect the earth from the earth bar I get this reading:

N-E = 352.2 Mohm (pass)

1) Why is it that doing it the way which is in the OSG (ie. earth still connected to bar) gets the fail reading on bold above? Most obvious answer quoted from Telectrix below.

2) Is it best to do it as per the OSG or to completely disconnect both Line, Neautral and Earth completely from CU? If you get good readings using the first method then all is good, any bad readings you then need to split down the circuits. First method saves a lot of time.

3) Also When testing cooker circuit (and it indicates in OSG to test at 'each point') do I test at the back of the cooker control unit OR at the very end of the disconnected cable (the very end of cable which terminates into the rear of cooker? Full length of circuit that is part of the installation.

The OSG is just a guide, a very helpful one, but if every method was put into it you'd need a bigger van. Testing boils down to common sense and interpreting the results you get, if you have a good understanding of how a circuit works and how it is installed with others it makes things a lot easier.

could it possibly be PME?
 

ackbarthestar

-
Mentor
Arms
Reaction score
604
could it possibly be PME?

I'm not sure that 60k ohms represents a N-E link.

However I would say that if the IR values are below 2.0M ohms (1.0M ohms) then further investigation would be required. Which from your results, is precisely what has been done.

Most electronic filtering in certain electronic appliances will produce these types of values.
 
D

Deleted member 9648

Strima......it is now a requirement to IR test with the cpc connected to earth,testing with the cable completely disconnected is not acceptable.....612.3.1
 

Strima

-
Esteemed
Reaction score
5,760
Strima......it is now a requirement to IR test with the cpc connected to earth,testing with the cable completely disconnected is not acceptable.....612.3.1
I should really get my head into the BGB, cheers for the heads up. This wasn't even mentioned on my 2391 when it should have been.
 
C

chrisgc

With regard to the fail on the N-E result on my IR test - whats the best way to breakdown the circuits to try and pin point the circuit causing the low reading?

Would it be to disconnect each neutral OR earth in turn then to do IR test? Then when I get to the circuit with the fault my tester will then be passing the N-E reading?
 

Reply to Testing Questions - help. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Top