continuity test on a protective bonding conductor

Yp510n said:

Hope i find someone who can help me with this one. I have this question on an exam:
A continuity test on a protective bonding conductor gives a result of 15ohms. What possible reasons for the result and what actions (if any) that should be taken?

My answers where:
-wrong size conductor shows high resistance cable so i must replace it by the correct one and do a retest
-conductor is damaged so cable must be replaced and restet
-connection of the clamp to the pipework has oxidised so it must be clean, reconnected and retested
-termination of the clamp if is not screwed correctly, it will need to be tighten properly and retest

After giving these asnwers my teacher told me many times that is wrong and i need to think as if i was an engineer (which I'm not) and need to write it as if I'm writting a report.

Aren't these the way an electrician write a report and most importantly... are these the right procedures?

Many thanks in advance

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I have suggestions for you to consider. Obviously I do not know what your teacher wants as an answer but perhaps you should be informing the duty holder (person responsible for the safety of the installation on a day to day basis) of the finding and consequences for the installation (safe or unsafe for continued use).
Perhaps the reading of 15 ohms can be summarised as due to either:
- damage, deterioration or corrosion and needs further investigation
or
- inaccuracy/error in the test instrument (which I think you would have checked and probably eliminated as possible cause before writing the report).

Assuming the reading is correct (e.g. you checked / zeroed the probes first) then realistically it has to be a poor connection or terrible levels of cable corrosion. You would need an enormous length of cable and/or very very thin (perhaps most metal corroded away) to get 15 ohms.

However you look at the value, it is very bad. Not your 0.1 ohm might be a bit long bad, but something that is next to useless for OCPD-based disconnection.

I think maybe your teacher is looking for what would be written on the report and what immediate actions might be required.

There is a clue in the type of conductor it is and its main function. So if you have such a high reading without further investigation you cannot determine the cause. However, prior to further investigation there maybe an action you need to carry out. And this Should be also noted on the report and coded accordingly.

Remember! The main purpose of inspection and testing is to determine the safety and suitability of an in service installation.

I think as others have said you might be over thinking the question, they may just want "Protective bonding conductor high resistance, bonding needs to be repaired or replaced"

If I was doing an EICR I would have to think someone is not paying me to find the problem, it could take hours to work out exactly what the issue is, it could be everything you have said, it could be parallel paths (Something like supplementary bonding), it could be the testing method, for example if might be the bonding conductor is broken and lets say its the water pipe, that pipe might be close to the gas pipe where it enters the ground, if the gas pipe is correctly bonded if you just test from the bonding conductor to the pipework of the water like you are supposed to then the high reading could be from the other pipe (I had this on my AM2)...

But the question does not give you any specifics or any other details so I think they just want you to report that the extraneous conductive part is not correctly bonded as the bonding connection reading is too high at 15ohms and should be 0.05ohms, the bonding conductor needs to be repaired or replaced..

15 ohms. Kind of about what I'd expect from a parallel path through the ground itself. Perhaps accidentally testing between ends of different conductors, eg bonding one end, earthing conductor the other? Either that or loose/corroded connection.

catdog1121 said:

But the question does not give you any specifics or any other details so I think they just want you to report that the extraneous conductive part is not correctly bonded as the bonding connection reading is too high at 15ohms and should be 0.05ohms, the bonding conductor needs to be repaired or replaced.

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I think this is the pertinent bit - not doing the fault-finding but noting and describing the fault clearly.

Somewhere i think I read the 0.05 ohm is really for the connections, if you have a long bond wire you ought to allow for the expected cable resistance, but in reality with 10mm and most home layouts you should be fine at <= 0.05 test.

should be 0.05ohms. wrong..... the 0.05 ohms reading sis the max. between the end of the bonding cable and the pipe to which it is bonded. nothing to do with the resistance of the cable.