Insulation resistance confusion

[Calebp43]

Been to a fault finding job and lights where tripping the rcbo. After further investigation we found that it was a blue strapper cable (old wiring) from one switch to another using 3 core. Let's call this cable 1.
After hacking some of the cable out the wall we found that the other flat t and e had a partially broken live conductor. Let's call this cable 2.
So we fixed that but for some reason after we fixed cable 2 we then did an IR on cable 1 on all the 3 cores individually to the CPC in cable 1 and was getting 0.01, 0.02 and 0.03 ohms?!
it's worth noting that we disconnected cable 1 from the other switch and separated all the cores, so we where just testing that cable.
we put everything back together to see if it worked and it did. The rcbo didn't trip even with the loads.
the wall was like a 15 foot high wall that the cables where chased into and the customer was watching the whole time and didn't was us to keep chasing out if it wasn't necessary as it was working.
I left that job very unsatisfied and can't seem to grasp how the cables with such a low IR reading to earth isn't tripping the rcbo. Any thoughts? Thanks.

 

[Calebp43]

No, it's 0.0115 - you are an order of magnitude out!

0.115 would be 115mA and would definitely trip an an RCD.

It's vital you get your units and values correct. The two errors you have made mean your results are wildly out.

Literally mis-typed that's my bad. I wouldn't have got those units wrong when telling who I'm testing with the readings as it's right in front of me. Appreciate the feedback though.

 

[Calebp43]

Ok, well its good that you are coming to these forums to learn. Sometimes faults like these can be difficult to pin point.
As an apprentice I would suggest that its not your fault. But as Lucien described in his post faults like this need to be rectified, not just ignored just because the RCBO doesn't trip.

It's the responsibility of an electrician to ensure that an installation is left in a safe order. This may mean rectification of a fault or isolation of a circuit until the fault is rectified.

If the fault is there and the results are confirmed as per your readings, then I maybe would have isolated the circuit and explained to the customer the situation and the potential danger. If the customer then decides to ignore your advice/recommendation and then switches the circuit back on, then well, that's their call.

The bottom line is, based on your current position, the fact that you are an apprentice, then I would suggest that its the call of the senior electrician to make or if not then the main person responsible (your boss).

Thanks a lot for your thorough response. Greatly appreciated

 

[DPG]

Let's hope he has gone back to do further investigation, or maybe disconnect the suspect cable.