Insulation Resistance

[sparkzalot]

So i have db1 in 1 block of flats for communial lights etc, feeding db2 via a swa feed underground. Ir at db1 to test every circuit and submains 0.01Mohms. (N+L together to earth)
Switch db2 off. All clear. Db2 also all clear when testing ir when investigating further.
Any suggestions??

 

[Dave OCD]

An item of equipment must still be connected [Fed from DB2] giving the low resistance between L & N ?

 

[Hellmooth]

An item of equipment must still be connected [Fed from DB2] giving the low resistance between L & N ?

He has L & N together? And DB2 is clear when testing on its own?

 

[sparkzalot]

No because db2 was all clear when testing that separately

 

[Richard Burns]

DB2 neutral must be fed from the supply directly rather than from the DB1 Neutral bar. Perhaps.

 

[sparkzalot]

No 1 of the cores was definitely connected to the neutral bus bar

 

[Andy78]

What further IR testing did you carry out after these results ?

 

[R G]

Isolate every circuit completely at both boards and make sure all equipment is unplugged or fully isolated and test each section in turn , simple ....

 

[sparkzalot]

No 1 of the cores was definitely connected to the neutral bus bar

 

[sparkzalot]

What i did. All clear. Was down testing the whole installation. Im thinking possibly the 2 rcds. Its pickled me any how...

 

[Richard Burns]

From what you describe, everything correctly wired and DB1 and DB2 with DB2 on are 0.01MΩ and with DB2 off is >200MΩ and all of DB2 is >200MΩ there can only be fault within the main switch of DB 2 to earth!

Since this is not possible unless there is a huge metal spike through the switch there is something missing. Did you test DB1 and DB2 together after testing DB2 as clear as it may have then been OK.
Perhaps someone realised you were testing and removed the offending item.
(I have had this; testing a circuit found the fault left one faulty cable, one OK cable sticking out went to get a new cable, test again and both cables are now at fault, the customer had been "helping" by plugging everything back in, as I was nearly finished!)

 

[sparkzalot]

From what you describe, everything correctly wired and DB1 and DB2 with DB2 on are 0.01MΩ and with DB2 off is >200MΩ and all of DB2 is >200MΩ there can only be fault within the main switch of DB 2 to earth!

Since this is not possible unless there is a huge metal spike through the switch there is something missing. Did you test DB1 and DB2 together after testing DB2 as clear as it may have then been OK.
Perhaps someone realised you were testing and removed the offending item.
(I have had this; testing a circuit found the fault left one faulty cable, one OK cable sticking out went to get a new cable, test again and both cables are now at fault, the customer had been "helping" by plugging everything back in, as I was nearly finished!)

Im certain nobody touched anything being as it was the communial installation. Very strange though. But a ir test at db2 to prove no faults didnt really require another test back ad db1 being as all was clear.