High Ze/s - BEWARE!

[securespark]

Went to trouble shoot at a customer's in Brum today.

The system was noted down by another engineer as TT, but with no rod.

I got there and did an EFL. Came back as middle 60's. Looked at cut out - containing 2 x PVC clad cables coming down the wall from outside. Possible TT, I thought. Went outside. Absolutely no trace of earth conductor or rod anywhere.

Couldn't be PME, surely? Traced a 10mm2 cable that went to cold water pipe feeding the shower.

Customer told me the reading the previous engineer had was 29 ohm.

Why had it suddenly jumped up to 65?

Ah, customer had water board in to renew 'cock, and they had fitted a new polypipe to the property.

Turns out the system was PME, but the DNO had failed to fit a link from the cutout to the busbar in the CU......

Unusually, the dno came out within the hour, and fitted the missing link.

I'm sure it's not the first time a DNO has cocked up bigtime, but......

 

[Adam_151]

Just wondering if testing EFL is the wisest thing to do if there is no visible earth path... (not having a go or anything, its just I understood it wasn't the thing to do because in the case of no earth at all the supply voltage will appear on everything connected to the earthing system)

anyway, its not *that* uncommon, recent example from over at the IEE forums: http://www.theiet.org/Forums/forum/messageview.cfm?catid=205&threadid=9528&highlight_key=y

 

[Lectrician]

When the DNO originally connected up, the spark should have done his testing once the supply was energised. This should never have been missed.

When instructing the DNO to connect, most DNO's have a completion certificate of their own they require you to fill in and sign. Nothing fancy, just want to know the loading, earthing type etc. If the spark didn't fill this in correctly......

PME may not have been available to the property at the time of connection, and the spark fitted the wrong type of board/protection.

Can't point the finger directly at the DNO

 

[securespark]

Can't point the finger directly at the DNO

Yes we can.

They fed a new cable to the house and connected it up as PME to the existing CU, , but just forgot the earth link to the cut-out.