TN-S ZE 1.27 Ohms, previous cert shows 0.15

[robo83]

Just arrived at a job where a new consumer unit was installed by a previous electrician in 2010

Ive finished some garden lighting and started testing supply and I'm getting a reading of 2.7Ohms Ze and 1.08PFC this is a TN-S earthing system

Previous test sheet on the consumer unit was 0.15 Ze and 2.2Ka PFC

Ive informed the customer the earthing needs sorting by the DNO. I've refused to energizer my circuit unit it's sorted. Picture attached

 

[robo83]

Anyone noticed such a change in ZE in that period of time ?

 

[The Ghost]

How do you and the other electrician work out your pfc? I keep seeing figures for pfc on certs and this forum that puzzle me.

 

[Risteard]

How do you and the other electrician work out your pfc? I keep seeing figures for pfc on certs and this forum that puzzle me.

PFC is not the same as PEFC.

PFC is the greater value of PEFC and PSCC.

 

[telectrix]

EGGSACKLY.pfc should be the figure obtained L-N. except for PME systems, this will be a higher value than the PEFC.

 

[Midwest]

The clamp around the lead sheath doesn't appear to be the correct type?

 

[The Ghost]

PFC is not the same as PEFC.

PFC is the greater value of PEFC and PSCC

Great thanks for that. My question was how is it being worked out to the OP.

 

[telectrix]

and there'a a sticker missing..... "WARNING. THIS CU IS FILLED WITH PROTEUS CRAP. CARE SHOULD BE TAKEN WHEN RETURNING TO C.E.F."

 

[Strima]

Previous test may have been done with parallel paths in place.

I'm also going to stick my neck out here, does the circuit you installed have RCD protection? If yes then you could rely on the RCD to cover for the poor earth as a short term solution until the earthing problem is rectified. I know some will frown upon this but for me it would only be a temporary fix.

The DNO may well say convert to a TT and you could end up with an even worse Ze (Ra).

 

[robo83]

The circuit I installed was a 4mm SWA to CU in summer house. The consumer unit supplied a lighting circuit via 6amp mcb and RCD main switch

I discussed the temporary RCBO as a safety precaution for the supply SWA but explained ultimately it still isn't adaqute due to ZE.

My concern is the change in ZE from 2010. The homeowner said nothing has been changed since 2010 when they had the 2nd consumer unit installed. Which means the clamp for the earth was existing (this is a bonding clamp).

I did 2 tests, ZE was 2.70Ohms, I also did a loop test with all earths connected and I got 1.27Ohms. The 0.15Ohms and 2.2PFC from their install cert in 2010 must be either rubbish or there has been some change somewhere.

Ive issued a cert showing all my dead tests and sent them the DNO contact I use to arrange a check.

 

[polo1]

It’s perfectly possible that a cable joint has degraded, leading to a rise in the external loop impedance.
As has been said, one for the dno to sort out; might convert to pme or tell you to put in a rod.

 

[westward10]

I Ze can change in the blink of an eye, as Polo says this is likely to be an external breakdown issue. Fitting an rcd/rcbo is not a solution.

 

[Octopus]

I think the previous figure can be "assumed" to be correct ..... suppliers cables DO become faulty ............

The issue needs to be reported to the supplier and see what they say/do ............

Whether you can justify not energising the new circuit is debatable ........ I guess it will be how you dealt with describing the issue to the customer ....

 

[Deleted member 26818]

Refusing to energise a new circuit is easily justifiable.
Disconnecting an existing circuit or installation not so.

 

[buzzlightyear]

Previous test sheet on the consumer unit was 0.15 Ze and 2.2Ka PFC

I did 2 tests, ZE was 2.70Ohms, I also did a loop test with all earths connected and I got 1.27Ohms

hello at the back, which tester are you using
looking at those from 2010 look good to me .