High Ze reading, what to do?

[TPES]

TN-CS at 0.54

What do you do? Is it down to the elec supplier, and not your problem to correct?

 

[GStueyXR]

DNOs problem mate... Really important for tn-cs too, so they will sort it sharpish!

 

[DurhamSparky]

Yup... defo There problem..! sounds daft and i know you will probably shout at me but when you ring DNO to inform them of fault get them to confirm what Earthing arrangements they have recorded for the Installation before you shed light

normally only applicable for half bodged conversions but always worth getting them to confirm your suspicion beofre you go and tell them what you found.!

 

[oldtimer]

Just had a similar problem with a CU change found that when I checked for Ze it was out of limits ie 0.94 on a TNS (parallel paths *&%$£) anyway they said that the house had never had an earth since day one . The cut out was 2 ceramic fuses at 60 amps on L & N so we will upgrade the cut out for you but £150 bucks for a earth connection where we will strip back the old cable back to the sheath and connect an earth on to it they said.

The house is an old 4 bedroom Victorian flat and due to parallel paths via the water and gas the guy down stairs
will get an improved earth ?? funny thing is the DNO came out to install an isolator switch and mentioned they could not change the fuse cut out as this was another department and at the same time I thought they would have done the basic tests such as Ze PFC PSSC etc but not a jot.

As for the existing earth clamp on the incoming cable they said nothing to do with us this must have been done by the previous sparky who put in the last board

 

[TPES]

My situation is another sparks certificate, I was in the house and the owner said I could look at the cert.... so I had a nose,

He's even ticked TN-S so it doesn't look odd if anyone see's the cert

 

[DurhamSparky]

lol.... nearly as good as a job i went to, customer provided cert and i had a check through.... TT was ticked and the readings suggested it to be TT.

However in the box with rod location he wrote "UNKNOWN" considering he changed the box i would think that this would be a must....

 

[dichroic]

Im confused reading this post ??

I accept that if you ring DNO they will quote a maximum of 0.35 Ohms for a TN-C-S earthing system.

However the chances are that this property is at the end of the supply cable furthest from the transformer which is giving a slightly higher than rated ZE reading.

ZS=ZE+(R1+R2) so unless this ZE is affecting the overall ZS value on the circuits concerned where is the problem?

If the overall ZS is 80% or less than tabulated values in BS7671 the protective device will disconnect in time.

Regards

Dichroic

 

[Des 56]

I am not absolutely sure on this statement,but my understanding is that the 0.35 figure given to us for a Tnc-s supply can,if the supplier wishes, be a maximum of 0.8 ish
They are not chained to that figure,the regulations they work to allows them a greater flexibility

As stated by dichroic,if the Ze+(R1+R2) is within max permitted,there should be no need to be overly concerned
A note on your certificate of the excess reading may not go amiss

Also variance in meter readings may account for the small amount exceeded

 

[GStueyXR]

With TN-C-S they have to guarantee Low Ze through PME, pretty dangerous otherwise. Nothing to do with disconnection times, just safety of consumers.

 

[Peter 55]

No ze reading or PFC

 

[DPG]

July 2010 this one

 

[ipf]

July 2010 this one

...and he's got a Ze reading, anyway, unless it's worn away after 10 years.