TNCS ze= 0.42

[robertarathoon]

Hi guys recently had supply authority out to replace their cable which ran through the house which i am working in because it was over 40yrs old, however carrying out inspections on the supply at the start i noticed that the ze measures 0.42 however the earthing arrangement is tncs (maximum allowed 0.35) so contacted the supply authority who came out, said they fixed it but there is no change at all any ideas what to do next?

 

[DonkeyDong]

Hi there,

There is nothing to actually state that the value has to be below 0.35 (so I believe).

That is the recommendation that the DNO's should be able to achieve.

Depending on the location, some values are over 0.35 (very long distances from the transformer) - although saying this, most locations should be below 0.35.

D.

 

[steptoe]

Hi there,There is nothing to actually state that the value has to be below 0.35 (so I believe).

That is the recommendation that the DNO's should be able to achieve.

Depending on the location, some values are over 0.35 (very long distances from the transformer) - although saying this, most locations should be below 0.35.

D.

totally agree,

this is only a value that BS7671 is based on,

herein beginith the lesson for the great unwashed,

do you now know how to ensure your work complies with the LAW now you can no longer compl,y with the novel that is BS7671...???

sort the sparks from the book readers now,!?!?!

 

[sirsparkabit]

totally agree,this is only a value that BS7671 is based on,

herein beginith the lesson for the great unwashed,

do you now know how to ensure your work complies with the LAW now you can no longer compl,y with the novel that is BS7671...???

sort the sparks from the book readers now,!?!?!

Expand please steps(for the unwashed) ]

 

[paulh]

The men in white coats say enquiry is the recommended route. if this is so then give them a call and when they say 0.35 you can say please fix my supply or advise how I can possibly comply?

 

[kme]

Not TECHNICALLY your problem. As long as you`ve made them aware that the figure is above THEIR recommended maximum, it has no further bearing on your installation; of which the pme connection is NOT a part.

 

[The Godfather]

If the Zs of the circuits within this installation exceeded the limits of BS7671 tables as a result of the 'raised' Ze, then my boys would be concerned.

However it is not uncommon from time to time to see a raised Ze (above what one expects), but as I have stated as long as all Zs measurements comply, then simply note on documentation, deviation from expected result (Ze).

Don

 

[steptoe]

its really an issue between the client and supply authority.

if you moan too much they may even withdraw your PME completely.

the simplest route is to either TT the system(much better anyway IMHO)

or simply ensure that you leave the installation safe and note the deviation in the box on the cert.

I have seen at various stages where the R1 R2 readings have been used and the 0.35 quoted on the cert and Zs done by calc, this is fine so long as you note this point on the form and also the fact that the actual readings do not comply with BS7671.

personally I would just verify that the protective device will disconnect within the specified time limit, thus complying with BS7671, that is the only reason that max Zs values are quoted in it, doesnt mean that if you get a higher reading that the device wont disconnect, just that according to IEC/BS if your reading falls below this then you have ensured your trip time is quick enough.

 

[DonkeyDong]

As stated, the actual value of Ze isn't too important......

As long as your Zs complies.

If your Zs does not comply, and the DNO can't get the Ze down (and you cant get your R1 or R2 down) then you will have to TT it (use RCD to comply).

D.

 

[kme]

Which you`ll likely be doing now, anyway!

 

[robertarathoon]

cheers guys for all your help will chech that zs results comply when carrying out tests on installation, and if so i will note the high ze reading in the box on certificate. Cheers for all your input rob

 

[extension15]

Rob, I've only ever encountered 2 installations similar to yours, just a shade over and not really worried about it too much..

But noted it down on relevant documentaion at the time..

; \