Testing.. Never goes right..

[TPES]

sid
you will find as you do more testing that the readings often vary a little from what you would expect its a case of learning what is an acceptable difference not every circ will be spot on by the book

Ok, I had done a test today on a ring main in a farm house.

I had readings between sockets from 0.28 to 0.36, this is obviously out of the allowed 0.05. Theres no spurs.

Would you say this is acceptable although its not "by the book" and happily record down your r1+r2 as 0.36 ?

 

[scotsparky]

Magic the 0.05 ohms figure is a rule of thumb i use before hunting its not in the book!!. As spread of figures is only 0.08 ohms of a difference then i would recon its ok. However its only going by figues you have given.
There are meny reasond for this spread of reading such worn contaacts if your usin a plug to take loops, Diffrences in connections if you are using probes.
As Jason,Mark has already said its experiance that will tell you these things and if you should go hunting. Thing to take into account are age,usage ect if its 6 year old building getting its first periodic i would say its fine no worries but if its a 50 year old building showing sighns of wear have a think. It could be corrosion in terminals have a GOOD hunt. On older buildings be carefull!!

 

[Mr Mark Sparks]

i agree with scotsparky dont waste time on such a small thing youll find your own level in time in the mean while feel free to ask

 

[TPES]

Cheers for your replys.. appreciate it..

Also i cant find max Ze for different earthing arangements in the red book.. anyone point me in the right direction?

 

[Spudnik]

TNCS - 0.35
TNS - 0.8
TT - 1667 although 200 is acceptable but it could be unstable and so should ideally be under 100.

Page 11 OSG

 

[TPES]

TNCS - 0.35
TNS - 0.8
TT - 1667 although 200 is acceptable but it could be unstable and so should ideally be under 100.

Page 11 OSG

Cheers J

I've measured Ze on a TT as 0.27

Would you say ive messed up somewhere on the test as this seems VERY low ???

 

[Mr Mark Sparks]

a neutral to earth ir fault will do this because the fault path will go down the neutral to get away quicker

 

[Spudnik]

Hmmm not convinced.

Did you disconnect the main bonds as per normal?

 

[scotsparky]

Magic please note that the Supply athority will tell you there earth on a tt system will not exceed 21ohms. Bit like tncs-0.35 an tn-s .8

 

[spark1]

Cheers J

I've measured Ze on a TT as 0.27

Would you say ive messed up somewhere on the test as this seems VERY low ???

If you positively isolated the Main Earthing conductor from the Earth bar and main bonds then you will probably be reading through a parrallel path close to your earth rod...maybe a water or gas pipe....if this is your reading then record it on your test sheet but note down your reason.