Ze Tns system

Hi guys

Been to finish a job off today, now on the initial inspection Ze on the Tns system was up and down but nothing major, now after powering it all back up I'd thought I'll re check the Ze.

Checked it 4x last time and 4th final time I placed my clamp onto a cleaned lead sheath right below where the earth is bonded on, got the same reading 

1.78 ohms on a Tns 

Time to call the boys out or what as ive read that other stories about DNO''s have come out and said it's fine, anyhow couldn't bloody get anyone at 12 oclock today saturday, typical

I'm not sure if it's max permitted, or recommended,  but 0.8 ohms rings a bell, 

steptoe said:

I'm not sure if it's max permitted, or recommended,  but 0.8 ohms rings a bell, 

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You are correct it is 0.8 on a Tns and 0.35 on an Tncs

This is a Tns supply and were at 1.78

I do have to go back to fit another mcb so I will recommend check with another meter, but I'm sure it's still gonna be 1.78 ohms 

But, is that a max permitted figure,?

or just recommended,?  Like the 200 for TT is only recommended,  but a lot of people think it's maximum permitted.

the OSG does funny things to a lot of people.

steptoe said:

But, is that a max permitted figure,?

or just recommended,?  Like the 200 for TT is only recommended,  but a lot of people think it's maximum permitted.

the OSG does funny things to a lot of people.

Click to expand...

Steps you are correct it's from osg 0.8 so is the dno max different

I'm sorry,,, but I'd be ringing up the DNO (24hr) emergency line with it being almost double the value they'd like it to be

Ampsyaman said:

Steps you are correct it's from osg 0.8 so is the dno max different

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They make their own rules,

But, as Noz says, ring them, once you have double checked it with another meter of course, 

It's unacceptably high, 

just call the emergency number and await your new PME supply. 

I will be re checking it in the week first thing, customer has said they were doing some sort of work at sub station or In the street few weeks back, grabbing another meter off my mate to double check don't want red face syndrome, gonna do best of 4 tests to double check make sure I've got consistent readings the same,  

Just a thought...when was your meter last checked ( calibration)?

did you Zero it first?......my 1654 has to be zeroed

just a thought

Ampsyaman said:

Steps you are correct it's from osg 0.8 so is the dno max different

Click to expand...

0.35, 0.8 for a 100A supply, are defined in 'Engineering Recommendation P23', not necessarily maximum values allowed.

I bet you they will say its not there problem, they don't have to supply  an earth &  they never fitted clamps so its a 'DIY' job  as they have never supplied an earth to that property.

call their enquiry line first and ask what earthing system it is

The 0.35 and 0.8 figures are not law, BUT they are a sort of generally accepted [by the DNO's] maximum. They point out that sometimes these figures may be exceeded, by a smallish margin, but 1.78 would not be right.. They will tell you that you have to provide your own earth. This is rubbish, the ESQCR is perfectly clear, where the DNO provide an earth, they HAVE to maintain it. This is statute law.. Do not let them say otherwise...

john..

If the measured Ze has risen from what it was a couple of weeks ago then it is not right, whatever the actual reading is it shouldn't vary very much without something changing in the supply. 

kerching said:

Just a thought...when was your meter last checked ( calibration)?

did you Zero it first?......my 1654 has to be zeroed

just a thought

Click to expand...

I'm going round with my fluke 1654 as I have only just purchased it it's brand new and calibrated by sis when purchased, plus Ze, test was done with my good old faithful kewtec kt in calibration, was not fully conversant with the 1654b but it will be having it next week been using it at my house to get used to it. it's way more in depth than my kt

On an earlier note I've seen the earth is bonded to the lead sheath leaded on

to it, no clamp, I meant I'd put my meter clamp on the lead sheath to see if I could get a better reading but it was still the same,

So the fluke has to be zero with the adaptor even for ze, thought that was only for dead continuity testing, does it hold the zero or is really zero on every use kerching, 

OK guys not updated been busy, the Dno come out, there readings were 1.09 and said somethings wrong, lol. There meter was questionable  plus had to borrow some batteries to run it,  said they need to do more diagnostics  as it could be the tap off joint or something more serious, so still waiting off customer now as to what they are doing, but was comments about digging up stuff,

OK guys not updated been busy, the Dno come out, there readings were 1.09 and said somethings wrong, lol. There meter was questionable  plus had to borrow some batteries off customer  to run it I couldn't be there at the time,  said they need to do more diagnostics  as it could be the tap off joint or something more serious, so still waiting off customer now as to what they are doing, but was comments about digging up stuff,

OK guys not updated been busy, the Dno come out, there readings were 1.09 and said somethings wrong, lol. There meter was questionable  plus had to borrow some batteries to run it,  said they need to do more diagnostics  as it could be the tap off joint or something more serious, so still waiting off customer now as to what they are doing, but was comments about digging up stuff,

Ampsyaman said:

So the fluke has to be zero with the adaptor even for ze, thought that was only for dead continuity testing, does it hold the zero or is really zero on every use kerching, 

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Why would it only be for dead testing? Do you not understand why leads are nulled (zeroed)?

nulling of leads is a useful facility whereby you can measure and store the resistance of the test leads in the meter so that the result displayed is actually the measured resistance minus the resistance of the leads. In years gone by you would have measured the resistance of the test leads, and then measured the resistance under test (including the tests leads) and then calculated the actual resistance under test by deducting the resistance of the test leads from the test measurement. 

Obviously the modern electrician is incapable of such simple mathematics so the meter does it for us.

So any measurement of resistance where the resistance of the test leads could alter the results requires some sort of nulling of the leads.

And a loose probe can spoil your day as well!

just saying