Very Hi ZS Reading on TT system? any advice

[srl-8]

We i am trying to understand, I have carried out a good few ZS test and up until now they were all fine results... Your right I dont know it all, I want to learn.. I am trying ti understand these results... thats why I have come on to this forum..

 

[GLENNSPARK]

the lowsst impedence path.....

 

[GLENNSPARK]

We i am trying to understand, I have carried out a good few ZS test and up until now they were all fine results... Your right I dont know it all, I want to learn.. I am trying ti understand these results... thats why I have come on to this forum..

basically you have a means of earthing here that can have a max of 1667 ohms....but a Ze of over 200 ohms may not be stable...in worst case conditions.....you aint gonna get a Zs of of any final circuits here anything like a tn system and you may also find that you are relying on an RCD soley for fault protection....

 

[mechelec]

We i am trying to understand, I have carried out a good few ZS test and up until now they were all fine results... Your right I dont know it all, I want to learn.. I am trying ti understand these results... thats why I have come on to this forum..

We never stop learning and NO-ONE knows it all. That said you are being employed by a customer for your knowledge and ability to carry out a safe and reliable installation and as such you need to know what you are doing. You clearly have a basic knowlege of the need to test but no understanding of how to interpret the results.
As a matter of interest you believed that the readings for Zs were above those quoted in the on site guide, what did you do about it? as your belief was it was unsafe. I bet it was left connected until you could get on this forum to find out what to do.

Not meaning to beat the same old drum or insult you but I hazard a guess that you have recently joined a Part P scheme after completing a short course.

 

[Specialist]

srl-8: None of us know it all & that's not what wer'e saying, but at the end of the Day the Public are paying for you to go into their property & carry out a Board change or whatever & expecting you to be fully competent at what your doing. From your post it appears that although you seem to understand basic testing, you don't understand the results you get & what to do about them. Not to put too fine a point on it but you could be risking peoples Lives & Property.

 

[GLENNSPARK]

We never stop learning and NO-ONE knows it all. That said you are being employed by a customer for your knowledge and ability to carry out a safe and reliable installation and as such you need to know what you are doing. You clearly have a basic knowlege of the need to test but no understanding of how to interpret the results.
As a matter of interest you believed that the readings for Zs were above those quoted in the on site guide, what did you do about it? as your belief was it was unsafe. I bet it was left connected until you could get on this forum to find out what to do.

Not meaning to beat the same old drum or insult you but I hazard a guess that you have recently joined a Part P scheme after completing a short course.

yes and if that is the case (a short part p course)...then it need addressing as were talking disconnection times here and these "courses" really should be covering this......

 

[mechelec]

yes and if that is the case (a short part p course)...then it need addressing as were talking disconnection times here and these "courses" really should be covering this......

They should, but in all honesty 5 weeks does not give you any time to learn the theory behind how we get the results we get and the reason for the tests being required. I have no doubt that testing is briefly covered but it takes time to teach it to people who in many cases have had no or very little past electrical experience.
There is no substitute to working with an experienced electrician and learning the ropes over time combined with theory based learning in college before going out alone.
Now what did they call that type of training that had worked for years and was proven to produce (mostly knowlegable) sparks and weeded out the dead wood and chancers (answers on a post card please)

 

[srl-8]

some info for you all.
1) yes I am part P
2) the property is my own, no customer life or money at stake
3) I came here looking for advice and help.
4) system left unconnected until i solve the problem.

So, who wants to answer my question straight? Please..

ZE reading 187ohm

I can determine ZS by enquiry, ZE +R1 +R2 = ZS

However, i tried to test and measure ZS at the end of the circuit and got these high figures of 2.6 2.5 etc etc...

again, any ideas on how to solve this issue???

Thanks

 

[IQ Electrical]

some info for you all.
1) yes I am part P
2) the property is my own, no customer life or money at stake
3) I came here looking for advice and help.
4) system left unconnected until i solve the problem.

So, who wants to answer my question straight? Please..

ZE reading 187ohm

I can determine ZS by enquiry, ZE +R1 +R2 = ZS

However, i tried to test and measure ZS at the end of the circuit and got these high figures of 2.6 2.5 etc etc...

again, any ideas on how to solve this issue???

Thanks

It's Ra, not Ze on a TT system.

Is your TT system protected by an RCD as it should be with that Ra value?

What is the rating of the RCD?

 

[srl-8]

ZE was 187

the system is protected by a 30ma RCD from the main house, and the new board is also protected by a 30 ma RCD.

??

 

[Simlec]

This is going to be a very long thread me thinks! :rolleyes4:

 

[One_of_them]

if your R1+R2 readings came back as satisfactory then that circuit impedance should be OK. Therefore you need to start looking at other factors relating to this issue i.e your Ze!! Are you earthing conductors connected correctly and secure and in good condition?

Get another rod sank in and see if this is any better to lower your Ze

 

[Specialist]

Discrimination ? i.e is the RCD feeding it in the House a time delayed type.

 

[IQ Electrical]

ZE was 187

the system is protected by a 30ma RCD from the main house, and the new board is also protected by a 30 ma RCD.

??

Ok then your maximum allowed Zs reading for each 30mA protected circuit is 1667 Ohms, problem solved in 31 posts.

Your RCD at the supply end should ideally be an 'S' type time delayed to achieve discrimination with the RCD at the remote end but I wouldn't loose sleep over that one.

 

[Richard]

ZE reading 187ohm

I can determine ZS by enquiry, ZE +R1 +R2 = ZS

However, i tried to test and measure ZS at the end of the circuit and got these high figures of 2.6 2.5 etc etc...

again, any ideas on how to solve this issue???

Thanks

ok, first it's not an issue.

When you tested Ze, You disconnected the earthing conductor which went to the earth rod I imagine.

As previosuly mentioned, you may well have bonding in place to the Water service???

Try testing with the earthing conductor re-connected, and you will probibly get a reading of somewhere around 2 ohms. As previsouly stated by telerix, by connecting the water pipe you've effectivly got a much better earth rod!

With regards to the values in the Regs - Being a TT system, because your Ze is not garenteed stable, circuits must be protected via RCD (in your case 30ma), which from what you say they already are.

 

[mechelec]

ZE was 187

the system is protected by a 30ma RCD from the main house, and the new board is also protected by a 30 ma RCD.

would that be a 30mA RCD protecting the sub main and another 30mA RCD protecting the final circuits in the outbuilding i.e. 2 RCD's in series

I was too slow in replying to specialist (too slow, specialist beat me) sorry to cause confusion

 

[IQ Electrical]

I'm busy writing an FAQ on TT systems for a certain organisation, judging by some of the questions (and answers) on this thread, I need to write faster!

 

[GLENNSPARK]

and if you are going to start driving more rods in...then go for depth every time ...."depth is the key with TT".....

 

[GLENNSPARK]

ZE was 187

the system is protected by a 30ma RCD from the main house, and the new board is also protected by a 30 ma RCD.

would that be a 30mA RCD protecting the sub main and another 30mA RCD protecting the final circuits in the outbuilding i.e. 2 RCD's in series

too slow, specialist beat me

i can feel discrimination entering the fray here!!..lol....

 

[Geordie Spark]

and if you are going to start driving more rods in...then go for depth every time ...."depth is the key with TT".....

Now THAT could have been posted by our good Friend E54 !!