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loop impedence on a tt system


 
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unclebubble

from United Kingdom

Joined: 15 Jun 2007
Posts: 31
Location: United Kingdom

PostPosted: Tue Oct 02, 2007 5:09 pm Reply with quote

This is the first time I've done a test on a TT system and I'm a bit stuck on the readings I am getting for loop impedence.
My Ze reading is 9.7 ohms which I think is ok(pretty sure I'm reading regs ok saying 21 ohms max)
The only thing is every reading I am getting from every circuit be it the end of the line or not is 2000 ohms.Its like it reads it and it just keeps giving me that.I am testing with a Fluke tester and there is no way to change the loop setting.
Now do I need to get another loop impedence tester with a setting selector or as I'm reading the regs---having a 100ma RCD protecting every circuit(as impedence reading is so high)is ok and I can just leave the readings I'm getting and write those down(this is a periodic inspection and report)
Any help would be great as NICEIC help line not much assistance thanks!
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GaryMo

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PostPosted: Tue Oct 02, 2007 5:15 pm Reply with quote

If you have a Ze reading of 9.7ohms then why aren't you getting an earth fault loop impedance reading?
What are your R1+R2 readings?

If your R1+R2 readings and Ze test out OK then I would look at borrowing another meter.
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Albert

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PostPosted: Tue Oct 02, 2007 5:21 pm Reply with quote

sorry I do not have much experience testing TT but have with the Fluke, when toy read in continuity 2000 ohm means no continuity. Normally Zs is a live test so the meter will buzzz if ther is no power. As mentioned above I would check again continuity.[/code]
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unclebubble

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Joined: 15 Jun 2007
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PostPosted: Tue Oct 02, 2007 5:30 pm Reply with quote

Yeah the installation is energised and working.I haven't done R1+R2 yet it would be a be unreal that every circuit had bad continuity(I know its poss!)
There are 15 circuits on this board so the house is large!One circuit I have just put in is a shower and it is still reading 200 ohms(I have done R1+R2 on this circuit its fine)The tester is telling me I have L N E and it beeps like it normally does when I do a test!I know TT systems are quite rare so I'm well confused perhaps I should just get another meter!!
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GaryMo

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PostPosted: Tue Oct 02, 2007 5:47 pm Reply with quote

Forget it being TT, it won't matter.
You have a Ze of 9.7ohms and an acceptable R1+R2 reading on your shower circuit (out of interest, what was the reading?) so you should see a healthy Zs reading. If not then it's the meter at fault.
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plugwash

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PostPosted: Tue Oct 02, 2007 6:02 pm Reply with quote

where exactly are you taking your Ze reading from?

It sounds to me like there is a fault between where you are taking your Ze reading from and the earth bar of the CU.
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fireman22

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PostPosted: Tue Oct 02, 2007 11:09 pm Reply with quote

what model fluke is it???
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securespark

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PostPosted: Wed Oct 03, 2007 4:14 am Reply with quote

Are you SURE that Ze reading is taken correctly?

Switch the CU isolator off.

Disconnect the main earthing conductor from its terminal.

In effect, you should now have a live, neutral and earth that are not connected to anything.

Now test your Ze from these.

What is the reading now?
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unclebubble

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PostPosted: Wed Oct 03, 2007 6:04 pm Reply with quote

Yep I've done everything that everyone suggested the first time around.I am doind the Ze at source(consumer unit)connected and un connected my earth stake is fine I'm getting 63 ohms.
I'm going back tomorrow to try and see if I can solve this prob I'll keep you all posted!
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fireman22

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PostPosted: Wed Oct 03, 2007 10:59 pm Reply with quote

fireman22 wrote:
what model fluke is it???
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Paul Barker

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PostPosted: Thu Oct 04, 2007 6:14 am Reply with quote

unclebubble wrote:
Yep I've done everything that everyone suggested the first time around.I am doind the Ze at source(consumer unit)connected and un connected my earth stake is fine I'm getting 63 ohms.
I'm going back tomorrow to try and see if I can solve this prob I'll keep you all posted!


Then ze is 63 ohms plus you might have a good meter and a bad main earth conductor.
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