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Topic Title: Help needed
Topic Summary: Old farm house
Created On: 17 January 2013 05:54 PM
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 17 January 2013 05:54 PM
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brian1962

Posts: 182
Joined: 06 May 2007

In the loft all day ! dirty, dusty and full of fibreglass. can any body help with an high Zs ? Mines a megger1553, it was showing 10.8v so hopefully not the meter playing up. It's TNCS was TT, It has 2 boards, looks like the rear extension is al on the new board, anyway come to test my downlights in the bathroom and it's reading is > 1.47k ohms. On RCD test auto it reads > 25v so it didn't operate the RCD. Had a look at most of the switches and fittings i could get to and the same readings, all except the extension and a small room above the fuse boards which are seperate, they have good readings, the one i may take my suupply to reads 0.70 ohms. The meter also flashed 255v for a few seconds then went to 228v then i did the Zs test to reveal > 1.47 k ohms, any help would be appreciated tonight before i go back tomorrow for a better look, what is annoying is all the diy lights that are up ! no certs anywhere and it's all free at the moment, i could just take my feed from the good circuit and mention the problem !!
 17 January 2013 05:55 PM
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brian1962

Posts: 182
Joined: 06 May 2007

Ze is 0.23 and the RCD works fine at source.
 17 January 2013 06:04 PM
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OMS

Posts: 18919
Joined: 23 March 2004

You say it's a TT converted to TN-C-S - it is actually connected to the means of earthing I take it (the board from which these high Zs circuits emanate from)

Failing that you've lost an earth somewhere along the way.

What does an earthed wander lead for continuity show up ?

Regards

OMS

-------------------------
Failure is always an option
 17 January 2013 06:06 PM
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slittle

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It's got to be a broken or no cpc in the lighting circuit from the old board hasn't it ?

Stu
 17 January 2013 06:16 PM
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brian1962

Posts: 182
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I'm getting 230v at the fitting between L & E
 17 January 2013 06:19 PM
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OMS

Posts: 18919
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Is there any bonding ?

Have you checked IR N-E

Regards

OMS

-------------------------
Failure is always an option
 17 January 2013 06:27 PM
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brian1962

Posts: 182
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I'll take the wonder lead tomorrow, but with getting 230v L & E at the last fitting ,it's thrown me. I found loads of bad earth connections around the house but not one of them made a difference. Quite alot of fittings are made up of a bit of flex coming from the ceiling !! I'll tell the customer tomorrow i cant certify it from this circuit and see what they say.
 17 January 2013 06:32 PM
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brian1962

Posts: 182
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It went thru my mind about N-E but would that not pull the RCD ? No more checks than Zs, because the paid for work was going backwards ; )
 17 January 2013 07:54 PM
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slittle

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Brian,

Just a thought, if you were measuring at the fitting with the megger it probably will read 230 L&E even with 1.4k Zs.

Try either the screwdriver in the garden trick and measure the cpc to that or with it all dead, take the Live out of the mcb and stick it in the earth bar and measure L-E at the fitting on ohms range.


Stu
 17 January 2013 11:21 PM
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AJJewsbury

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I'm getting 230v at the fitting between L & E

With no current flowing, you'd get that even if the c.p.c. has a resistance of several meg ohms to earth (provided the L-c.p.c. resistance was still significantly higher). My first guess is a very bad (but not perfectly insulating) joint in the c.p.c..
- Andy.
 17 January 2013 11:36 PM
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rocknroll

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Originally posted by: slittle

Brian,

Just a thought, if you were measuring at the fitting with the megger it probably will read 230 L&E even with 1.4k Zs.

Try either the screwdriver in the garden trick and measure the cpc to that or with it all dead, take the Live out of the mcb and stick it in the earth bar and measure L-E at the fitting on ohms range.

Stu


I remember in the 80's an electrical distributor when they found out electricians were going to the local auto stockist to buy a screwdriver for this purpose ordered a box full from Draper or somewhere and they went in two days, it was called the 'Mini bottom-hose' screwdriver at about a metre long in both flat and crosshead. LOL

I bet BOD has still got one!!!

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 17 January 2013 at 11:51 PM by rocknroll
 18 January 2013 01:25 PM
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brian1962

Posts: 182
Joined: 06 May 2007

Thanks for the replies, i will try again next week. never tried the screwdriver trick, will give that a try ! I told her all this on the phone last night and asked her what she wanted to do. I will put my new feed to the downlights on the good circuit and fill out the certificate with the fault on for her and anybody else to see. It needs a EICR doing, i'm sick of working for nothing ! half a day yesturday taking switches and pendants down, she tells me now it's had lots of different sparks over the years and i am the first to talk about certificates !! I have learnt one thing thou 230v L -E even thou it's a bad earth, i must admit i took that for granted as ok ,years ago.
 18 January 2013 07:12 PM
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GJH

Posts: 495
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You should charge the customer extra Brian, i know its difficult sometimes but these are faults that need rectifying and the customer should pay for that half day at least! Its not your fault.
 18 January 2013 07:25 PM
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perspicacious

Posts: 7031
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"I bet BOD has still got one!!!"

No, believe it or not, it was the heater bypass hose on the cylinder head that caused me issues during 1976 on my Mini van

But, I feel I've let you down, so I'll have to get on a popular internet auction site to buy one..................

Regards

BOD
 18 January 2013 07:42 PM
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rocknroll

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regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
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