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Cooker and high earth loop impedence test


 
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brock-cruse

from United Kingdom

Joined: 05 Aug 2007
Posts: 8
Location: Nottinghamshire,
United Kingdom

PostPosted: Sun Aug 05, 2007 7:43 am Reply with quote

Hi
Just looking for some info before i try and sort out an electrician!
Moved into new house 2 weeks ago with disgusting cooker (cleaned the hob so managed to use that while waiting for new cooker delivery but would not open grill or oven!).Well cooker arrived and included connection and disconnection of old cooker etc.
So old cooker using 10 mm cable instead of 6mm. Fitter said he could sort out but recommended changing. He then said that my cooker control panel should be within reach of cooker instead of in cupboard next to it (reasonable). However when he came to do final checks the earth loop reading came back at 14.76 (done twice) instead of should be about 0.8???? He checked our supply came underground which it did. Then he did say that it was taking soime time for his meter to show the reading so there maybe a problem with wiring. Hence he disconnected cooker, turned it off at the cu and recommended getting in an electrician. Texted hubby about this who then got a garbled story from a friend that he had similar problem and he has just sent off cheque to network services to come sort out? Is this something to do with the electricity board then?
Looking at my paperwork the fitter gave me (cos otherwise not got a clue!) he used a FLIUKE 1652 meter, my cooker is not protected by RCD has cicuit fuse MCB the earth return is direct and fuse rating 32amps, it passed the pre-installation polarity test. So is this going to be a big job for electrician?
Any info appreciated thanks
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Albert

from United Kingdom

Joined: 17 Feb 2004
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PostPosted: Sun Aug 05, 2007 8:24 am Reply with quote

As a start comment, if your cable is bigger than what is required I would not bother as it is not unsafe, unless you are rewiring anyhow. To know whether you should contact the LEB he should test the Ze (external loop impedance), the FLUK 1652 should be ok. It is nice to have a fancy tester but if someone does not understand the readings...?
You should know the earth arrangement (TN-S, TN-C S, TT etc.), because if you can not test the Ze you can use the maximum allowed;
TN-S = 0.8ohm and TN-C -S = 0.35ohm etc.
cooker control panel should be accessible and max. 2m away, it is not always possible to fit it near the cooker.
Testing the Ze or Zs and using 3 cables for the test (I have the FLUK 1653 and it is the same process), it is not instant and after pushing the test button it takes few seconds to get the result.
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Adam_151

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PostPosted: Sun Aug 05, 2007 5:35 pm Reply with quote

brock-cruse wrote:

So old cooker using 10 mm cable instead of 6mm. Fitter said he could sort out but recommended changing.

Nothing wrong with using a larger cable than actually required as long as it fits in the terminals

Quote:
He then said that my cooker control panel should be within reach of cooker instead of in cupboard next to it (reasonable)

Indeed reasonable, in the cupbaord is a daft place to put it

Quote:
However when he came to do final checks the earth loop reading came back at 14.76 (done twice) instead of should be about 0.8????

Not convinced he really knew what he was doing, but 14.76 is indeed too much if earth fault protection is by an overcurrent device, and 0.8 would be ok for protection provided by 32A B curve circuit breaker, or 30A re-wireable or cartridge fuse, his 0.8 figure possibly is from the 0.8 maximum Ze (thats earth loop at intake possition) for a TNS earthing system


Quote:
He checked our supply came underground which it did.

Supply earthing type is not as simple as overhead = TT, underground = TNS !, did he understand what he was doing?


Quote:
Then he did say that it was taking soime time for his meter to show the reading so there maybe a problem with wiring. Hence he disconnected cooker, turned it off at the cu and recommended getting in an electrician.


Did he check Ze? cos if its a high Ze thats casuing the high Zs then its not just the cooker circuit EEBADS isn't going to work for....


Quote:
Texted hubby about this who then got a garbled story from a friend that he had similar problem and he has just sent off cheque to network services to come sort out? Is this something to do with the electricity board then?


If its an out of spec Ze, then its upto the DNO to fix

Quote:
Looking at my paperwork the fitter gave me (cos otherwise not got a clue!) he used a FLIUKE 1652 meter

A popular all in one Con/Ins + loop + rcd tester

Quote:
my cooker is not protected by RCD has cicuit fuse MCB

What MCB? B3 or D63, it matters a lot icon_wink.gif (B32 is the norm)

Quote:
the earth return is direct

?

Quote:
and fuse rating 32amps,

fuse? MCB you mean? or cant he decide what it is icon_razz.gif

Quote:
it passed the pre-installation polarity test

Do you have a value for an R1+R2 test, or did he check it someother way? Ze value would be nice too icon_smile.gif

Quote:

So is this going to be a big job for electrician?


Depends what the issue is, it might not even be a job for an electrician at all!

P.S. A picture of the incommer, meter and Cu wouldn't go amiss icon_smile.gif
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securespark

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PostPosted: Sun Aug 05, 2007 10:19 pm Reply with quote

If the tester did a Zs, then polarity would automatically be checked at the same time.

You may well have subterranean TT. This looks like TN-S, but with no earth connection to the sheath.



As others have said - the Ze needs confirming, along with the supply type.

If you have TT, as long as you have the correct RCD protection, your Zs reading is acceptable. If you have a TN supply, it is not, but you need to know whether the poor reading is due to a dodgy installation or a poor connection at the origin. Hence needing the Ze figure. Also, you could get the ZS checked from other circuits. Chances are if you have several circuits with poor Zs readings, the Ze will be up the spout.

Thanks to RF Lighting for the piccy.
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brock-cruse

from United Kingdom

Joined: 05 Aug 2007
Posts: 8
Location: Nottinghamshire,
United Kingdom

PostPosted: Mon Aug 06, 2007 12:41 pm Reply with quote

Thanks all for your answers. I emailed my electric board last night about it and they are sending someone round today! Makes me think it may be serious!
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brock-cruse

from United Kingdom

Joined: 05 Aug 2007
Posts: 8
Location: Nottinghamshire,
United Kingdom

PostPosted: Mon Aug 06, 2007 7:23 pm Reply with quote

Hi
Well electricity board said that the earth was not connected! So ive called out a sparky who is coming tomorrow to check things out. Think the options are an earth rod or PME (plus hopefully will be able to sort out cooker).
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Adam_151

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PostPosted: Mon Aug 06, 2007 8:01 pm Reply with quote

For a TNC-S earth (PME) the DNO need to provide an earthing terminal for it, have they done this?

Or is it that the terminal there, but no one has connected anything into it?

A picture might be usful
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