Discuss Advice on testing Ze please....... in the Electrical Forum area at ElectriciansForums.net

Baddegg

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As per a couple of previous threads am now at first fix stage and am thinking about testing,
Set up is tn-s,main income tails split through Henley into switch fuse isolater and 10mm 3 core sea out to (approx 20mtrs) Cu unit in man cave/pub
Never tested a unit so far from the origin that wasn’t a sub db, questions are is this still considered a sub board? Am I right in thinking I need to take ze at the origin before switch fuse isolator? As to take it at the Cu is not external? And if so what would I record on the sheet for the swa feeding the unit?
Hope that makes sense?
Thanks in advance as always
 

Andy78

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A reading at the CU would be the Zs of the distribution circuit feeding that CU.
A Ze is taken at the origin with the installation isolated and all parallel paths removed.
 

Grezza

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The CU feed is a final circuit so as above, remove all PP and test at incoming.

I’d also test at the CU and record as a Zdb and note where it was taken from.
 
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Baddegg

Baddegg

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Thanks chaps, I’m fine with ze at origin etc just with why the shed Cu becomes a final/distribution circuit as opposed to a normal Cu,is it just because it’s more than 3 mtrs and the isolator has been introduced?
 

Andy78

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Thanks chaps, I’m fine with ze at origin etc just with why the shed Cu becomes a final/distribution circuit as opposed to a normal Cu,is it just because it’s more than 3 mtrs and the isolator has been introduced?
Any loop reading within the consumers installation will be a Zs, be it at the end of a final circuit or distribution circuit. I'm not sure what you mean by "normal CU" and how any other CU would differentiate with the one in this shed.
 

Archy Styrigg

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Is the CU in question fed from the Switch fuse? If not, surely it needs some protection being >3m.
Where do the other tails go to?
 
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Baddegg

Baddegg

Still simmering Ken, not boiled yet buddy x
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Hi Archie yes unit in question is fed from the switch fuse,the other tails go to the Cu in the house as per original set up
 
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Baddegg

Baddegg

Still simmering Ken, not boiled yet buddy x
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Sorry Andy, I’m starting to confuse meself here,normal Cu being any standard household unit less than 3 mtr tails, where you’d take your ze as per normal, I’ve tested sub db’s before that have been feed through an mcb on the household unit and understand why they are considered final circuits, as this setup (the unit in the man cave) is on its own after the switch isolator it’s caused me to think a bit more about I how I record my readings and where I take them from,
 

Andy78

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Sorry Andy, I’m starting to confuse meself here,normal Cu being any standard household unit less than 3 mtr tails, where you’d take your ze as per normal, I’ve tested sub db’s before that have been feed through an mcb on the household unit and understand why they are considered final circuits,
Not half as confused as I am.

Back to original post

Never tested a unit so far from the origin that wasn’t a sub db, questions are is this still considered a sub board?
Any circuit that feeds a distribution board is a distribution circuit.
 

ChrisElectrical88

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Ze at Origen.
Zdb at Dist Board.
Switch fuse to be treated as its own board on the certificate. Dist board will be the circuit from this switch fuse so R1+R2 IR etc will need to be taken on the sub main.

If that makes sense
 

ChrisElectrical88

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So on your Circuit schedule your circuit will be call for example 'Submain to DB - DB1' and filled out and tested as any other circuit.
 

Murdoch

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Interesting read ....... so the origin is the DNO fuse? No - so the Ze to be taken at the Henley block?
 
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Baddegg

Baddegg

Still simmering Ken, not boiled yet buddy x
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i was just pondering that very question Murdoch.....
 

Murdoch

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Nearest place to the cut out as reasonably practical.
I was taught a Ze was taken at the cu or switch fuse ... if the cu has one
 

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