why enquire about ze

[johnboy6083]

in the electricians design guide, you can get the impedance values for common sizes of supply transformers. Also on most industrial sitesthat are fed direct from a Tx, the cable size and run is known, and can be used to give accurate impedance values. This can then be used to calculate fault currents.I would work with worst case scenario, which is a short across phases, on an unloaded large capacity system.

 

[Sparky Ninja]

cheers lads but on the dvd it was a domestic installation just thought it was strange why not test it yourself

The NICEIC are waving the flag for Regulation 14 of the EAWR. Many times in their publications and videos they push the idea of calculating Ze's, Zs', pfc's.
BS 7671 states that these values can be obtained by enquiry or measurement, whilst the EAWR states we can only work live if it is impracticable not to do so. So, by elimination they suggest enquiry should always be used for EAWR compliance.

A load of crap if you ask me.

 

[Farmelectrics]

why is the eicr asking for zs top of page 5 shouldnt it be zdb then

 

[Sparky Ninja]

why is the eicr asking for zs top of page 5 shouldnt it be zdb then

NICEIC wanted the terminology Zdb introduced, but JPEL/64 concluded to refer it as Zs at db.

 

[telectrix]

it is crap, widdler. live testing is not the same as live working. maybe niceic need to use a dictionary. i know what i prefer. enquiry will usually get yo answers ranging from " ain't got a clue" to it's "0.35 or 0.8 depending on the type of earthing, and the bloke who knows that is off sick/on holiday/taking his cat to the vet"

 

[ian.settle1]

Whats the point in enquiring as all the DNO will quote is the values in the regs.

 

[Farmelectrics]

widder whats jpel/64

 

[Farmelectrics]

widder your correct niceic dont like doing live test they tell you to calculate them well they do on dvd but by calculation you will allways get a higher zs reading than your r1 r2 and thats not allways the case so yes its a bit like guessing

 

[Darkwood]

on a slight different tangent ... but in answer also to OP, new installs are sometimes designed before the building is even there so an enquiry is needed to give guidance on the installation design, and other situe is empty new build with sealed cutout and on the same lines is having a electrical system designed on say CAD.

 

[GLENNSPARK]

widder your correct niceic dont like doing live test they tell you to calculate them well they do on dvd but by calculation you will allways get a higher zs reading than your r1 r2 and thats not allways the case so yes its a bit like guessing

well a measured Zs will often be lower than an R1 R2 due to parallel paths.....i like to get a measured value of Ze and Zs but its a case of theres more than 1 way to get a value to put on a cert but theres also 10.3.7 in the OSG that says:
It is not recommended that installation designs are based on measured values of prospective fault current as changes to the distribution network subsequent to completion of the installation may increase fault levels....

 

[Risteard]

why is the eicr asking for zs top of page 5 shouldnt it be zdb then

The problem with the form stating Zdb is that technically there is no such thing. It is simply the Zs at that point. Zdb is slang rather than correct terminology.

 

[telectrix]

Whats the point in enquiring as all the DNO will quote is the values in the regs.

that's if you actually get to speak to someone who actually has a clue what you are talking about.

 

[telectrix]

The problem with the form stating Zdb is that technically there is no such thing. It is simply the Zs at that point. Zdb is slang rather than correct terminology.

and there's me thinking it was an abbreviation for zebedees

 

[GLENNSPARK]

at least with the definition of Zdb when looking at any previous schedules....you know immediately its for a sub-board....

 

[Farmelectrics]

Thanks for your thoughts lads as I say great forumn this never stop learning