Zs at db

[torrens75]

Hi all,

I have my 302 practical tommorow, and feel confident, but just one thing if i may.

Zs at db, as far as i was aware Zs is measured at the furthest point of each circuit and recorded on the schedule of test result against that circuit.

How and why is Zs db measured?

 

[KAS1]

You mean Zdb not Zsdb

- - - Updated - - -

Zs is at the furthest point

 

[SirKit Breaker]

You are getting mixed up mate.

Zdb is taken at the second and subsequent Dist boards in the installation.

If you have one DB supplying your installation, like in a domestic house, you would take Ze at the supply origin.
You would then take Zs at the extremity of each circuit as you say.

If the circuit was a submain supplying another DB in say an outbuilding, then you would take Zs at this DB, and record it as Zdb, so in effect, your Zs becomes Zdb if it is a distribution circuit to another distribution board.

Cheers...........Howard

 

[Sintra]

Zdb is used as an alternative for Ze. This is when for operational reasons on periodic testing the main earthing conductor can not be disconnected or the installation isolated.

 

[torrens75]

Why does it say Zs db @ top left hand corner of test results sheet???

 

[Farmelectrics]

I'm with circuit breaker

 

[KAS1]

Post No 3 has explained this

 

[torrens75]

You are getting mixed up mate.

Zdb is taken at the second and subsequent Dist boards in the installation.

If you have one DB supplying your installation, like in a domestic house, you would take Ze at the supply origin.
You would then take Zs at the extremity of each circuit as you say.

If the circuit was a submain supplying another DB in say an outbuilding, then you would take Zs at this DB, and record it as Zdb, so in effect, your Zs becomes Zdb if it is a distribution circuit to another distribution board.

Cheers...........Howard

Ok, it does say Zs at DB (Ohms) - So, to confirm, I take it as if I am testing, like you say at DB in the garage, the Zs at DB is the Zs at the main switch of the DB in the garage ( taken at main switch, incoming phase, incoming neutral and earth? ( treating the DB in the garage as a circuit so to speak, with the db being the extremity of the circuit?

Hope that makes sense!!

 

[brucelee]

YEs Its basically your Zs of the circuit from main board and its also the Ze of that board then when you add that to your R1 +R2 of the final circuit thats your Zs

Ze + main board Plus R1+R2 sub main is your Zs of that circuit and the Ze of the Sub board

so for every board you would fill in seprate schedule of test results and resord the Ze for the main board on the EIC and on the first schedule of test results then when you have calculated or measured your Zs of the sub to the garage ccu RECORD THAT AS THE ZS AT THIS BOARD IN THE TOP CORNER
Zs = Ze Origin + (R1 +R2 sub main ) + (R1+R2 final circuit )

 

[Brightspark2]

Zdb is used as an alternative for Ze. This is when for operational reasons on periodic testing the main earthing conductor can not be disconnected or the installation isolated.

I'm with this guy...


Zs at a DB is just that, a Zs...

 

[sparkymalarky]

Zdb is not always an alternative for Ze. Ze is either measured/enquired about​ or its not. I carry out EICR's on installations in excess of 500 circuits every week so obviously multiple distribution boards. A Distribution Board supply is a circuit with an earth fault loop impedance reading. I understand some refer to it as Zdb but I just don't

 

[Engineer54]

Zdb is not always an alternative for Ze. Ze is either measured/enquired about​ or its not. I carry out EICR's on installations in excess of 500 circuits every week so obviously multiple distribution boards. A Distribution Board supply is a circuit with an earth fault loop impedance reading. I understand some refer to it as Zdb but I just don't

It's a term that's been used for donkey's years, and eases confusion with Zs values for final circuits!!

 

[sparkymalarky]

It's a term that's been used for donkey's years

I'm quite aware of what it is E45! I just don't see the where the confusion lies when testing a domestic property with one DB. lol.Still, its referred to and recorded as Zs at DB in BGB. So personal preference really. lol

John

 

[Engineer54]

I'm quite aware of what it is E45! I just don't see the where the confusion lies when testing a domestic property with one DB. lol.Still, its referred to and recorded as Zs at DB in BGB. So personal preference really. lol

John

Errrr, you don't use the term Zdb on a single CU/DB installation, you'd use the Ze value!! The term is only used where there is MORE than one CU/DB!!

 

[sparkymalarky]

My bad, explained myself poorly there! Well I don't see the need to use it at all!