Garage cu

[Gary latto]

Hi all from an old git still learning and hoping to do 2391 some time soon,
If doing a ze on my garage cu do I do it as a zs ?
since its fed from cu in main house do I treat it just like doing a zs and then does it become a zdb ??
Thanks all ?

 

[westward10]

It will be Zs no such thing as Zdb.

 

[Gary latto]

It will be Zs no such thing as Zdb.

Cheers for reply ? so just do as a zs and compare to table for size and type of mcb ?

 

[westward10]

Cheers for reply ? so just do as a zs and compare to table for size and type of mcb ?

Yep correct generally you only have Ze in one place, the source of supply. The garage CU supply is effectively no different to any other final circuit so Zs.

 

[Gary latto]

Yep correct generally you only have Ze in one place, the source of supply. The garage CU supply is effectively no different to any other final circuit so Zs.

Cheers for the info ?

 

[HappyHippyDad]

It will be Zs no such thing as Zdb.

Well I never, I was about to say if you look on the generic schedule of test results sheet you will see Zdb. Just had a look and it says Zs at DB. Right again Westy.

I like trying to find times when either you are @davesparks are wrong as it's so bloody rare!

 

[Ian1981]

It will be Zs no such thing as Zdb.

Actually zdb is now included on the model forms of bs7671 for the minor electrical works certificate
[automerge]1583411352[/automerge]

Well I never, I was about to say if you look on the generic schedule of test results sheet you will see Zdb. Just had a look and it says Zs at DB. Right again Westy.

I like trying to find times when either you are @davesparks are wrong as it's so bloody rare!

Zdb is included on the electrical minor works certificate on the model forms of bs7671

 

[westward10]

Is it actually on the BS7671 model form as it crossed my mind as you posted. It isn't listed in the abbreviation section.

 

[HappyHippyDad]

Actually zdb is now included on the model forms of bs7671 for the minor electrical works certificate
[automerge]1583411352[/automerge]

Zdb is included on the electrical minor works certificate on the model forms of bs7671

Get in there Ian, well done! @westward10 please check your facts before posting

 

[Ian1981]

Is it actually on the BS7671 model form as it crossed my mind as you posted. It isn't listed in the abbreviation section.

Yes In part 2 of the certificate Indent no 2
Earth fault loop impedance at distribution board (Zdb) supplying the final circuit

 

[HappyHippyDad]

Is it actually on the BS7671 model form as it crossed my mind as you posted. It isn't listed in the abbreviation section.

I only checked on the EIC where it says Zs at DB. The MWC does actually say Zdb.

 

[Ian1981]

Get in there Ian, well done! @westward10 please check your facts before posting

Sack him as moderator haha

 

[westward10]

I'm in the corner

 

[HappyHippyDad]

You know you're on to a winner in life when you're sat at home debating the validity of 3 letters

 

[Ian1981]

You know you're on to a winner in life when you're sat at home debating the validity of 3 letters

It’s the little things in life

 

[Andy78]

Hi all from an old git still learning and hoping to do 2391 some time soon,
If doing a ze on my garage cu do I do it as a zs ?
since its fed from cu in main house do I treat it just like doing a zs and then does it become a zdb ??
Thanks all ?

Z is impedance. The e stands for external, so it's the part of the earth fault loop impedance path that is external to the customer's installation. It can only ever apply to a reading taken excluding the customer's installation wiring.

Zs is earth fault loop impedance measured at any point in the customer's installation with the highest result recorded for a circuit.

As for the pedantry about terminology, BS7671 states Zs at db on the model schedule of test results, Zdb on the model minor works cert, but only mentions Ze and Zs in the table of symbols used in the standard.
So everyone is correct

 

[ruston]

It was used by a member of the IET forum years ago and just stuck .
I can't remember the name but he was a regular contributor.

 

[Risteard]

LOL. If the model forms contain the term "Zdb" then that is in my opinion a bad thing as it has never been a term recognised by the Regulations. It is the Zs of the distribution circuit.

 

[ruston]

ZDB or DB isn't in the definitions , symbols or abbreviations used in the standards of BS 7671.
As far as I can see anyway.

 

[davesparks]

I only checked on the EIC where it says Zs at DB. The MWC does actually say Zdb.

But are the model forms informative or normative?
As it doesn't appear in the list of definitions you're on pretty thin ground to start with.