Ze-Zs-Zdb

[DeanoRN]

Hi all,

just a quick question, i'm currently learning how to test different installs, I have been testing houses and obviously it's easy to get to the service head and determine what earthing arrangement etc and also taking Ze from the consumer unit ect, but when testing Ze in an environment where you cant get to the service head do you still record Ze from the consumer unit or will that be recorded as Zs? also if there is a KMF switch should you take your Ze reading from that instead of the consumer unit?

cheers
Deano

 

[gazdkw82]

If it's a sub board I'd record it as Zdb.

Zs is generally for final circuits

 

[westward10]

Zdb is not an official term although frequently cited. Ze means impedance external at the source of supply, anything else is Zs, impedance of the system.

 

[ruston]

Zdb is not an official term although frequently cited. Ze means impedance external at the source of supply, anything else is Zs, impedance of the system.

You are correct , ZDB was cited by a member of the IET forum years ago and stuck , it was used on other forums subsequently at the time and has become widely used.
At least that is how I remember it.
It was debated on the IET forum at the time.

 

[Andy78]

Zdb sometimes appears on certs, but it should be remembered as Zs@DB, as it is the Zs of the circuit supplying that DB.

Ze is always measured at the origin of the install, at the point of the installation closest to the origin. If that point is at a KMF switch then that's where you take the reading.

Where you can't get access to the origin to measure Ze then it can't be recorded and a Zs@DB is not a substitute

 

[gazdkw82]

when I did 2391 I was Zdb was acceptable on any forms/test sheets