Ze, R1+ R2 and Zdb

This is related to domestic really

So you have the supply into an isolator then on to two consumer units

from the diagram..

Ze is at the origin ( Isolator) with the means of earthing disconnected.

This supply Cable to the DB's what test on it would you perform on an EICR

Now. on an EICR for example should I take a measurement of the R1+R2 of the cable feeding DB1 and DB2
If this was a new install and initial verification you would take your R1+ R2 and R1 + RN of your cable feeding the DB's prior to energising, but on an EICR I presume you would not disconnect to test this supply cable between the isolator and DB1 and between DB1 and DB2


When doing Zdb (basically Zs) at the two DB's, All earthing remains connected (Earthing conductor, bonding etc.)

And technically the earth connection between the met and the DB is a CPC, to an earth marshalling point.

You only have one earthing conductor which is the means of earthing to the MET. i.e the connection from the supply sheath, or TNCS

Hope that make sense.


Sorry slight mistake in the drawing, when doing the Zdb the isolator will be on !!

I'd Test R1+R2 between the Isolator to DB1 (most likely 0.01 if close) if they're singles then not much point doing IR, at DB2 the same though is it Fed from a Fuse inside DB1 or the same isolator with Two outgoing cables?

studentspark said:

Ze is at the origin ( Isolator) with the means of earthing disconnected.

Click to expand...

Yes Nothing connected to the supply earth.

This supply Cable to the DB's what test on it would you perform on an EICR

Click to expand...

I suppose you could do an end to end to check if relation of conductors is as expected - but as below, I don't think they should be disconnected.

Now. on an EICR for example should I take a measurement of the R1+R2 of the cable feeding DB1 and DB2
If this was a new install and initial verification you would take your R1+ R2 and R1 + RN of your cable feeding the DB's prior to energising, but on an EICR I presume you would not disconnect to test this supply cable between the isolator and DB1 and between DB1 and DB2

Click to expand...

That can be calculated from the end to end measurements. I would not disconnect.

When doing Zdb (basically Zs) at the two DB's, All earthing remains connected (Earthing conductor, bonding etc.)

Click to expand...

Yes - to determine the actual situation.

And technically the earth connection between the met and the DB is a CPC, to an earth marshalling point.

Click to expand...

Yes, although the MET might be in the first DB.

You only have one earthing conductor which is the means of earthing to the MET. i.e the connection from the supply sheath, or TNCS

Click to expand...

Yes.

Sorry slight mistake in the drawing, when doing the Zdb the isolator will be on !!

Click to expand...

Ok. I don't think the middle diagram would ever be applicable.