2391 Practical ZS

[CRAGS]

For the 2391 Practical when you test the SP+N consumer unit for ZS and ZE which I am guessing is one test is it just L-E ???? Or do you do L-N as well I did make some notes last night but L-N does not seem right ???? Thanks in advance

 

[Guest123]

If your testing at the single phase board, which is a sub-main off the 3 phase board, then you are testing both Zs, and the PFC of that sub-main circuit.

Ze will only be measured at the incomming supply to the 3 phase board.

 

[CRAGS]

We were told to measure Zs for the single phase board (Record on three phase test sheet as Zs for SP +N) and record the same figure on the SP test sheet for the Ze.

But how do you do the test ???? I thought Zs for lighting or socket was live earth neutral but I am sure we only did live and earth last night

 

[Guest123]

Ok so on the main certificate for the 3 phase board, the sub-main to the single phase board will be one of the circuits so you record R1+R2, I/R, Zs etc.

On the continuation sheets that accompany the main certificate the single phase board becomes the main board if you like, with all of it's circuits then listed in the continuation schedules.

Usually (on NIC forms at least) at the top there are two boxes that are filled in when the CU is not connected directly to the origin, i.e a sub-board fed via a sub-main. In these boxes it asks for "chracteristics at this distribution board" this is where you measure the Zs or Zdb as it's also known and the PFC.

I find it funny that they would tell you that this should be recorded as a Ze value as it isn't.

Earth fault loop impedance can be measured using a two or three lead instrument, as can PFC.


Hope this helps.

 

[CRAGS]

He did mention about recording it as zbd. I think it is the way the boards are set up that he is telling us to record it that way???

I know how to do the pfc test I.e. L-N L-E

But what about the ZS can that be done on 2 lead by just L-E ???

Thanks again

 

[Guest123]

Yes...you only need L+CPC to carry out a Zs test. Some meters need the neutral connection to work is all.

Have you git a copy of GN3???

 

[CRAGS]

Yes got a copy of guidance notes 3 it just threw me that on the ceiling roses for Zs we were doing E-L-N and on the SP unit we were only doing L-E The meter is a megger 1502