PFC and ZE testing

[noidea]

Morning all
I am new to testing and electrics so if my questions are stupid and the answer obvious then I apologise, but we've all got to start somewhere.
I have been doing various electrical jobs around my home. Rewired the shower, cooker and central heating system. I have also rewired the ring main and lighting in the garage and installed a new CSU in the garage.
My 1st question is once I have taken one ZE reading for the shower for instance can I use this reading for all of the circuits I need to test?
Secondly, I am a little confused on the PFC test procedure. I believe I read somewhere that some testers will give you the PFC result at the same time as when the ZE test is performed. But I'm also under the impression that the main earth needs to be connected to do a PFC test and that according to GN3 this test should be performed
at every relevant point of the installation
Am I just wrong about the tester giving the ZE and PFC at the same time? The tester in question was either a Megger 1552 or a Di-Log 9083p

 

[LlandrilloSpark]

Morning

You wouldnt take a Ze reading for the Showers as such, you would take a Ze for the entire installation, GN3 tells you how to do this, basically it is taken at the DB with the Main Switch open, i.e installation shut down, and the main earthing conductor disconnected.

The Ze reading you get can be added to your (R1+R2) for each circuit to give you a Zs for each circuit.

Testing of an installation has many steps which have to be peformed in the correct order both for safety and also they rely on each other.

PFC is taken in the same place with the same instrument just change the setting on the tester.

 

[brucelee]

Morning all
I am new to testing and electrics so if my questions are stupid and the answer obvious then I apologise, but we've all got to start somewhere.
I have been doing various electrical jobs around my home. Rewired the shower, cooker and central heating system. I have also rewired the ring main and lighting in the garage and installed a new CSU in the garage.
My 1st question is once I have taken one ZE reading for the shower for instance can I use this reading for all of the circuits I need to test?
Secondly, I am a little confused on the PFC test procedure. I believe I read somewhere that some testers will give you the PFC result at the same time as when the ZE test is performed. But I'm also under the impression that the main earth needs to be connected to do a PFC test and that according to GN3 this test should be performed
at every relevant point of the installation
Am I just wrong about the tester giving the ZE and PFC at the same time? The tester in question was either a Megger 1552 or a Di-Log 9083p

WHen you say Ze for shower where did you take reading, ZE is taken at the supply with the installation isolated safely with the earthing conductor disconnected to remove parallel paths to earth and this is the ZE for the whole installation at origin ie incoming side of main isolator switch

FOR pfc this is also taken at supply side of main switch with the final circuits isolated
firstly make sure you have reconnected your earthing conductor to the met and isolated the load ie final circuits
then using megger 1552 test incoming side of main switch LINE and earth at the MET this is PEFC
then test between LINE and NEUTRAL at the incoming side of main switch this is PSCC the highest of these two values is the PFC which must be recorded on the certificate

as for at every relevent point
If the breaking capacity of all overcurrent protective devices ie CBs, fuses etc are greater than or at least equal to the PFC at origin then you dont need to test at at any other relevant point as pfc will always be higher at the origin

hopr this helps mate

 

[noidea]

Thanks BruceLee.
I am doing the ZE at the main supply with the main earth disconnected. Maybe I worded my question wrong. I know I said that I was measuring the ZE for the shower. What I meant is that, whilst doing all the relevant tests for every installation, ie, R1 R2 IR etc, ZE is one of those tests. What I was trying to get at is once I have done the ZE can I then use this result for all the other circuits I need to test rather than repeating the test again and again?

 

[brucelee]

Thanks BruceLee.
I am doing the ZE at the main supply with the main earth disconnected. Maybe I worded my question wrong. I know I said that I was measuring the ZE for the shower. What I meant is that, whilst doing all the relevant tests for every installation, ie, R1 R2 IR etc, ZE is one of those tests. What I was trying to get at is once I have done the ZE can I then use this result for all the other circuits I need to test rather than repeating the test again and again?

yeah mate ze at origin and only needs to be tested once and add this value to all your individual R1+ R2 values to give your ZS for each circuit and you only have to carry out a ZS test at sockets using plug in lead CAlculate the rest from Zs = ZE + (R1 + R2) calculating will always give higher reading as measuring Zs will include parallel earth paths ie Bonding to gas and water
when you have all your Zs make sure they are lower than 80% values of bs7671 max compare them to the values in GN3 or on site guide these are 80% values

 

[noidea]

Thanks again, one last thing.
Shoud the results for the PFC remain constant. For instance if my result was 0.75ka, would it be the same result or near enough every time I carried out the test or can it fluctuate for whatever reason?

 

[brucelee]

they will prob be different mate as it depends how far from supply transformer etc
for a TN - C - S the pefc and pscc will be the same as each other

for a three phase pfc will always be higher between the lines and as most testers you cant measure between the lines you measure all the line to neutrals and then multiply the highest by 2 this is the pfc

for Ze if you have a main distribution board supplying a remote ccu ie in a shed then the ZE for this second board is the ZE of the supply plus the R1 + R2 for the circuit ie swa to garage, shed etc then this is the ZE for the secondary board and is generally known as the Zdb and this is recorded on a second schedule of test results as the ZE for this board with the final circuits for this board

the ZS for this second board is then ZE at supply +( R1 + R2 ) ie swa +( R1 +R2) for the final circuits of this board