readings?

[SIIVION]

Good day.
I have recently been involved in an EICR on a property with 15 DB's.

The average PFC appears as 90A and the average Ze is 2.9
The system is TN-S

I suspect there is an earth fault somewhere which would explain the Ze but why the PFC reading?

Each DB is isolated by a BS88 80A or 100A at distances ranging from 5m to 30m

Any ideas?

 

[telectrix]

are you talking a bout Ze ( at the origin) or Zdb at each board? pefc will be possibly higher than expected due to parallel paths.

 

[ipf]

Not too much in it, though...if you divide 240 by 90....

 

[davesparks]

Average Ze and PFC?

What values are you calculating this average from?

 

[Andy78]

Average Ze ? are you on about Zdb ? Your PEFC sounds about right for an EFLI of 2.9 ohms. You can work it out with sums and that. Talking of sums, do your Zdb readings match with what you calculated from your continuity readings of the sub feeds ?

 

[ipf]

Average Ze and PFC?

What values are you calculating this average from?

I was wondering that! Only one Ze how do you get an average?

 

[SIIVION]

sorry not enough information for you...
The average was taken from the readings of all 15 boards.
Also, yes you are right all Ze should be Zdb.
Range of PEFC is from 88 to 90.
Zdb range is 2.8 to 3.0

Thank you for your information, I should have thought about it a bit more rather than just jumping straight on here. So used to getting far lower Ze and much high PFC on single board tests.

 

[davesparks]

Why are you calculating an average Zdb and PFC from multiple boards ?
What did you hope to get from doing this?

What is the Ze of the installation?

 

[SIIVION]

Average Ze ? are you on about Zdb ? Your PEFC sounds about right for an EFLI of 2.9 ohms. You can work it out with sums and that. Talking of sums, do your Zdb readings match with what you calculated from your continuity readings of the sub feeds ?

Thankyou. All the Zdb values do seem very high. As an example one Zdb reading is 2.7 where the calculation for a 30m run of 10mm 2 core SWA (using armour as earth) is 0.2 .

 

[telectrix]

but you've not yet told us the Ze at source. it could be a DNO problem.

 

[davesparks]

Thankyou. All the Zdb values do seem very high. As an example one Zdb reading is 2.7 where the calculation for a 30m run of 10mm 2 core SWA (using armour as earth) is 0.2 .

Something is a bit wrong then methinks.

 

[Andy78]

Agree with the above comments.... a measured Ze for this install is needed.

 

[SIIVION]

Why are you calculating an average Zdb and PFC from multiple boards ?
What did you hope to get from doing this?

What is the Ze of the installation?

I am only giving the average to save listing all the readings.
I will find out the installation Ze tomorrow, it has not been physically possible for me to measure.

 

[davesparks]

I am only giving the average to save listing all the readings.
I will find out the installation Ze tomorrow, it has not been physically possible for me to measure.

How did you come up with the predicted Zdb in post 9 without a Ze to make that prediction with?
Do you have a Zdb at the intake position?

 

[Engineer54]

Thankyou. All the Zdb values do seem very high. As an example one Zdb reading is 2.7 where the calculation for a 30m run of 10mm 2 core SWA (using armour as earth) is 0.2 .

I hope there isn't any main bonding conductors being taken to this and the any other DB's that are being supplied with 2 core SWA cables, as the armouring will not have a sufficient CSA for compliance??

Apart from that, something is very wrong here with the values you are stating for the Zdb's of these DB's....