high pfc domestic property

[Deleted member 38070]

hi, fitted new consumer in a domestic house.

testing.

ze 0.16
zs at origin 0.04
pfc 6.2ka

the pfc is my problem, ohms law would make the pfc work out around 5.7Ka (using 0.04 as your resistance) (with all paths in place)
using megger 1553 two lead test, high current, pefc and pscc are the same as its pme

im starting to think my meter is faulty, cant think of any other reason for the reading...

i did read if its downstream from 100A bs1361 cutout then effectively if 16Ka breaking capacity, that doesnt really help with mcbs rated at 6Ka

what are your thoughts as ive drawn a blank...?

the pfc just seems too high, its a new (to me) meter, with calibration cert done in jan

thanks for any help

 

[spark 68]

In another thread on the same subject I pointed out that the OCPDs themselves can have significant impedances at the kA fault level (current limiting), as well as the relatively smaller size conductors on the outgoing ways, for instance what are the chances of say obtaining 16kA fault current levels at the outgoing way of a 6A breaker connected via a 1mm conductor ?, the further away from the origin you get the PFC rapidly diminishes. A small rise in impedance (both outgoing conductor and OCPD impedance) has a much larger corresponding effect on the PFC.

BS7671 even has a provision for this, as it does say this in parts further down in 435.1, "it may be assumed that the requirements of this section are satisfied as regards fault protection of the conductors on the load side of that point."

I read this (the bottom of paragraph of 435.1) to mean if there are doubts in respect of PFC levels that a further PFC measurement at the load side of that OCPD may well confirm that the OCPD is suitable, or not as the case may be., there are of course other exemptions, such as the 3m rule, annexe Za etc.

 

[Anthony S]

Also see page 62/63 GN3