low PFC

[beats]

evening
I've just doing some domestic periodic inspections today and 2 of my properties gave me low PFC readings of 0.52pfc, 0.40 Ze and 0.47pfc and 0.44 Ze both systems were TNS. Are these considered as a low reading as they are to what i would normally expect? and is the a lower limit to PFC?
ta

 

[telectrix]

looks about right. TN-S Ze can be up to 0.8 ohms which would give a pefc of 287A. so your readings are fine. on your PIR you should recdord PSSC ( Line/Neutral ) as it will be the higher value.

 

[beats]

Thanks for the quick reply.
thats good then.i knew the ze was ok,just the pfc was lower than i normally get.Just thought i'd check before i print the certs off.

 

[Trulyshocking]

looks about right. TN-S Ze can be up to 0.8 ohms which would give a pefc of 287A. so your readings are fine. on your PIR you should recdord PSSC ( Line/Neutral ) as it will be the higher value.

Just as a matter of interest (I work industrial and not domestic), how do you know the PSCC will be higher than the PEFC?

 

[Jay Sparks]

Just as a matter of interest (I work industrial and not domestic), how do you know the PSCC will be higher than the PEFC?

Because PSCC is between the line and neutral and the csa of these cables will be the same size but the PEFC is between line and earth and the csa of the earth is normally smaller than the line, so more resistance, this meens the pfc will be higher on the PSCC.

 

[Trulyshocking]

Because PSCC is between the line and neutral and the csa of these cables will be the same size but the PEFC is between line and earth and the csa of the earth is normally smaller than the line, so more resistance, this meens the pfc will be higher on the PSCC.

Interesting.... I normally see a higher PEFC which is why I asked..... but then I work on a private network so It's different. I always imagined that domestic supplies in towns would have incredibly low Ze's!!

 

[Jay Sparks]

Interesting.... I normally see a higher PEFC which is why I asked..... but then I work on a private network so It's different. I always imagined that domestic supplies in towns would have incredibly low Ze's!!

I used to find that the pfc was incredibly high when the house was close to the sub station. I once had a reading of 7.2ka which was higher than the 3ka rcbo's installed in the cu. When I phoned the boss he said it was ok because the main cut out was 16.5ka.

Jay

 

[Trulyshocking]

I used to find that the pfc was incredibly high when the house was close to the sub station. I once had a reading of 7.2ka which was higher than the 3ka rcbo's installed in the cu. When I phoned the boss he said it was ok because the main cut out was 16.5ka.

Jay

I quite often see 20KA (On 3 Phase boards after I've doubled the PSCC ) which is a bit unnerving but like you say, the upstream protection is generally a BS88 @ 80KA so it's OK!! Wouldn't want to be working in the live DB tho!!