PFC reading of 8ka on domestic installation

[matt1973]

Hello , ive just got off the phone to niceic regarding a pfc reading of 8ka.

Ze reading of 30.2 ohms on a tt installation and pfc of 8ka.

MCBs rated at 6ka so obviously I was not happy with the higher test result. Niceic said all was ok due to 230 divided by 30.2 = fault current of 7.6A and all circuits are rcd protected. does anyone think I have read my test results wrong? or am I barking up the wrong tree here.

any advice would be appreciated for this new member.

 

[SparkyChick]

The 7.6A seems about right for PEFC, but what's PSCC?

Welcome to the forums btw

 

[suffolkspark]

8A would seem roughly inline with the calc so i rekon your reading your meter wrong

 

[matt1973]

Hi sparkychick, thanks for the welcome.
just got home, left results on site, I will confirm next week when I return to finish on Tuesday.

 

[Ian1981]

Yes but remember the live to neutral pfc will be the higher 99% of the time on a TT installation so this will be recorded on the certificate.
You are allowed to have coordination between OCPD’s upstream of your mcbs ie back up protection as long as the manufacturers data allows Regarding the let through energy of device
Regulation 434.5.1

 

[matt1973]

that was my thinking contact, never done so before but always a first time I guess

 

[Sintra]

The 7.6A seems about right for PEFC, but what's PSCC?

Welcome to the forums btw

Prospective short circuit current.

 

[marconi]

pfc= 8000A?

 

[matt1973]

Prospective short circuit current.

took me a while to get that

 

[Gavin John Hyde]

By chance I am reading through GN3 this evening on the relevant sections.
How does this tie in to GN3 on page 72 of the 18th ed version)( havent got 17th to hand)although it says same thing.
Fault Currents upto 16kA
" the short circuit capacity of over current protective devices incorporated within consumer units may be taken to be 16 kA where
(a) the consumer unit complies with BS EN:61439-3:2012
(b) the consumer unit is supplied through a type ii fuse to BS 1361:1971 rated at not more than 100 A on a single phase supply with a nominal voltage up to 250V"
Can we not then if the above are met treat the 6kA short circuit capacity as 16kA instead?

 

[Strima]

Hello , ive just got off the phone to niceic regarding a pfc reading of 8ka.

Ze reading of 30.2 ohms on a tt installation and pfc of 8ka.

MCBs rated at 6ka so obviously I was not happy with the higher test result. Niceic said all was ok due to 230 divided by 30.2 = fault current of 7.6A and all circuits are rcd protected. does anyone think I have read my test results wrong? or am I barking up the wrong tree here.

any advice would be appreciated for this new member.

So the technical helpline doesnt know the difference between PEFC & PSSC? That’s concerning....

 

[johnduffell]

It's ok with a proper consumer unit backed up by a cutout fuse. The cutout fuse protects the MCB as it would also blow in the case of a short circuit outgoing the mcb. Ie no discrimination at high currents.
Also the measured pscc can often end up higher than what would actually flow in these extreme situations.
Is the transformer on the other side of the wall? If not, the reading would be suspect.

 

[Strima]

@jdtae why the dumb rating then?

 

[Silly Sausage]

@jdtae why the dumb rating then?

I'd put it down to a certain helpline