Need SIMPLE explanation of PFC

[cleeve]

I had a new installation at home certified recently and was told to tell the electricity supplier that [in the "Supply Characteristics & Earthing" section] the Prospective Fault Current (PFC) was very high at 84kA. Before contacting EDF and have them tell me that it's my fault I would like to understand what I'm talking to them about.
I've read everything I can find in respect of PFC but still don't understand just what it means. Or what a typical value should be. Or what causes it. Or what I should expect them to do about it.
Other posts i.r.o. PFC all seem to quote a Ze value so, if it's relevant and to save anyone asking, in my case it is 0.28 Ohms. I don't know where the substation is, but apparently it is "not particularly close".
If you can give an idiots guide to PFC and answer the above concerns I'd really appreciate the help.

 

[ChrisRogers]

84ka? Please double check as that figure isn't possible on a standard tx.

 

[jamesmcbride]

If your ze is .28, your pfc should be around .8kA. It could be a little bit higher than that, but not to that degree.

Do you know what type of supply you have?

I would say it was recorded incorrectly.

The PFC is calculated (usually by the test equipment) by measuring the impedance of the loop back to the supply transformer between line and neutral and line and earth and dividing each by the supply voltage. assuming you have a single phase supply, the highest of these will be recorded as PFC

 

[viewer]

Decimal point has slipped - should be 841A - not 84000

 

[EFLImpudence]

Was it the same person who measured the Ze who told you the PFC was too high?

 

[Spark123]

PFC might be L-N, (or L-L in the case of 3 phase) just depends on the supply.
But 84kA - either he has his own supply transformer, the tester is goosed or it has been misread!

 

[cleeve]

Thanks everyone for the input.
Maybe the test equipment was on the wrong scale or a simple mis-reading. I'm going to believe the suggestions that it should have been .836kA as that seems much more in-line with what I have read.
I'll get back to the contractor for an explanation or new certificate instead of battling with EDF.

 

[kai]

8.4.kA or Eight and a half thousand amps is a more reasonable PFC figure on a standard 100amp supply, remember modern breakers are often designed to safely cope with around 10 kA Ten thousand amps max fault current.

A UK standard domestic 100amp single phase supply has a max 16.5.kA PFC.

It looks like the decimal point was out quite a bit.

 

[jamesmcbride]

8.4.kA or Eight and a half thousand amps is a more reasonable PFC figure on a standard 100amp supply, remember modern breakers are often designed to safely cope with around 10 kA Ten thousand amps max fault current.

A UK standard domestic 100amp single phase supply has a max 16.5.kA PFC.

It looks like the decimal point was out quite a bit.

Really? With that Ze?

Obviously it will depend upon the supply type, but surely if It was TN-C-S or TN-S, the PEFC and PSSC would be fairly similar and certainly not out to the degree of 10 times?

 

[ricicle]

I would have struggled to see 84kA stood next to one of our factory transformers !
Most testers can't get accurate readings when close to a supply transformer anyway, and you wouldn't in a million years get that sort of reading once you start adding cable impedance and move away from the Tx.