Pfc and pscc

[vbyrne]

Could anyone out there give me a detail explanation on what is the above test reading proving, is it that you have for a very low reading good continuity through the connections at the equipment at the origin of a installation. And what makes the reading vary from one installation to another.

 

[Geordie Spark]

https://www.youtube.com/watch?v=5vnyXGHvqzU

 

[Leesparkykent]

prospective short circuit current is the highest current that can exist in an electrical system under short circuit conditions, it is determined by the voltage and impedance of the supply so PSCC= voltage/Ze

 

[trev]

prospective short circuit current is the highest current that can exist in an electrical system under short circuit conditions, it is determined by the voltage and impedance of the supply so PSCC= voltage/Ze

Not necessarily, in a TN-C-S PEFC and PSCC will be the same (give or take) but in other earthing systems they are not going to be the same so the calculation you post isn't always going to apply.

 

[Leesparkykent]

Not necessarily, in a TN-C-S PEFC and PSCC will be the same (give or take) but in other earthing systems they are not going to be the same so the calculation you post isn't always going to apply.

cool, every day is a school day

 

[Leesparkykent]

is pfc measured phase to earth and pscc phase to neutral?

 

[trev]

As far as I remember, through a slightly drunken haze, Lee the calc you posted relates to PEFC only although I do stand to be corrected on that. As I say, I'm half cut just now.
That's why both PEFC and PSCC are measured, one of the many things the test is useful for is making sure the MCBs aren't going to explode into a million different pieces when the fault current happens, or to put it another way, that they have sufficient breaking capacity.
It also proves that you have a viable earth and that the impedance of the earth fault loop is withing specified parameters

 

[trev]

is pfc measured phase to earth and pscc phase to neutral?

pEfc is measured between live, neutral and earth conductors because it is measuring the prospective earth fault current. IE that fault current that will flow between live conductor(s) and earth.
Whereas prospective short circuit current is measuring that which will flow if a short occurs between live conductors IE live and neutral.
The higher of the two readings is referred to as the Prospective Fault Current (pfc) for the installation. If you're sitting a testing exam you have to make sure you get the terminology right mate.
Make a mess of your terminology and you are going to drop points.

 

[trev]

You might think I'm being needlessly pedantic Lee but I get the feeling you're a trainee so it has to be drummed in that you have to get the terminology right. This isn't like school mate, C&G examiners will not give you the mark because they know what you mean.

 

[davesparks]

PSCC is measured between all live conductors, so that's from line to neutral and line to line in a 3 phase supply.

 

[trev]

PSCC is measured between all live conductors, so that's from line to neutral and line to line in a 3 phase supply.

Was trying to keep things simple mate

 

[Leesparkykent]

You might think I'm being needlessly pedantic Lee but I get the feeling you're a trainee so it has to be drummed in that you have to get the terminology right. This isn't like school mate, C&G examiners will not give you the mark because they know what you mean.

no not a trainee, but must admit some times my terminology isn't up to scratch so to speak, I am graded as approved on my jib card lol

 

[trev]

I apologise unreservedly then
The last sentence still applies though mate

 

[Rockingit]

Peeps seem so quick to forget Mr Zl.....

 

[guest119]

Peeps seem so quick to forget Mr Zl.....

I remember Mr Zebidee.

 

[HandySparks]

Peeps seem so quick to forget Mr Zl.....

Indeed. I will usually do a line impedance check at the same time as I do a Zs. It's a quick way of checking the integrity of the neutral path. I think it's odd that it's not used more.

OK, maybe it's not such a dangerous situation as a line to earth fault, but in the event of a line to neutral short, it's the line impedance that determines the disconnection time.

 

[guest119]

OK, maybe it's not such a dangerous situation as a line to earth fault, but


You are of course talking of sp & n installs?

 

[davesparks]

Indeed. I will usually do a line impedance check at the same time as I do a Zs. It's a quick way of checking the integrity of the neutral path. I think it's odd that it's not used more.

OK, maybe it's not such a dangerous situation as a line to earth fault, but in the event of a line to neutral short, it's the line impedance that determines the disconnection time.

But if the line impedance is high then it will be noticed very quickly as it will affect the normal operation of the installation.

 

[stevethesparks]

It may not just be the neutral path but by poor design live and neutral, whereas a satisfactory Zs reading may be obtained by parallel paths.
I also think it a good idea to conduct a Line impedance test, particularly where Zs readings are close to their limits.

 

[HandySparks]

But if the line impedance is high then it will be noticed very quickly as it will affect the normal operation of the installation.

Indeed, although dependent on how heavily it's loaded and the type of load. If it's just a heater, poor line impedance won't be noticed as quickly as, say, lighting.

 

[SirKit Breaker]

PFC is the generic terminology used for Prospective fault current, whether it is PEFC or PSCC.

It then breaks down as thus

PEFC. Prospective Earth Fault Current. A fault between a LIVE conductor and EARTH. A LIVE conductor can be a LINE or NEUTRAL conductor.

PSCC. Prospective Short Circuit Current. A fault between LIVE conductors. The highest current will flow in a fault between all 3 LINE conductors.

Although some test instruments can test between LIVE conductors, it is generally not acceptable as safe practice, so you would test between each LINE conductor and EARTH, and take the highest test result and double it as this errs on the side of caution, and record this value as your PFC result.

If your tester can't do a LINE to LINE test, and you try it, you may well end up with bits of plastic in your face or worse, and you wont be laughing about it in the pub, your local A&E wont think you are funny either, but the local undertaker may be thankful for your business.

Hope that clears things up a bit, and as said by someone else, the terminology is very important.

Cheers..............Howard