Pfc and pscc

[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