PSC/PFC the difference

[user 2912]

Can anyone tell me the difference between PSC and PFC and why the difference is important....

 

[Barx]

PSC = Prospective Short-circuit current = Live-Neutral short

PFC = Prospective Fault Current = Live-Earth Short

PFC is the one that tests the earth path.

 

[user 2912]

So I take it that the PSC will be higher than the PFC, so you need to test both so you can not only be satisfied that you acheive your disconnection times but also that you protective device will withstand a direct short.

 

[Andy™]

So I take it that the PSC will be higher than the PFC, so you need to test both so you can not only be satisfied that you acheive your disconnection times but also that you protective device will withstand a direct short.

in TT and TN-S, L-N will be higher. in TNC-S, L-N should be the same as L-E

You need to check both to make sure that the breakers are rated to break the worst case load. in domestic, this isnt normally a problem, but in commercial/some domestic you may need 10KA breakers instead of 6KA

And welcome to the madhouse

 

[mikel]

AFAIK on a single phase either could be bigger, it depends on the resistance of the circuits return paths. You need to measure both to determine which is the highest

 

[M107]

Measure both & highest goes on the cert.

 

[user 2912]

so would you use the PFC to check your disconnection time as it will be lower so you get the worst case scenario and the PSC for your fuse ratings.

 

[Andy™]

Also remember L-L will be higher that L-N and L-E on 3 phase

 

[Andy™]

so would you use the PFC to check your disconnection time as it will be lower so you get the worst case scenario and the PSC for your fuse ratings.

you check Zs against charts to make sure there is enough fault current to open breaker

 

[green-hornet]

Measure both & highest goes on the cert.

This is the right answer

 

[septiclecky]

Also remember L-L will be higher that L-N and L-E on 3 phase

Also as L-L is higher but some meters can only measure on single phase, you double the maximum reading for 3 phase.