help needed with PEFC and PSCC!!

[cmacca81]

Hi, i understand how to test for PEFC and PSCC, and that the highest reading is recorded. It might be a silly question, but i don't understand the reason i am testing for it. The maximum breaking capacity of say, a 16amp type b circuit breaker is 6000amps and i get a reading for pscc of 0.45ka. Does this mean it will be ok as its a lower reading than 6000amps? is it that the lowest possible reading achieved, is safer? really confused here!! any help will be much appreciated!!

Thanks

 

[a1]

It is to check that the Protective device is capable (large enough) of clearing the fault.

 

[kme]

Does this mean it will be ok as its a lower reading than 6000amps? is it that the lowest possible reading achieved, is safer? really confused here!! any help will be much appreciated!!Thanks

Yes, it would be okay - 450A<6000A.

The higher the reading, the better (generally), as the protective device will trip quicker. If you`re very near a substation, esp. in a town centre, you COULD get readings in excess of 16KA. Then you have to ensure you have a protective device / devices which are cabaple of breaking such a current safely.

HTH

KME

 

[Brian 157]

If your MCB is capable of handling 6kA but your PSCC/PEFC is above this value there is a chance that the MCB could be damaged by the fault current and may not work correctly afterwards, causing a potentialy dangerous installation.

 

[m4tty]

Is this situation not ok if the main fuse is capable of breaking the fault current??

 

[kme]

If your MCB is capable of handling 6kA but your PSCC/PEFC is above this value there is a chance that the MCB could be damaged by the fault current and may not work correctly afterwards, causing a potentialy dangerous installation.

Partially, but see below.

Is this situation not ok if the main fuse is capable of breaking the fault current??

To a point. However, along the lines of Brian`s post above, a large differential can have issues. If an item rated for a PSCC of 6KA were to attempt to open a fault current of more than that, there is an explosion risk, with attendant plasma flash. bad day explode

In most cases, even if the breakers themselves are not rated capable, breakers in most consumer units and dist boards are covered to 16KA.

HTH

KME