PFC and circuit breakers

[Ken77]

Hi,

I was wondering if anyone could provide any advice on following:

I have PFC reading of 9.6 KA and was wondering what the ruling was for short circuit capacity for individual breakers. There are four circuits in total on the board, each currently with 6KA limit. Should these be changed to 10KA, or as PFC is spread across the whole installation is this ok?

Thanks

 

[Guest55]

if the pfc reading at the CU / Dis Board is 9.6 ka then yes , mcbs should be rated for 10.

 

[Risteard]

Unless it is covered by the 16kA conditional rating...

 

[Sintra]

What is the kA rating of the device upstream supplying the cu. If this is greater than 9.6 Ka then the 6 kA MCB's can remain.

 

[Guest55]

whats wrong with putting in the correctly rated devices ?

 

[scotsparky]

10ka is normal now so easy swap. i would just go for it. If the PFC was over 10KA then i would consider the installation of upstream devices that could cover it.

 

[Sintra]

Nothing but what's wrong with leaving ones that don't need changed.

 

[Guest55]

10ka is normal now so easy swap. i would just go for it. If the PFC was over 10KA then i would consider the installation of upstream devices that could cover it.

exactly , i like to know that the devices fitted can survive clearing a big fault current near the origin and still remain usable.
theres no guarantees of that if your relying on the higher pfc rating of the upstream device , simple good design if you ask me.

 

[Ken77]

I think I get it - so as at the supply it rated at 16KA the system is protected, even with a PFC of 9.6KA, so I can leave circuit breakers rated at 6KA as is.

 

[Sintra]

Yes you can. If you were installing a new cu for eg. then you would install 10kA rated breakers.