High PFC

[gtownspark]

Today I have been doing a PIR on a builderS merchants. The main 3phase DB is an old Melin Gerin board and the installation has a Ze of 0.06 with a PFC (PSCC) of 4.9x2=9.8KA. The MCB's within the board are rated between 3-6KA however the service fuses are 100A 1361/2 rated to 33KA

Does the board need upgarding with MCB's rated higher than 9.8KA or is the does the rating of the main services fuses provide the protection required?

Any advice in this respect greatly appreciated

 

[Dunc]

I've been told before that it doesn't as the main fuse is capable of handling the fault current without being damaged in the event that an MCB fails. I'm afraid I can't point you to a reg at this moment in time but in my opinion I think this seems all wrong as in the event of an MCB failing you could lose a whole phase.

 

[telectrix]

the psc flowing through the MCB's will be lower due to circuit resistance. i may be incorrect here, but it is my belief that it's only the service fuse/s that have to withstand the pssc at origin.

 

[roukel01]

agreed as above, providing the cutout fuse can cope it's ok.

 

[Chr!s]

Today I have been doing a PIR on a builderS merchants. The main 3phase DB is an old Melin Gerin board and the installation has a Ze of 0.06 with a PFC (PSCC) of 4.9x2=9.8KA. The MCB's within the board are rated between 3-6KA however the service fuses are 100A 1361/2 rated to 33KA

Does the board need upgarding with MCB's rated higher than 9.8KA or is the does the rating of the main services fuses provide the protection required?

Any advice in this respect greatly appreciated

Possibly, it depends upon the standard of the board and whether it falls within the scope of UK Annex ZA.

Some of the MCB'S may not receive any back up protection from the BS 1361 fuse.

Chris

 

[Deleted member 26818]

It's not a Consumer Unit, so it is not type tested and I doubt it would fall within the scope of UK Annex ZA.
The instantaneous operatioon rating of a 100A BS 1361 fuse, is over 7kA, as such I would would recommend upgrading the the MCBs to 10kA.

 

[Chr!s]

Cenelec Annex Za reffers

2.1.11 Customer distribution board

An integrated assembly, for the control and distribution of electrical energy, principally in a
household or similar premise, incorporating manual means of double-pole isolation on the
incoming circuit(s), with polarity observed throughout. They are designed for use exclusively
with specific protective devices on the outgoing circuits, and type-tested for use when energized
through the specified 100 amp fuse.

I agree with you spin, the likely hood will be MCB'S with a higher breaking capacity, though i would speak to the manufactures to see if they allow the set up in this instance.
Chris