High PFC

[66ryanj]

Have just finished Re-wiring a flat in a built up area near town centre. Began testing today and tested the PFC to be 7.49KA..... and the ZE to be 0.03.

I have allready installed tybe B 6KA breakers assuming the PFC would be ok.

Has anyone come across a similar situation? and what did you do?

Thanks. Ryan.

 

[cadspark]

If the main incomer is BS88 you are covered by that up to 16.5 Ka and BS1361 II for upto 33 Ka.

 

[sparkytim]

+1

Have had similar due to being very near to Sub station Transformer

As said above Back up protection is provided by the Service fuse IF it is BS 88 or 1361, and your Consumer Unit meets BS EN 60439 Part 3,

 

[66ryanj]

The service fuse is a bs 1361. does this mean I do not have to upgrade my MCBs to10KA

 

[Sidewinder]

^ concurr!

Not perfect, but much more than acceptable, as long as the CU complies, which it should ,something in annexe ZA IIRC, anyone?

 

[sparkytim]

Correct

Annex ZA of corrigendum June 2006 to BS EN 60439 1991 Part 3

 

[Doc Hudson]

Just out of curiosity wouldn't you normal have checked the PFC, PCCS, Ze and or Ra before commencing work so you can be sure of the incoming supply before making changes?

Doc H.

 

[septiclecky]

The service fuse is a bs 1361. does this mean I do not have to upgrade my MCBs to10KA

You will need to up grade your MCBs as even though your main incomer protection is rated at 16.5kA with such a low Ze and a low R1+R2 there will be a potentional for a fault current greater that 6kA but less than 16.5kA.

If the main fuse does not blow and your MCBs do trip due to this fault current flowing through the MCBs then under manufacturers info they should be changed.

 

[Sidewinder]

septic,

Even though this situation is not perfect, it is, believe it or not, acceptable as it is OK to rely on the DNO fuse in this situation, in domestic premises!

 

[kme]

Agreed. The "ZA" annexe affords the "whole consumer unit" a 16KA rating, irrespective of the individual breakers (subject to certain conditions). Once the MCBs are within the enclosure; the 6KA rating, whilst still noted, can be ignored.

KME