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Posted By Topic: K rating of MCBs

Small
Mar 29 2018 19:52

How do you work out if you require 6 or ten k rated MCBs, have ajob that requires 3Phase 60amp board with meters, for a comerical workshop, not sure if 6k is ok, also do manufactures rate there boards k wise.
Cheers
   

pluto
Mar 29 2018 20:09

The kA value at the input to a protective device is solely covered by the size of the supply transformer prospective short current value and the impedance of the connecting cables from the transfomer to the input of the protective device.

The kA value of the protective must be able to safely interrupt the prospective short current.

Often the kA level can be neasured by some EFLI testers and then select the protective device.

On a new installation it must be calculated, as you are not able to measure the actual kA level. The kA calulations are not easy to do correctly and you may need to get professional help to do the calulations. The scope of your comments would indicate that you will need help to assist in the correct kA selection of protective devices.

For HRC fuses the kA rating will be typically 80 kA but the actual valuie will be marked on the fuse link.
   

AlecK
Mar 30 2018 12:19

The network should be both able and willing to tell you the PSSC at point of supply, and you can then take it from there.