Prospective Fault Current

[eckersecker]

I recently fitted a dual RCD MK board in a house. Everything has tested out fine but I was a bit concerned about the following readings. Ze is 0.03 ohms and the PFC is 7.3 KA. The supply transformer is just over the yard wall.
The breakers in the board are rated at the usual 6.0 KA. Do you have to change them?

 

[malcolmsanford]

No .................................. your DNO fuse will most likely be rated at 16.5 Ka and therefore ample.

Also what was the ZS for your circuits ? that will be the fault current on those individual breakers.

Finally remember most MFT are not designed to work at tolerances as low as you have there.

 

[Deleted member 26818]

Consumer Units, are a particular kind of DB, that are type tested, intended for use by ordinary persons, and rated at 16.5kA.
DNO cut out fuses are variously rated between 16kA and 80kA, depending on type, and voltage.