L-E fault always trips mcb?

[caterhamboy]

Hi, i am studying my 3rd yr 2330 and soon to do my fault finding, and was wondering if you had a L-E fault if the mcb would always trip or if just the rcd would trip sometimes on a 17th edition board?

 

[Marvo]

Depends on the resistance of the fault path.

 

[Deleted member 26818]

As above.

 

[clematis432]

If the fault is of a very low impedance (which most earth faults are) the mcb will trip. But as Marvo says if the impedance of the earth fault path is high the mcb may not trip.