You cannot post a reply to this discussion. If you have a question start a new discussion
Needing to meet mcb zs with ln loop.
Former Community Member
Where an rcd is relied on for fault protection due to high zs it has been suggested to me that the loop between live Conductors needs to be less than the mcb max zs. I can't find anything on this anywhere but he said he had this confirmed by an niceic assessor. Have I got it wrong ?
The RCD is only providing the ADS for earth faults - it won't "see" a short circuit fault
If the L-N loop is so long, then you also have potentially limited or no short circuit protection
The MCB "Zs" is simply a means of stating what the minimum earth fault and short circuit current needs to be for a stated time
Take note however, that for short circuits, there is no "minimum time" other than that dictated by the cable not bursting into flames - an adiabatic check essentially
The RCD is only providing the ADS for earth faults - it won't "see" a short circuit fault
If the L-N loop is so long, then you also have potentially limited or no short circuit protection
The MCB "Zs" is simply a means of stating what the minimum earth fault and short circuit current needs to be for a stated time
Take note however, that for short circuits, there is no "minimum time" other than that dictated by the cable not bursting into flames - an adiabatic check essentially
