Can you explain this for me?

[twm.bwen]

Just looking through some old posts and it mentioned that if a 2.5mm t&e ring on a 32a mcb is broken its not good. To quote BAS 'not acceptable'.

Now, I understand a broken ring becomes two radials, so we have two ciruits served by one mcb, but the post says the 32a mcb is too large.
Is this because a socket on a ring draws some curent from each side of it so each side only has to take 16a before the mcb trips? And when it becomes two radials each side has t take a full 32a before tripping the mcn there fore loading the cable too much.



Is the gist of my theory on target or way off?

 

[tim west]

when joined in a ring the cable can carry more current than as radials the 2.5mm sq effectively becomes 4mm sq, when radials, the cable rating is less than the protective device rating so the breaker doesn't protect against overload as it did before and needs to be reduced accordingly.

 

[briwire]

Just looking through some old posts and it mentioned that if a 2.5mm t&e ring on a 32a mcb is broken its not good. To quote BAS 'not acceptable'.

Now, I understand a broken ring becomes two radials, so we have two ciruits served by one mcb, but the post says the 32a mcb is too large.
Is this because a socket on a ring draws some curent from each side of it so each side only has to take 16a before the mcb trips? And when it becomes two radials each side has t take a full 32a before tripping the mcn there fore loading the cable too much.



Is the gist of my theory on target or way off?

Thats spot on.