Lighting circuit supplied from a 32A ring main socket.

[Cashman]

Hi guys, I am adding a lighting circuit to a Ring main 32 A. Can I just use a 6A MCB type B in a box on DIN rail to supply my lighting. I am using 1.5mm cable after the 6 A MCB.
Thanks for your advice!

 

[M-Ty]

It depends on whether the ring circuit is supplied through an RCD.

 

[Lister1987]

From ring to an FCU, onward to the light fitting, add in switch drop and fuse with 5A, tend to see it a lot in garages

 

[pc1966]

As above, a FCU with a 5A fuse is the simplest option, just added as if it were a socket on the ring.

Or even as a spur. Though personally I dislike spurs due to the options for abuse (adding more later and not limited to 13A) as well as the higher risk of a conductor not being properly clamped if there are 3 (or more!) in an existing socket.

 

[Cashman]

It depends on whether the ring circuit is supplied through an RCD.

Yes, it does

 

[Cashman]

My issue is though in terms of short circuit by the lght, both the 6A mcb and the 32A mcb trigger. I would rther the lighting mcb to trigger only. shall I change into a rcbo o a different cb?

 

[Pete999]

My issue is though in terms of short circuit by the lght, both the 6A mcb and the 32A mcb trigger. I would rther the lighting mcb to trigger only. shall I change into a rcbo o a different cb?

Feed the lighting through a FCU with a 5Amp cart fuse and, forget the 6A breaker and enclosure,

 

[Cashman]

Feed the lighting through a FCU with a 5Amp cart fuse and, forget the 6A breaker and enclosure,

good alternative!

 

[Pete999]

good alternative!t.The only safe alternative I think.

 

[Cashman]

well , the 6 AMP mcb type B is overload and short circit protecting the lighting circuit. Only issue was to avoiding the 32 AMP ring mcb to trigger, hence the alternative CB . It needs calculating the arc current etc to determine the right mcb, but honestly I cannot bother as long as circuits are correctly sized.

 

[pc1966]

You won't get much selectivity between MCBs. Check the manufacturer's tables for selectivity, or for Schneider this tool works (but only on Chrome web browser, it seems, which is crap):
https://hto.power.schneider-electri...f9fa18492b&client_id=cbt#/CheckDescrimination

Hager for the NBN series give 0.45kA limit (i.e. if your fault Zs is below 0.51 ohms then both fire).

Having said that, you won't get much selectivity with MCB - fuse either, though the Schneider tool seems a bit broken for that but from the current-time plots you are looking at 0.1kA limit (i.e. lower magnetic trip threshold of 3 * 32A for B-curve MCB)

 

[Lister1987]

good alternative!

I called it first ??