Lighting spur off a ring

[Newbyspark]

This is just a 'not sure' why question.

when spurring off a ring circuit for a small light circuit, why does it have to be fused down to 3 or 5 amp. Why can't you use 2.5mm cable instead as the mcb is protecting the cable. Is it because most switches are only designed for the lower ampage.

please don't jump down my throat, I always do it the correct way it's just a ponder.

 

[Plonker 3]

Not thinking straight here!!!!!!!!!!!!!!!!!!!!

 

[uksparks]

Well both reasons I'd say, the switchgear is only rated at 10A usually I think, plus if you used 1.5mm cable it cannot take as much current as the breaker on a normal 32A ring thus damaging the cable or over heating it etc should you overload the spur. And you theoretically could expose the fitting or switchgear to more than its rated at should you use a 10A switch to switch a light fitting and washer etc..

I suppose you argue to say you have designed it so that it's only one light on the spur and know it physically cannot draw any more but I guess that's not the point as some dosey person might then extend it further and stick a double socket and dishwasher on it.

If you fuse it down correctly, it will safely protect the cable, if you don't, take a double socket as a spur with a bit of 2.5mm, you could say you could plug extensions in that and draw up 26A, but 2.5mm one leg can only take 24A, anyway, my point is, fuse it down and you know it's protected even if it gets modified by a numty in the future.

 

[micknew]

This is just a 'not sure' why question.

when spurring off a ring circuit for a small light circuit, why does it have to be fused down to 3 or 5 amp. Why can't you use 2.5mm cable instead as the mcb is protecting the cable. Is it because most switches are only designed for the lower ampage.

please don't jump down my throat, I always do it the correct way it's just a ponder.

DIY question.

 

[Lucien Nunes]

Most lighting fixtures including BC and ES lampholders are designed to be protected at a maximum of 16A. Connecting an ordinary lampholder to an RFC protected at 32A would therefore be unacceptable. However, it might be compliant (although not necessarily recommended) to fuse the lighting spur at 13A.

 

[uksparks]

Most lighting fixtures including BC and ES lampholders are designed to be protected at a maximum of 16A. Connecting an ordinary lampholder to an RFC protected at 32A would therefore be unacceptable. However, it might be compliant (although not necessarily recommended) to fuse the lighting spur at 13A.

I thought most were 10A? I know MK light switches are sold as 10A 2 way etc...

 

[Newbyspark]

DIY question.

Not DIY thanks micknew, just a question.

 

[spark 68]

I thought most were 10A? I know MK light switches are sold as 10A 2 way etc...

Yes but that is for the load it is actually switching, you would need a fair amount of lights on that switch to exceed 10A, where that genuinely is the case (commercial/industrial) you tend to find the switch controls a contactor.

 

[uksparks]

Yes but that is for the load it is actually switching, you would need a fair amount of lights on that switch to exceed 10A, where that genuinely is the case (commercial/industrial) you tend to find the switch controls a contactor.

Quite true, the beauty of contactors, you can literally switch anything!

 

[RyanCheetham]

Not to mention trying to 3plate 2.5mms in a fancy light fitting

 

[uksparks]

Not to mention trying to 3plate 2.5mms in a fancy light fitting

Yes, that would be a pig of a job indeed!

 

[MDJ]

This is just a 'not sure' why question.

when spurring off a ring circuit for a small light circuit, why does it have to be fused down to 3 or 5 amp. Why can't you use 2.5mm cable instead as the mcb is protecting the cable. Is it because most switches are only designed for the lower ampage.

please don't jump down my throat, I always do it the correct way it's just a ponder.

would never consider it unless in a shed fed from a spur unit off the ring
okay in commercial lighting but a right pita in a domestic ceiling rose

anything else?

 

[Guest111]

Saw one on a house renovation programme the other day,2 wall lights mounted above twin sockets and a lovely line of new plaster between the 2,not an fcu in sight

 

[Geoffsd]

Appendix 15 is neither mandatory nor exhaustive - see notes under the heading and 433.3.1(ii).