spurs

[telectrix]

just been to look at a CU upgrade ( it's got a 16th board, 1 RCD for all ). on checking, found a couple of spurs off ring with 3 sockets on 1, and 2 sockets off other. not practical to ring these, or fit FCUs as recent expensive decoration been done. on checking the load situation on the ring, ( it's barely 12A with everything on ) i think , if i downrate the MCB to 16A, the circuit would comply. any thoughts appreciated.

 

[davelerave]

dunno what the UK rules are on de-rating rings and FCU's feeding multiple socket outlets

can you split the rings into radials rather than de-rate them

you wouldn't want to cause tripping on overcurrent on kitchens etc. anyhow if you derated them

 

[telectrix]

kitchen ring not the issue. its the downstairs living rooms. highest load is the PC with it's associated bits

 

[malcolmsanford]

There is nothing stopping you wanting to fit a smaller protection device to the ring, though appendix 15 does clearly state what a ring final circuit is and denotes the protection as being 30 or 32 amps. So you would mark that on your EIC as a departure from the Regs and as your fitting a smaller protection device on a rated cable your not going to make the installation less safe and should be ok. Reg 120.3

Though if it was me you have no need to do anything really. As your fitting a new CU then all you need to do is make your work in line with the 7671. Again on your EIC you note in the part comments on existing installation the spurs and advise the client that they do not come up to the Regs and you advise them to have them upgraded.

 

[spud1]

I suppose if you down rate you would stop excessive load being drawn on those spurs but only by making the protective device operate. If only 12A on full demand id consider likely changes in that demand situation and make conclusion based on it. I think if sockets serve a kitchen/laundry you ll have to rethink.

 

[telectrix]

comments appreciated. no changes anticipated. all sockets on spur are permanently plugged in items , vivarium, aquarium, PC, TV, 2 table lamps, all low power appliances. no heating, occassional hoover.

 

[nickblake]

When you look at whats being used on a general circuit (not the kitchen ) then its very little may be a bedside light pc etc so id do as malcome has said derate the MCB to a 20 amp lable the board and identify on EIC

 

[telectrix]

thank you both, malcolm and nick. just got to remember to unplug pc and tv before IR test!!!!!

 

[JUD]

There is nothing stopping you wanting to fit a smaller protection device to the ring, though appendix 15 does clearly state what a ring final circuit is and denotes the protection as being 30 or 32 amps. So you would mark that on your EIC as a departure from the Regs and as your fitting a smaller protection device on a rated cable your not going to make the installation less safe and should be ok. Reg 120.3

Though if it was me you have no need to do anything really. As your fitting a new CU then all you need to do is make your work in line with the 7671. Again on your EIC you note in the part comments on existing installation the spurs and advise the client that they do not come up to the Regs and you advise them to have them upgraded.

Appendix 15 is Informative and does not form part of the regs so down-rating a ring to 16A is not a departure IMO.

I would just note it on the cert. that it is a ring to avoid confusion in the future.

 

[malcolmsanford]

Informative it maybe but as we wire ring final circuits in a minimum of 2.5mm we adhered to it.
Informative it maybe but as we still connect a ring start and finish at the CU we adhere to it
Informitive it maybe but as we feed one single or double unfused spur per socket it's adhered to.
Informative it maybe but as still advised RCD for additional protection under 411.3.3 522.6.6 and 522.6.5 we adhere to it.

And about 3 other informative parts we adhere to ,so when you derate a ring final from circuit from 30 or 32 amp it is a departure, well to me it is and should be noted

 

[sjm]

Completely agree with JUD. If you're worried about 16 amps can you not use a 20 amp mcb?

 

[telectrix]

think i might split the ring and make it into 2 radials. 16Aeach, one on each RCD, no departures, less problems with nuisance trips. everyone's a winner!

 

[JUD]

Informative it maybe but as we wire ring final circuits in a minimum of 2.5mm we adhered to it.
This is a matter of current-carrying-capacity of cables, not the size of the OCPD.

Informative it maybe but as we still connect a ring start and finish at the CU we adhere to it
If it didn't start and finish at the CU it wouldn't be a ring circuit.

Informitive it maybe but as we feed one single or double unfused spur per socket it's adhered to.
Again, a matter of current-carrying-capacity to avoid overloading cables.

Informative it maybe but as still advised RCD for additional protection under 411.3.3 522.6.6 and 522.6.5 we adhere to it.
You are adhering to the above regulations, not Appendix 15.

And about 3 other informative parts we adhere to ,so when you derate a ring final from circuit from 30 or 32 amp it is a departure, well to me it is and should be noted

For something to be a departure then it needs to be a departure from an actual regulation.

Appendix 15 is not a regulation and AFAIK there are no regs stating that a ring circuit must be fed from a 30A or 32A OCPD.

 

[telectrix]

JUD, i like that post

 

[malcolmsanford]

Then nor are any of the appendix regualtions then as they are all informative.

Appendix 12 does not quote any regulation to adhere to or conform to. It does give values from a table but it never refers to a regulation, but we still work to it.

I must be in a vast minority as I have yet in all the years I have worked in the industry seen a design for a 20amp ring final circuit. Nor have I worked on a installation that as had a 20amp ring final circuit and I doubt I will. So if it's not forming part of the regs it is certainly non conforming to traditional design, perhaps we should note it under 120.4 as NEW INVENTIONS

As I have said I have no problems with a 20amp ring final circuit and if you want to be perdandtic then yes it might not be against the regs, but it states informative or otherwise that a ring final circuit should be 30 or 32 amps and I would personally mark it as a departure on an EIC.