30 amp rewireable fuse + 1.0mm cpc

[Des 56]

Having been one of the culprits who wired 2.5 ring mains with 1.0mm cpc in times past
I am going to do some repositioning of sockets in a kitchen which is being extended
It has rewireable fuses pre-dating the standard wylex rewireables

Before taking on the work I tested the existing ring and looked in the good book for max zs because there is no chance whatsoever of rewiring for various reasons
Having in the past seen and used 30 amp fuses for these on numerous occasions,I was surprised they appear to be not listed in the on site guide
The way I am reading it,30 amp fuses on a 1.0mm cpc ring are not permitted
(Having said that working my way through guide books has never been a strong point with me)

Is this correct or am I cocking up somewhere?
The only reason I can come up with is possible thermal effects on the 1.0mm cpc

Your advise and/or knowlege would be greatly appreciated

 

[scotsparky]

Des 3o fuses and 32a mcb,bs88 (with rcd protection) is ok.

With rings it is esentially a duel supply to each point so its 5mm and 2mm cpc.
As its a ring what is assumend on a perfect situation is 16a load per leg to md pot so your "2.5d 1mm cpc is allowed. If in dought try the adiobatic to prove ring size section its arround section 520530 of BRB

 

[andyb]

Table 41.2 of the brg, max Zs for a 30 amp fuse to BS 3036 1.09 ohms.
Appendix 15 conductor size of ring, live=2.5mm, cpc=1.5mm

However, 433.1.3 say where the protective device is BS3036, you must de-rate the current carrying capacity of the cable by 0.727.

So, add this to the need for rcd protection, you should change the protective device to an rcbo or better still fit a new consummer unit.

As to wether you can extend a final ring circuit that has a 1mm cpc rather than rewire the whole circuit.................

I dont know!

 

[Des 56]

Thanks for the reply scotsparky
I have done the adiabatic and its ok
What was throwing me was the statement at the bottom
The combination of the protective conductor and the fuse is not permitted


If I assume equal load down both legs and 2x1.0mm cpc then the statement does not apply?

Table 41.2 of the brg, max Zs for a 30 amp fuse to BS 3036 1.09 ohms.
Appendix 15 conductor size of ring, live=2.5mm, cpc=1.5mm

However, 433.1.3 say where the protective device is BS3036, you must de-rate the current carrying capacity of the cable by 0.727.

So, add this to the need for rcd protection, you should change the protective device to an rcbo or better still fit a new consummer unit.

As to wether you can extend a final ring circuit that has a 1mm cpc rather than rewire the whole circuit.................

I dont know!

There is an existing 30 m/amp rcd and the main earth conductor and protective bonding are to standard
The lenghth of circuit will not be extended as such
I have suggested a new consumer unit,but the soon to be kitchen fitter has already agreed with the householder to fit one later on(thats one reason why I am checking the compliance before commencing the work, I may have reason to quote for the consumer unit before him (defined scope or not he is taking work off me,maybe work he should not be doing )
I will be working for a builder and will do whats required for him,but my install/alteration needs to be correct ,new consumer or not,but the guide threw a panner at my understanding
Thanks for the replies