Newbie question - new ring

[Dinth]

Hi. Im trying to design a new ring final circuit for my loft. Can someone please have a look on this draft and assess if there's something wrong in it, etc? I've got no experience or knowledge in electrics and dont know much about Building regs.
Im especially worried about using MCB's and a small consumer unit in "ring final circuit". Im also curious if i could use 40A+ protection for this ring or 32A is the highest protection possible in RFCs?

 

[mwatsonxx]

I can't see any ring circuit. What are you trying to achieve? why are you doing this? there maybe simpler solutions.

 

[Dinth]

Hi, maybe my schematic is not very clear - the ring is between CU, two 13A double sockets, fused spur box and a distribution point with three MCB-protected spurs, unless ive made some mistake of course.

I need to run electricity to my loft, where i need it to power the following appliances: fixed combi boiler, two 16A industrial sockets (in constant use), two 13A domestic sockets (in constant use) and an extra sockets for connecting vacuum cleaner, etc would be nice. Obviously those appliances would be near the center of the ring. The load of the circuit may occasionally exceed 7600W.

In the future i want to upgrade two 16A sockets and two 13A sockets with Z-wave high-current relay switches - that's why i've used spurs for them instead of including them in the ring.

Ive got only two 25mm oval conduits under thermal insulation available to run the cables through, so i cannot use a cable larger than 4mm2 T+E. Also i dont want to worry about the cable catching flame in my insulation, so i've assumed that ring will be better as it has higher current capacity than radial.

 

[Taylortwocities]

Sorry to rain on your parade...
You cannot do what you want like that.
Ring final circuits are not designed for that.

You would need to run a single cable to the CU in the loft - probably 10mm - and have a 40A MCB in the downstairs CU.

So

Ive got only two 25mm oval conduits under thermal insulation available to run the cables through, so i cannot use a cable larger than 4mm2 T+E.

You are up a gum tree then. You need to have a rethink.

Oh and plus. You are considering several new circuits.
this is notifiable work. So you'll need to get a building notice raised with the LABC who will expect that the whole thing will hav e been designed and installed in accordance with BS7671. You cannot do that as you obviously do not have a scooby on this.

Better (and cheaper) for you to get a registered electrician to do it for you.

 

[winston1]

A new circuit is notifiable. Have you done that?

Rings are wired in 2.5mm cable on 32 amp MCBs, not 40 amp, so you can't have 7600 watts.

You have 3 spurs all of which are greater than a 13 amp load. Don't believe this is allowed.

I'm not even going to ask why on earth you need 2 16 amp sockets in a loft.

 

[EFLImpudence]

Good grief. What a mess.

Start again.

 

[dobby1]

God Almighty. Keep it simple; one run between the two CUs, and feed the loft off the secondary CU.

Also, you will need at least 10mm^2 for the main feed if you plan to use 7500w. 4mm^2 is rated at about 25a/5750w if running through an insulated wall. Unless you want to potentially burn your house down.

Are you running a server farm or something?

 

[Dinth]

Better (and cheaper) for you to get a registered electrician to do it for you.

Fully understand, but still - I will need to show him a schematics of what i want to do, as it isn't a "normal" domestic job with all the relays etc.

 

[Taylortwocities]

Take a step back. Just explain your requirements. He/she will do the detailed design.
At the end he has to sign an Electrical Installation Certificate that says that HE has designed, installed and tested the whole enchilada in accordance with BS7671.
So you cannot give him your design to install unless it complies with BS7671.

 

[mwatsonxx]

Are you running a server farm or something?

More like a wacky baccy farm

 

[Dinth]

Are you running a server farm or something?

Indeed. Not a farm though, just a bunch of normal servers, home network, home automation, etc

 

[mwatsonxx]

So where is all the electrical load coming from?

 

[Taylortwocities]

…

 

[Dinth]

…

So where is all the electrical load coming from?

OK guys. Thank you for all your help. You made me realize that my idea of this circuit was completely wrong and overcomplicated(!). I've rethinked this i basically i can connect the boiler and one socket (which are located on the wall opposite 16A sockets) to the existing ring, and just get someone to run a 10mm2 cable between CU and my loft (maybe even it will fit existing 25mm oval tube but i doubt it )

 

[Taylortwocities]

He/she will not only need to to run the cable. Also, connect it at the existing CU, create the new CU in the loft, create the new circuits, test everything. Certificate it all, notify LABC....

Just looking at your plan 1. What is your plan re RCD protection of, well, anything?