Sub mains question

[Sparkycuv]

im going to run a submain.

i got the idea of running the main tails from the meter into a SP+N 100A switch fuse unit then submain tails from that upto the flat.

there are several flats in the building so is it best to fuse it with one of the units so the cable is not just reliant on the leccy boards fuse.

i have had a brief look at the current wiring in the basement "load centre" each flat is individually fed with a wylex switch fuse. ( im probably answering my own question with that comment)

so situation A = meter tails to 100A switch fuse unit then on to flat

Situation B = meter tails to 100A 60947-3 isolater switch reliant on main cut out fuse.

im probably just over thinking the whole thing

 

[ericmark]

You as the designer have to decide the best route but some questions and pointers to ask yourself.

If the DNO supply is feeding multi-flats then to fit a fuse to each flat would make sense but in that case how will the tenants be billed for the power they use?

If it is feeding a single flat why would you want to duplicate the fuses? If it should blow how would the tenant know if he needs to change a fuse or if he needs to call DNO?

Where the fuse is under size as with caravans on a caravan site then there is a case for a slightly small fuse/MCB that the user can change mainly as it is likely to open many times a year. However one would hope the fuse supplying a flat would be big enough for the normal day to day use and one can expect 10 years between fuse changes and even then only due to changing meter. So why duplicate it?

 

[Lectrician]

I assume there is a row of meters and a row of switch fuses. This is the common way.

The main point to consider?

How are your 'tails' to be installed upto the flat?

There is now a requirement to RCD protect (30mA) cables buried in a wall at a depth of less than 50mm - that would include standard stud walls, and include short drops up or down to a CU.

You can use SWA, MICC, Flexsheild, steel conduit, steel trunk etc in order to remove the RCD protection - your tails WILL need protection.

Unfortunately adding a 30mA RCD to the front of the installation would not comply either! There is a need to minimise inconvenience and danger by splitting the circuits across atleast two RCD's.

 

[Sparkycuv]

Theres 10 flats all in all, ten individual meters, these then go into a wylex isolater with cartridge fuse. From this isolater its a 16mm twin and earth cable to the flat which is embedded in the wall and possibly clipped up a fire escape there are several already there. Im wanting to replace this with a swa cable so earthed metallic sheath protects the cable and no need to rcd and cause inconvenience tenant. I've seen the rule in the regs about it. I already install dual rcd boards and i understand about splitting up circuits into groups to minimize inconvenience

 

[Sparkycuv]

apologies to all, i was stupidly vague in my initial post!! currently using a mobile with internet so this is a chore to type. current submain is a 16mm t+e, it is embedded in the wall. It is protected by a wylex isolater with cartridge fuse. This is located in the basement along with the flats "own" meter. Proposed plan is to replace with a steel wire armoured cable and protect the cable with a new wylex 100A isolator. Old one is rusty and ancient. New "dual" rcd board will be relocated to a proposed utility room and will replace ancient BS3036 fuse and the current board is currently 2.4m off floor level. Any helpful advice or does this sound ok

 

[Spark123]

Your setup will depend on the DNO, some only allow a maximum meter tail length of 3m to be protected by their fuse.

 

[Sparkycuv]

Your setup will depend on the DNO, some only allow a maximum meter tail length of 3m to be protected by their fuse.

i've done it again and missed a bit out. the 100A isolater would contain a BS1361 100A cartridge fuse

http://www.tlc-direct.co.uk/Products/WY110M.html