Feeding a sub main

[stripes]

Hi all,

I have been asked by a friend to quote for a new consumer unit and additional sockets in his home, all pretty bog standard.
However, he is having the original brick built sheds to the outside of his house turned into an bathroom and passage way.
He wants sockets and lights inside the passage way, outside socket, lighting in the bathroom, shaver socket etc.
All the quotes he has received so far are to replace his consumer unit and run a 6mm cable straight from a 40A mcb form the c/u through the houses front canopy (which is be built also) into the passage way at the side of the house to feed a sub main for the new circuits.

I think the supply should be from the supply tails into a Henley block to a Main Switch with cartridge fuse, then run a 6mm cable from the main switch to the sub main, its only a 10m run.

Am I over complicating it?

Would like to hear your thoughts.

 

[telectrix]

nothing wrong with method 1 if you have the 40A MCB non-RCD and fit your RCD protection at the sub. ( providing you don't contravene 522.6.101.)

 

[Toby Kuhnert]

That's how I would do it in an ideal world! where you have enough space

 

[Guest55]

both methods are acceptable.
ultimately depends on your friends budget.
i'm assuming theres no spare way in the existing CU ?

 

[dazza1981]

Hi stripes
Can i ask why you think it would be better to split tails in henley block and use a cartridge fuse???
Is it shearly because theres not enough space??

 

[Toby Kuhnert]

IMO using a cartridge fuse allows for better discrimination

 

[stripes]

Hi stripes
Can i ask why you think it would be better to split tails in henley block and use a cartridge fuse???
Is it shearly because theres not enough space??

Hi,

He has a 16th board with no spaces, so will replace with 17th split load board. The service head is on the opposite side of the house to the new bathroom, passage way and utility room, so can't wire up direct to new c/u.
I suppose the cheapest option is to wire 6mm straight into a 40A MCB on new board.

 

[Engineer54]

So not even considering extending the upstairs RFC (that will typically be under loaded) and upstairs or downstairs lighting circuit to supply these two additional rooms, just bung a submain to a separate Garage type CU. Typical thinking of a electrical trainee!!

 

[Risteard]

IMO using a cartridge fuse allows for better discrimination

It's a fact.

Two BS EN 60898s in series are rubbish for discrimination in a fault.

 

[stripes]

So not even considering extending the upstairs RFC (that will typically be under loaded) and upstairs or downstairs lighting circuit to supply these two additional rooms, just bung a submain to a separate Garage type CU. Typical thinking of a electrical trainee!!

No, not just banging in a sub main, the bedrooms have had new fitted carpets and then had fixed wardrobes fitted over the carpets, so I don't have the ok to lift them, the loft has had a dodgy loft conversion, and it is used us a bedroom cant lift the boards there either, have no option but run a cable.

 

[jeremy]

You can get din rail mounted cartridge fuse holders, which would give you a combination of both solutions, we use them either from Hager (BS), or Schrack (EN). Hagers are sized, ie a 5 amp fuse wont work in a 20amp holder, Schrack's are just one size.

 

[Engineer54]

No, not just banging in a sub main, the bedrooms have had new fitted carpets and then had fixed wardrobes fitted over the carpets, so I don't have the ok to lift them, the loft has had a dodgy loft conversion, and it is used us a bedroom cant lift the boards there either, have no option but run a cable.

I don't know, ...dodgy fitted wardrobes (if fitted over carpet), dodgy loft conversion and now a possible dodgy electrical installation, not having much luck your mate!! lol!!

So what's the problem with lifting the new carpet and floorboards then?? No idea why you would need to get into the loft??

 

[Kate]

Im not a Electrical Trainee wonder and i personally wouldnt want to lift brand new carpet either if there was another option.

Engineer 54 said about upstairs lighting circuit..so would need to go in loft for that. Feel stripes was just saying about it all, not saying he had to use upstairs lighting.

 

[Kate]

My thoughts...

If you are already changing fuseboard you will be able to plan to have a spare way so thats not an issue. For one bathroom and a hallway to have its own submain is a bit much.

 

[Engineer54]

Im not a Electrical Trainee wonder and i personally wouldnt want to lift brand new carpet either if there was another option. There are ALWAYS options, but still can't see a problem lifting a small to large area of new carpet...

Engineer 54 said about upstairs lighting circuit..so would need to go in loft for that. Feel stripes was just saying about it all, not saying he had to use upstairs lighting.

No, i was thinking along the lines of grabbing the supply up to the loft, at upstairs floor level. Just as easy to use the downstairs lighting circuit, ...3 or 4 extra points isn't going make much of a difference to the circuit make-up, especially if were talking LED lamps and fittings!!

Anyway, There always seems to me to be excuses put up, as to why they can't possibly use existing circuits for any extension work, it always has to be a sub-main CU.