Workshop/hobby Room Electrics

[supaev]

Hi I am 67 and retired. I was  qualified accountant but always wanted to be an electrician when I was at school. I bought my first house in 1972 which I rewired myself - regulations were less strict than they are now. I don't know whether it has been rewired since but it hasn't burnt down yet!

We are renovating our present old house and getting an electrician to do a partial rewire in stages. Ha has already put in a 16 MCB dual RCD CU and we have had a new digital meter fitted by the supplier and the DNO has uprated the main fuse from 60amp to 100amp. The electrician has also put in 3 new circuits and passed the whole house. All the cables downstairs (ring main, cooker and outhouse power are underneath the concrete floor and have been for 30 years which isn't the best.

I have a garage sized outhouse which houses my model railway. Forgetting the existing power set up I would like our electrician to do the following :- Starting at a 32 amp MCB in house CU , then 6mm sq  SWA via metal box & gland all the way to outhouse clipped to a convenient brick wall and then into small CU in outhouse again via metal box and gland. This CU not to have an RCD as covered by main CU but DP 40amp switch with at least 2 MCB's , one 6 amp for lighting and one 32 amp for outhouse ring main. This consists of 3 double sockets on the 2.5mm sq ring with 2 separate sockets spurred off.( incl. one to an adjacent shed.). What I want to do is run a 6mm T&E from the 32 amp breaker in the outhouse CU to a 45 amp DP switch and then connect both legs of the 2.5mm sq ring to this switch. So I will be able to switch the power ( and lights) off when I leave the outhouse without touching the CU. Sorry to be so long winded but you need all the facts to let me know that this should comply with regulations if done by my electrician.

 

[sparkytim]

Sounds ok but it may be better to have an RCD at the Out house end as the SWA does not need RCD protection (Unless a TT earthing sytem in use for the House)

Why not just use the Outhouse Consumer Unit Main switch / RCD to switch it all off as you leave?

 

[SPECIAL LOCATION]

Why not ask your electrician?

Why the 32A ring circuit for 3 double sockets?

Why not a 20A or 16A radial? 

What are the actual proposed loads?

Why not position the outhouse CU so that can be switched as you enter / leave?

What is your existing supply earth arrangement?

:C

 

[supaev]

Sounds ok but it may be better to have an RCD at the Out house end as the SWA does not need RCD protection (Unless a TT earthing sytem in use for the House)

Why not just use the Outhouse Consumer Unit Main switch / RCD to switch it all off as you leave?

At the moment we have two RCD's on this circuit which causes nuisance tripping and there are no unprotected ways in the Main house CU. I have read about the various earthing systems but I am not sure what we have - just the usual domestic supply with a flat braded  earth connection on the DNO fuse ., but this presumably won't impart much information to anybody. My electrician will be doing this and I expect he will export the house earth to the outhouse via the third inner of the SWA & bond this to the SWA armour as well as there is nothing metallic such as gas or water pipes in the outhouse. Re. using the outhouse CU main switch I thought these were just for occasional use for isolation purposes not for heavy use ( could be several times a day).

 

[SPECIAL LOCATION]

At the moment we have two RCD's on this circuit which causes nuisance tripping and there are no unprotected ways in the Main house CU. I have read about the various earthing systems but I am not sure what we have - just the usual domestic supply with a flat braded  earth connection on the DNO fuse ., but this presumably won't impart much information to anybody. My electrician will be doing this and I expect he will export the house earth to the outhouse via the third inner of the SWA & bond this to the SWA armour as well as there is nothing metallic such as gas or water pipes in the outhouse. Re. using the outhouse CU main switch I thought these were just for occasional use for isolation purposes not for heavy use ( could be several times a day).

Two RCD's does not cause nuisance tripping....

faulty appliances or cable faults cause an RCD to trip...

BUT two on the same circuit is poor/daft design as there will be no discrimination and it will be pot luck as to which one will operate when there is a fault condition....

Your Earth sounds like it could be TN-C-S ...

may not be wise exporting the earth...

you electrician should be aware of the various complications limitations...

also the fact that a BSEN60947 isolator switch can be used for both functional and emergency switching if required...

But if you are concerned about using a heavy duty switch, why not put the sockets off a 20A radial

then fit a double gang grid switch with a 20A DP switch for your sockets next to the light switch in the same back box?

If I were you I would give your electrician a spec of what you want and leave him to design it correctly for you.

:coffee

 

[supaev]

Hi Trailer Boy

I will ask my electrician when I can get hold of him!

The present set up which I do not wish to alter much in the shed due to the model railway filling it.

is as follows:-

16 amp MCB in new house 16 way CU via 30 year old 2.5 T & E under concrete floor ,20 amp DP switch on kitchen wall at point of egress 16 or 20? amp rubber covered flex through hole in wooden window frame (soon to be replaced) , then outside on ground in flexible outdoor plastic conduit though hole in shed facia , to junction box converted to 2.5 T & E to 20 amp DP switch to ring in 2.5T & E with 3 double sockets and one spur in shed and one spur to adjacent wooden shed. With heating for one outbuilding sometimes one shed,9 lights , 10 transformers for model railway and use of power tools  etc.I want a supply from a 32 amp MCB in the Main CU. This was the reason plus new electric shower that  I gave the DNO to get the main fuse increased from 60 amp to 100 amp. If I am getting the upgrade done INHO the extra expense  in having 32 amp instead of 16 amp is justified in that it covers all future use. If the house was eventually sold it would be sold with detached workshop. Thank you for the information given it will help in discussing it with my electrician to get the optimum solution.