old electric feed not up to scratch.

[topbanana]

have looked through previous posts and can't find anything exactly like mine so would like to make sure.if you can please help i'd be most grateful.
Have a schupa box with a 63A,30mA rccb, controlling 1no 30a,1no 20a, 1no 16a,and 1no6a,mcb's.
the 16a mcb is for a feed to the garage some 27metres long through the ceiling void and eventually out into the open, non conduited, to the garage.
I've been fitting the bathroom and kitchen at the property and asked why this particular mcb was always off.-- it seems that after some builders were working in the upstairs flat some time ago, also owned by my client, the mcb tripped and couldn't be put back on.
I cannot get to the cable now without ripping down the ceiling, as i beleive on looking at a part of the upstairs ceiling void there are a few nails protruding through the floor to no purpose.
i beleive they punctured the cable, and would like to replace, but the cable is so tightly jammed into the slots in the timber i won't be able to run another through by pulling the old one.
My other option is to run a cable externally from the c.u. along the sidewall of the house to the garage.
at present it runs to some bad shape sockets in there, which i'd like to replace with a shed c.u.,powering a light and a socket mcb, with one new socket.
here's my question at last.
what cable do i use--- it appears 4mm swa is talked of previously!
i would like to have some protection in the garage as the tenant of the garage might not be the same as the tenant of the downstairs flat. What could i install to ensure this if possible.
thanks for looking at this.

 

[Adam_151]

done some quick calculations and I'd guess that you'd be looking at 4mm² SWA for a 20A submain and 6mm² SWA for a 32A submain at that length, both of which will drop 2/3 of the allowed voltage drop at full load* so as long as you keep your final circuits shortish...

Whats this about 'protection'? RCD protection, yes it'll be neccesary for the sockets, but you have that, because you are looking at feeding from an RCD protected board, and whats this about different tenants, is the flat tenant happy that he is paying for the garage tenants electricity, and is the garage tentent happy that he can't reset his RCD protection (regardless of anything else, I'd recommend swapping to a split board, garage on non-rcd, and rcd board in garage), and his overcurrent protection? (or have I mis-understoof totally)



(* actually in realitiy it'll be less than this, because you arn't maxing out the current carrying capacity of the cable, and thus it won't be at 70C, but thats difficult to quantify)

 

[topbanana]

Thanks for your help.
Yes i understand the possible conflict between users and payment.
The thought was a secondary meter could be put on the supply to the garage. which i am now told is going to be back in the use of the tenants after a short time.

 

[plugwash]

you can buy refurbished meters pretty cheap e.g. http://www.tlc-direct.co.uk/Products/RDCRED60.html

meters are designed for connecting to meter tails, if you wan't to use them with other types of cable (e.g. your swa) you will have to butt something (many use an adaptable box but if you were carefull you could probablly use the garage CU) against the bottom to ensure that any individual single insulated cores are enclosed.

 

[topbanana]

cheers for the advice. i'll keep that address.