Help, multiple circuits external supply 7 core SWA

[typical.me]

Hi guys, i've also posted this on another forum. sorry!!! but wonder if you could help,

I have been asked to supply power and lighting to a cabin/summerhouse 35 metres from house C.U.

Customer has already installed 7 core 2.5mm SWA underground (he says he "acquired it" from a friend at YEDL)

All calculations are fine for a load max of 2Kw (volt drop approx 5.9v)

My problem is, because it is 7core, the guy wants to include within it, a seperate lighting cct for tree illumination, controlled at the house end when the cabin is isolated.

Just like to know your thoughts regarding safe isolation at house end for anyone in the future working on either circuit, i.e. how you would supply both circuits.

1) from 2 seperate spare ways in c.u. suitably protected

2) create a distribution circuit, either 25mm tails & henley block or 6mm from c.u, to a 2 way "garage" cu and then feed from there within the swa (adaptor box if nescessary)

Also, sorry to be a pain, your thoughts on protection at cabin end.

System is TN-S

No extraneous conductive parts at cabin end

Sorry for long post

Thanx

Mick

 

[sparkytim]

How are you planning to use the 7 cores?

If spares are available why not use 2 cores as a switch pair back from cabin for the lights he want's to switch from house.

 

[Badger]

id take the armoured to a garage c/u 2way, with main rcd 30 ma trip and 20 amp and 6 amp mcbs, that way the armoured can be isolated by turning off the rcd main switch, also put a note on the c/u to make any future sparks realise that 7 core is fed from that board and that 2 supplies are present in one cable, one last thing use 2 cores for the live and neutral on 20amp trip and 2 cores for 6 amp circuit live a neutral, because sharing the neutral on one conductor could be dangerous.

 

[Apache]

All calculations are fine for a load max of 2Kw (volt drop approx 5.9v)

Isn't it max 3% VD for lighting?

 

[typical.me]

Hi Apache, thanx for reply,

yeh it is 3% for lighting, but i was more concerned about the isolation set up inside house, forgot to state load for lighting.

lighting i have calculated at absolute top end max 1Kw, 4 x 100 watt lamps a couple of elv circuits, and expansion

volts drop 18milliohms/metre x 35metres x 4.35amps = 2.7%

You got any thoughts on the set up inside the cabin if RCD protected at house end,

cheers

mick

 

[Apache]

You got any thoughts on the set up inside the cabin if RCD protected at house end,

Pretty much what you have said! How much space have you got in the house CU - can you spare 2 ways, one for the tree lights and one for cabin?

If so do as has been suggested and use as switched pair down the SWA. I'd whack a DP isolation in the house so worse case you can still reset your RCD!

7 cores

L - cabin

N - cabin

E - cabin

swL - tree lights

N - tree lights

E - tree lights

and 1 spare core.

Just label things up clearly.

 

[typical.me]

Thanx Apache,

yeh i have 2 spare ways in house c.u. so,

2 x mcb at house to supply the following:

1 x mcb to supplying swa direct to cabin where a garage type c.u. to be installed RCD protected at cabin end, not house end.

1 x 6 amp mcb from house cu feeding a double pole isolator, switching the "tree lighting" fed via same swa.

I am probably completely wrong here but,

got problem there me thinx, cos outside lighting has to be rcd protected

so will have to RCD/RCBO the lighting circuit.

I could RCD protect both circuits SWA at house end, however any rcd tripping would mean a 35 metre walk back in the dark!!!

Shoot me down in flames cos i am having a mare!!

Thanx for replies guys

mick

 

[Apache]

I am probably completely wrong here but,

got problem there me thinx, cos outside lighting has to be rcd protected

so will have to RCD/RCBO the lighting circuit.

I could RCD protect both circuits SWA at house end, however any rcd tripping would mean a 35 metre walk back in the dark!!!

Shoot me down in flames cos i am having a mare!!

Thanx for replies guys

mick

RCD needed for portable equipment use outdoors, but not fixed wiring. Not such a bad idea.

My thoughts on this - if the RCD has tripped it has potentially just saved your life, be glad of the 35 meter walk to calm down having just cut the hedge trimmer cable!

The RCD should only trip if there is some problem. Mine haven't been tripped in 4 years in this house. I do tets them occasionally.

I think the walk back is a crappy argument! That said if you run in SWA you only need RCD at the shed end.

 

[muffin]

id personaly put a 4 pole rotary isolator adjacent to the house db, switching off the two supplys. and a clear warning notice should be fitted