Feeding a out building 77mtrs

[springfield]

Hi All,
Am installing a ring circuit of 5 sockets,10 x 5ft twin flourescents & 6 x 400w pir flood lights into a outbuilding used for storage. I am thinking a 10mm 3 core swa will be suitable.

The run is 77mtrs. Am going to stick a 40amp RCBO at main fuseboard and a rcd board in the outbuilding.

Is the 10mm 3 core swa cable suitable for the above loading/distance.

 

[micknew]

Best do a course on electrical installation and calculations and get qualifications required to carry out the works..
The installation would need testing and a Part P certificate.

 

[Octopus]

me thinks you'll have discrimination problems

 

[johnboy6083]

max vd = 3% of 230 = 6.9
max mV/A/m = 6.9/(77x35) = 2.56 mV/a/m(i used 35A as Ib, no diversity applied)

so 10mm is not suitable, but 25mm2 is.


whats your Ze at the main board, so we can see iof iot will meet disconnection times?

 

[johnboy6083]

me thinks you'll have discrimination problems

i agree, you will have discrimination problems. It would be better to feed the outbuilding from a BS88 fuse. that way your overload protection will discriminate.

Even if you still choose not to go with a fuse at the supplyu end, an RCBO-RCD is not advisable. The only way you will achieve true discriomination with RCD's is to use S-type. It will be much more cost effective to go with the fuse.

 

[Octopus]

i agree, you will have discrimination problems. It would be better to feed the outbuilding from a BS88 fuse. that way your overload protection will discriminate.

Even if you still choose not to go with a fuse at the supplyu end, an RCBO-RCD is not advisable. The only way you will achieve true discriomination with RCD's is to use S-type. It will be much more cost effective to go with the fuse.

I really dispair people here clearly giving all the answers to DIYers. Every time this happens you are damaging the trade.

 

[johnboy6083]

to be honest, the amount of sparks i see who dont know how to do this depairs me. Its sad that i didnt even think to see if it was a DIYer. I assumed it was a spark.

Most sparks i work with, only know how to read the standard circuits listed n appendix 8 of the OSG.

 

[topquark]

What is the rating of the fluorescent tubes? What are your earthing/bonding arrangements to be? (you may need 4 core swa as using the armour for your earth may not be sufficient if it works out that you need 16mm, depending on the type of swa sheathing).

You should just use an MCB at the main "fuse board" as you are intending to use RCD protection in the outbuilding.

 

[micknew]

Totally agree, B&Q must love this website!!!!
The site for advice for DIYers.

 

[clicon357]

Case in point, my best mate (a chippy) rang up one time, the conversation went roughly like this:

"I'm after a bit of armoured"
"What for?"
"The hot tub, the bloke said either 4mm or 6mm will do?"
"What bloke?"
"The hot tub bloke, he said if I run the cable their "electrician" will connect it"
"Well how longs the run, what load?"
"I ran a bit of string down the garden and its 33m"

He came down to my place with his bit of string. I measured it at 27m". I did a quick calc and gave him a length of 6mm and off he went. The hot tub people came in. Fitted a new 32A breaker to his existing board that stuck out too much, closed the clear plastic lid on it and broke one hinge. At the end of it all no certs given either! My mate and his missus paid by cheque as well. The hot tub install cost them £8K. Said he should take it up with them but he's too nice? Mind you he's also been caught twice by people phoning up and asking for his bank details.

It's a tricky one especially with friends and family do you try and help to a point or let them go and fit the length of 2.5 SWA they nicked from work?

My own brothers attitude to outside power - two extension leads run the length of the garden. The reel of one and the plug of the other jammed up a plum tree and covered with a couple of Sainsbury's bags. I HAD to say something I mean I might need a kidney one day!

IMO places like B&Q should only sell to someone upon presentation of qualifications / proof of competency at the till!