Another cable sizing question

[ABerry82]

i have been asked to install a garage unit in a outbuilding they wanted a couple of sockets and lights and i think i allowed about 20A total output for design current. what size cable do you think bearing in mind its a 90 meter run in a trench from house to out building.i allowed 16mm does this sound like overkill

 

[Engineer54]

Your customers seem to have some very Big back gardens up in Yarmouth!! lol!!

 

[aaelectric]

16mm is more than enough and leaves enough to add on in the future.

 

[DPG]

Your customers seem to have some very Big back gardens up in Yarmouth!! lol!!

Excellent! Daz

 

[Engineer54]

How much are you charging for that 90m 500/600mm deep trench?? Got to be worth hiring a mini digger for that sort of distance...lol!!

 

[ABerry82]

Your customers seem to have some very Big back gardens up in Yarmouth!! lol!!

customer lives in martham

 

[ABerry82]

the 90m was her estimate. i did go to neweys to get a quote for both 16mm an 10mm swa. but i think i will go round and measure up for my self as swa isn't cheap

 

[trev]

Rather than asking us, do your cable calcs tell you this will be ok? If they do it'll be fine, if not then pick the appropriate size

 

[Wayne Watts]

Are you suggesting 16mm on a rule of thumb or have you calculated it taking vd into account? It may seem overkill but a 5% or 11.5 volt drop on a 230v single phase supply from supply cutout to your outbuilding will require an apparently large cable. I would normally design a sub-main vd calc on 2.5 to 3% so you can have allowance of around the same on your final circuits. Enjoy!

 

[GLENNSPARK]

why have you allowed 20A?.....assume your going to use a 16A MCB...for the outlets....and a 6A MCB for the lighting......thats 22A mate.....

 

[trev]

How much are you charging for that 90m 500/600mm deep trench?? Got to be worth hiring a mini digger for that sort of distance...lol!!

OI! The apprentice is not for hire! And don't call him mini, he's vertically challenged

 

[Jimmyb]

16mm is the smallest i would use as that is 5.04 vd and max for lights is 6.9 so 10mm will be over this

 

[D80]

What type of "Garage"? If its one you park cars in then fair enough, but the 90M walk to the house in a winters nights is a bit of a nightmare. In fact a nightmare at most times. 20Amp probably enough there, its not like they will be putting tumble dryers or washing machines in it that far from the house.

If it's a garage to work on cars/projects etc then 20Amp may be shy, could be the likes of a welder going in. I'd visit site, get a proper spec of what is going to be used out there and a proper distance from the house. Customer estimates on distances and the like tend to be well off and there is no point in wasting your own time sizing and pricing up cable until you know what you need.

 

[telectrix]

why have you allowed 20A?.....assume your going to use a 16A MCB...for the outlets....and a 6A MCB for the lighting......thats 22A mate.....

but that's the MCB ratings, not the design current. would need a lot of lights to pull 6A.

 

[malcolmsanford]

and the earthing system is .............................ok i'll get my coat