SWA long 140M run please help!!

[FCC5206]

Evening all
I have been asked what size cable will be required for a long run. I know there are heaps of threads on here from people too lazy to do their homework but I have and am still lost so sorry if this has been covered i just cant find the answer.
The run is to power a stable block which the customer has told me needs power equivalent to a 2 bed house!!
The length of the run is 140 meters!
Taking into consideration max demand and diversity after doing my voltdrop calcs i come up with a 2 core 95mm2 to achieve the required 5% drop!! I know this is absurd and was wondering if anyone could point me in the right direction

Thanks

Chris

 

[Guest55]

ok , have it your way.
;-)

 

[Engineer54]

ok , have it your way.
;-)

I will ...lol!!:yes:

 

[Guest55]

I will ...lol!!:yes:

nice trolling , touche lol.

 

[Engineer54]

nice trolling , touche lol.

Think i'll leave the Trolling to you, that's your dept after all!! I don't want to step on anybodies toes. ...lol!! :teeth_smile:

 

[Guest55]

Think i'll leave the Trolling to you, that's your dept after all!! I don't want to step on anybodies toes. ...lol!! :teeth_smile:

theres plenty of trolling to go round , just think of it as xmas goodwill.
;-)

 

[FCC5206]

Hello I didnt mean to start an arguement!

The guy has been back to me saying DNO is not an option "what power could i have down there"?

Could someone please check my calcs if im honest I dont think the job will come my way as he wants a bodger to throw a cable in but the maths is well worth me doing!!

Its based on a 150 meter run with 2 core SWA buried.

25mm 11.5 volt drop at 40 amps/ 6K watts
35mm 11.5 volt drop at 55 amps/ 13.2K watts
50mm 11.2 volt drop at 75 amps/ 18K watts

I was planning on feeding the from the supply into a switchfuse then a CU and earth rod at the shed end?

thanks in advance

 

[Guest55]

why are you looking at cables that give you a 11v voltdrop ?

it needs to be below 6v volt just for your lighting anyway ?

cant do the calcs for you without an Ib , but i would imagine the cable will be no less than 95mm even for a smallish load.

anyone who can afford the land and to build stables on it can pay for it to be done properly , end of.

 

[FCC5206]

Sorry unless im being a numpty 5% voltdrop allowed for power at 240V thats 11.5 volts and the amps watts ive calculated with would be the max load permitted that falls within the 5%.
I would have thought you have to calculate power as its a shed supply so will be both and thats the worse case.

Am i way off then?

 

[GLENNSPARK]

why are you looking at cables that give you a 11v voltdrop ?

it needs to be below 6v volt just for your lighting anyway ?

Cant do the calcs for you without an ib , but i would imagine the cable will be no less than 95mm even for a smallish load.

Anyone who can afford the land and to build stables on it can pay for it to be done properly , end of.

6.9v....

 

[Guest55]

6.9v....

......at the final light point
which means it will have to be less than 6v at the db to have any chance of achieving this.
;-)

 

[Guest55]

Sorry unless im being a numpty 5% voltdrop allowed for power at 240V thats 11.5 volts and the amps watts ive calculated with would be the max load permitted that falls within the 5%.
I would have thought you have to calculate power as its a shed supply so will be both and thats the worse case.

Am i way off then?

so there are no lights in the stable ?
you need to achieve no more than 6.9v volt drop all the way from the dno cut-out to the furthest light in the stable.

 

[Darkwood]

@FCC5206.... Gonna have to be a bit blunt here but dont take it as a dig.

Reading through im aware your customer is not forthcoming with info but you have been told its a 2bed house to design for so rather then throwing random 100amp figures out there try be more realistic and lets say an 18KVA supply would be adequate for your average 2up 2down.

You expect to run this off an existing house which may have a DNO fuse as low as 40amp that we can't know without enquiry and can't thus understand why such a large supply is been thrown in unless it can be confirmed the house could have a larger supply fitted at a future date. Has anyone even discussed an upgrade as well as existing fuse size with the DNO?

If the possibility of running this cable is an option for future plans then also to think about is metering as it will be on the first property and if planning permission is given then building a 2 bed house will always be tagged to house one, its unlikely the DNO will adopt your cables you have run to loop off house one and meter house 2 individually... this will be a big issue for a sale if that's the plans ever.

So before even putting calculation to paper firstly get all the relevant info to see if its practical or just a waste of money putting this larger cable in. Your customer is the ill educated one and irrespective of there demands and preferences if you present the case that this is throwing money away you will gain a lot of respect and a good name.

Apologies if ive missed info already supplied so ignore any comment if the case but i got brain mash with all the street lighting trolling crap :banghead:

Edit to note here is the possibility that if house is built that heating maybe electric as i assume no gas exists down there either and will have to be put in at great cost.

 

[FCC5206]

@FCC5206.... Gonna have to be a bit blunt here but dont take it as a dig.

Reading through im aware your customer is not forthcoming with info but you have been told its a 2bed house to design for so rather then throwing random 100amp figures out there try be more realistic and lets say an 18KVA supply would be adequate for your average 2up 2down.

You expect to run this off an existing house which may have a DNO fuse as low as 40amp that we can't know without enquiry and can't thus understand why such a large supply is been thrown in unless it can be confirmed the house could have a larger supply fitted at a future date. Has anyone even discussed an upgrade as well as existing fuse size with the DNO?

If the possibility of running this cable is an option for future plans then also to think about is metering as it will be on the first property and if planning permission is given then building a 2 bed house will always be tagged to house one, its unlikely the DNO will adopt your cables you have run to loop off house one and meter house 2 individually... this will be a big issue for a sale if that's the plans ever.

So before even putting calculation to paper firstly get all the relevant info to see if its practical or just a waste of money putting this larger cable in. Your customer is the ill educated one and irrespective of there demands and preferences if you present the case that this is throwing money away you will gain a lot of respect and a good name.

Apologies if ive missed info already supplied so ignore any comment if the case but i got brain mash with all the street lighting trolling crap :banghead:

Edit to note here is the possibility that if house is built that heating maybe electric as i assume no gas exists down there either and will have to be put in at great cost.

Hi not taking as a dig so no worries it is a 100A PME supply and I totally understand the complecation with the whole 2 bed comment which is why i told him it couldnt be done as for what he wants that was why i was doing the calculations giving him options.
I would rather he knew what he was dealing with so he doesnt get some --- throw in a 10mm off his existing CU.
I know lighting will be in there been a long day could have just pointed out that its 3%!!

re doing them
a 35mm would only get about 7.2 KW and a 50mm 9.6 KW (both falling within the allowed 3% volt drop at 6.9volts thanks!!)

I really appreciate the advice and if I went to work on my horse everyday I wouldnt be on here trying to learn. there is more knowlege on here than i have so was attempting to prove to my costomer what he requires isnt on the cards!!

 

[Guest55]

youre looking at this the wrong way...
theres no point thinking along the lines of 35mm for 7.2kw , 50mm for 9.6 etc etc.
the real questions that need answering have nothing to do with cable calc and volt drop..........
what does the customer want to achieve ?
what are his budget limitations ?
is he aware of the realistic costs involved and design criteria that need to be met ?
factoring in spare capacity for the cable in the off chance he may want to expand in the future will add massive initial materials costs , does he want this ?

unless he can answer all of these questions convincingly then i wouldnt spend any time designing a submains for someone who just wants a cheap bodge.

 

[FCC5206]

youre looking at this the wrong way...
theres no point thinking along the lines of 35mm for 7.2kw , 50mm for 9.6 etc etc.
the real questions that need answering have nothing to do with cable calc and volt drop..........
what does the customer want to achieve ?
what are his budget limitations ?
is he aware of the realistic costs involved and design criteria that need to be met ?
factoring in spare capacity for the cable in the off chance he may want to expand in the future will add massive initial materials costs , does he want this ?

unless he can answer all of these questions convincingly then i wouldnt spend any time designing a submains for someone who just wants a cheap bodge.

Thanks biff55 I'm seeing him tomorrow with all the info I have and rough prices for cable etc. I can't see him being happy with what I'm going to tell him. It's not a job I really want to be putting my name to.