A little confused on SWA sizing for mains supply

[scottishjohn]

Ok 

trying to work out cheapest way to run 500 metres of supply to plot 

 I have not asked  supplier  yet for a quote 

but I have been told its 10k a pole--

as i have not got site tied up yet  do not want to make an official requests

so looking at big swa

now all the cable claculators i look at give me  the size --eg 300mmsq for 415v @200 amps @500 metres for the cable ,but when i go look at cables they don,t list them that way but at as conductor dia 

so when i do the calc  to get surface area it don,t match  up correctly 

do they add ALL the conductors together to get the surface area ,and why not just put booth measurements on the cable spec?eg 75mm dia (4 core) =370mm2,which was the closest way i could get them to match ,no allowing for losses in cable 

I,m even more confused as a sparkie said he worked it for me and the cable would be 40k 

i did the  costing numbers using a 95mm swa --biggest i could find and it came out at 14k

I am obviously missing a bit of  definitive info on how the equate conductor dia to the mm2 it says in the calculators

 

[Temp]

This was the first 300 sq mm cable I could Google with pricing..

https://quickbit.co.uk/300mm-4-core-swa-cable

 

£80 a meter * 500m = £40,000 

 

Ouch.

[Temp]

Most cables are sold by the area of each core not the diameter of the cores. It's just that sometimes they are lazy and drop the sq or ^2 in the description. Eg When they say a cable is 2.5mm they usually mean each core is 2.5 sq mm in area.

 

So I'm afraid if the calculator says you need a 300 sq mm (or just 300mm) cable I'm pretty sure it means "300 sq mm per core".

 

[ToughButterCup]

3 hours ago, Temp said:

[...]

It's just that sometimes they are lazy and drop the...

[...]

 

How often that happens ... ?

[PeterW]

This is why DNO don’t use SWA for power supplies - they use concentric. 

 

At 500m you are looking at  a fair cost whatever you do , but they tend to subsidise and in Scotland it’s also cheaper sometimes due to grants. 

 

Not sure why you want 200A supply though...?? May be cheaper with 2 x 100A supplies. 

[ProDave]

Definitely get a quote from the DNO. As above, they will use concentric cable so only 2 cores and the cost of that will be less than SWA of the same conductor area. The important thing is they can use it on their network, but you can't use it after the meter for your own supply.  But whoever supplies it, it will be a big cable.

 

Have a search of the forum, I am sure somewhere, someone found a grant scheme in Scotland that will cover part of the cost of a new supply.  Again that would not apply if you had the supply terminated some way away it would not cover the cost of your own cable.

 

The only comparison I have is a local near here had to have 2 poles worth of 11KV overhead line taken down and re routed underground around his plot.  That cost him about £10K.  So on your measure that's £5K per pole for 3 phase 11KV underground.  So a single phase 230V supply should be a lot less than "£5K per pole"

 

One way you might get the cost down, is do a thorough and accurate estimate of your actual electricity load and you might get away with a lower rating supply, e.g if you only asked for a 12KVA supply.

[Onoff]

https://sse.com/communities/communitytrust/

[scottishjohn]

the closest pole is a 3 phase one 

and to future proof the site ,as pv will be on the list at some stage ,

,and its a big site +house,so large PV array is easily doable 

architect is saying, as a guesstimate, at this stage  he would specify a 200amp supply .

 but yes maybe worth a "secret service " enquiry  at this point to dno about costing and sizes needed

 

 

[newhome]

34 minutes ago, ProDave said:

Have a search of the forum, I am sure somewhere, someone found a grant scheme in Scotland that will cover part of the cost of a new supply.

 

The great north / south divide ?. The scheme only covers the north of Scotland. Unfortunate for those in the south with huge connection costs. 

[Conor]

10 minutes ago, scottishjohn said:

the closest pole is a 3 phase one 

and to future proof the site ,as pv will be on the list at some stage ,

,and its a big site +house,so large PV array is easily doable 

architect is saying, as a guesstimate, at this stage  he would specify a 200amp supply .

 but yes maybe worth a "secret service " enquiry  at this point to dno about costing and sizes needed

 

 

 

First thing that came in to my head when I read your situation was "off-grid". The numbers you're talking would buy a hell of a lot of PV, storage and maybe backup generator/ wind/hydro.

[ProDave]

You won't get a 200A supply.  Your architect is not an electrician but if he designs you a house that is that poor it needs that much electricity (40KW) then sack him.

 

If you have a 3 phase pole to work from, then consider a 3 phase supply to the house.  A problem you might face being at the end of a long line is you might not get permission to install more than 16A per phase (3.68Kw) of solar PV.  Up to 16A you can just install it and notify the DNO, above 16A you need prior authorisation and that is not certain and may come with costs.  A 3 phase supply would let you install 16A per phase of PV or 11KW without having to seek permission.

 

I don't understand the cloak and daggers bit, you are obviously in discussion with the vendor, so just tell him you need to know the cost of an electricity connection and get SSE to give you a quote.

[scottishjohn]

If it works out  ,hen I can  give you details ,

you will understand why i want that  size supply  and yes 3 phase was always the plan 

i tried to talk to people regarding a supply  this morning ,but they need too much info  at this  time ,so we will wait till deal is done

and work  on 40k as cost for the time being .

I will have a 40ft high X 70m long banking that faces s/w  for PV if it all works out .

still needs to drop in price first  I think 

 

even at that going off grid don,t work out cheaper and a turbine will cost same anyway ,and take close to 20 years to pay back --if it don,t break down very often 

no hydro possible unfortunately.that would have been first choice

[ProDave]

I am intrigued to find out why you think you need such a big supply. 

[Temp]

200A at 220V/single phase might be reasonable if you want more than one electric shower and a car fast charger.

 

It works out less than 200A if you get 415V/three phase.

[scottishjohn]

1 hour ago, ProDave said:

I am intrigued to find out why you think you need such a big supply. 

I hope to be able to show you  at some point 

the thing i.m going for is not on open sale at this time 

and if it were i am pretty sure i would be blown out the water by some   one  with shed loads of money .

so we have to try to go slowly

[ProDave]

16 hours ago, Temp said:

200A at 220V/single phase might be reasonable if you want more than one electric shower and a car fast charger.

 

It works out less than 200A if you get 415V/three phase.

In practice most DNO's wont want to supply a 200A single phase supply without a very good reason.

 

Try finding a domestic CU rated at 200A or even a single phase meter rated at 200A.  Just not going to happen.

 

[Temp]

Yes sorry bad choice of words on my part. I meant if you just add up loads you can get to 200A but obviously it wouldn't really be sensible to install a 200A a single phase system. In addition 200A at 220V is equivalent to about 61A at 415V three phase (if I've done my sums right, perhaps someone can check).

 

[scottishjohn]

budget price has now been obtained from crown  Utilities

waiting for another from scottish power networks 

was not as far away as I thought  -130m  and asked for quote for 60kva 3phase,which includes transformer

budget cost --that could change , hte quote  is with me digging trenchs +cutting trees down  for the underground  cable etc

£26k+vat 

It gives me a clue at least 

[Carrerahill]

On 14/05/2019 at 08:26, scottishjohn said:

the closest pole is a 3 phase one 

and to future proof the site ,as pv will be on the list at some stage ,

,and its a big site +house,so large PV array is easily doable 

architect is saying, as a guesstimate, at this stage  he would specify a 200amp supply .

 but yes maybe worth a "secret service " enquiry  at this point to dno about costing and sizes needed

 

 

I love these "electrical engineer architects"...

 

Speak to DNO, if you end up generating so much electricity that you need to export over 100A then this cable is the least of your worries. 

Edited June 6, 2019 by Carrerahill

[scottishjohn]

the main thing is to have big enough cable  in at this time for anything later ,like maybe a few holiday cottages+a big pv array  -nothing for sure just trying cost worst case scenario 

 and not have up grade supply later  if it all works out 

 

[andyscotland]

Generally speaking, a 200A 3-phase supply is effectively 3 x 200A supplies - in other words caters for 600A of connected load.

 

If you have a possible peak load of about 200A, then you would install either a 63A (which is very slightly under) or 100A 3-phase supply. Your installation circuits would then be split over the three phases, aiming to get the loads fairly evenly spread. So for example:

• The PV array would be connected as a three-phase "appliance" - so 1/3rd of the panels connected to L1, etc.
• If you've a main house that'll be used fairly consistently and has some big loads (heating / cooling etc) then you might give it a 3-phase supply of its own and split the various circuits across the phases. This adds a bit of complexity / cost compared to a standard single-phase domestic install which is why you usually only see it in commercial.
• If you had e.g. 3 holiday cottages that were fairly similar you would probably just connect one to each phase. This is essentially how the utilities connect up standard domestic properties.

Note that on a properly-designed three-phase supply a lot of the current in the neutral is cancelled out - the electrical waves are all offset to each other, so one phase is high while another is low. Therefore the neutral still only needs to be the same size as the phase conductors, even though it's connected to all the loads.

 

At 130m you'll be primarily sizing cables for volt drop, from a quick look at the tables I think you'd be looking about 35 sqmm c.s.a. SWA for a 63A supply, or 50 sqmm c.s.a for 100A depending on install method etc. Though as above if the utility run it in they won't use SWA.

 

Might be more complex if you're going to be installing anything industrial / specialist (large motors etc).