sub main to outbuilding

[belliezzz]

hi guys new to this so sorry if revisiting old stuff.

I need to run a sub main 200M from the service head to a log cabin
Super eco all LED etc, so 40A 9Kw max demand

if i use the cable calculators i get 185mm cable
we all know power networks cover huge distance with 35mm cable on 100A supply

I intend to use 2 core 25mm SWA bonding/earth the Armour at the origin then through a
60A double pole breaker terminating in an insulated enclosure with a 40A double pole breaker
then into a 17th board on a TT system

Your thoughts welcome on how i justify what i intend
any suggestions welcome

The fact that I'm part "P" & NICEIC means I'M authorized not that I'm any good

 

[Deleted member 9648]

According to my calculation 70mm swa will give you a volt drop of 5.5 v at the cabin @40a.
25mm will result in a volt drop of around 15v @40a. Wont comply with the 3% requirement for lighting will it?

How have you arrived at your maximum demand?

 

[Engineer54]

we all know power networks cover huge distance with 35mm cable on 100A supply

Think you'll find that the 35mm cable you are talking about are the short Tee's off the main distribution cable to service heads supplying domestic and small commercial properties. The smallest DNO distribution cables that i've personally seen, have been 4 core 95mm...

200 metres is a hell of a long distance. When sizing sub main cable you may want to think about using a parallel cabled sub main, could well work out cheaper too!! Hmm, ...Unless of course you start adding in a derating grouping factor into the equation!! lol!!

 

[D Skelton]

I will refrain from stating the obvious regarding your apathetic approach to the job and your obvious lack of knowledge, but I will say this and only this;

The voltage drop on a 25mm cable over 200m with a 40A demand will be a non issue if you are able to check the exact voltage tolerance of every single item of equipment to be installed and it can cope with less than the nominal (200-260V for example). Is this likely to be the case? No. But unless you do something, your install won't comply with the regs. I'd start with diversity!

 

[uksparks]

200m of 35mm, I hope you are getting it delivered as that's a fair amount of cable.

Excuse my if ignorance but will this not need joining too as its quite long, can you get a 200m length of that?

 

[shanky887614]

200m of 35mm, I hope you are getting it delivered as that's a fair amount of cable.

Excuse my if ignorance but will this not need joining too as its quite long, can you get a 200m length of that?

Yeah you can but you aint lifting that drum by hand, will be very,very heavy

Spec for 4c 35mm 200m is 500kg cable weight!!!

Drum will add a bit as well

 

[belliezzz]

unless you are rural , my farm house is supplied (admittedly concentric cable) 650m from the transformer

 

[jackhammerJIM]

Excuse my if ignorance but will this not need joining too as its quite long, can you get a 200m length of that?

:90:

pretty much any length you want uksparks

 

[jackhammerJIM]

The fact that I'm part "P" & NICEIC means I'M authorized not that I'm any good

Is this a company motto ?

 

[belliezzz]

the first thing to say is that i took the job over and the supply was to come from a closer house
BUT that house has a 60A supply a hot tub and a 9.5Kw power shower and it is tenanted, the farm owner has an 80A supply to a barn 200m away. the DNO have quoted 105,000 to put in a new 100A supply,
Max demand
i have now decided to wire the dish washer and the washing machine through a 2 way switch so the cannot be used together.
wash machine 3 kw
40 of the 65 dimmerble led down lighters 400W
5 kw of everything else (boiler audio visual kettle and microwave)
as all of the lighting is dimmerble and therfore quite happy to run at reduced voltage
so i can use the 5% as a genral circuit
also the mesured voltage is 237@the service head

 

[belliezzz]

Is this a company motto ?

No my moto is im friendly im polite and im cheep **** but cheep but you cant have everthing in life

 

[Engineer54]

unless you are rural , my farm house is supplied (admittedly concentric cable) 650m from the transformer

And what sort of voltages are you reading at the service head for no load and on load (during a time of typical max usage) after that 650 metres??

 

[Hawkmoon]

Think you'll find that the 35mm cable you are talking about are the short Tee's off the main distribution cable to service heads supplying domestic and small commercial properties. The smallest DNO distribution cables that i've personally seen, have been 4 core 95mm...

200 metres is a hell of a long distance. When sizing sub main cable you may want to think about using a parallel cabled sub main, could well work out cheaper too!! Hmm, ...Unless of course you start adding in a derating grouping factor into the equation!! lol!!

Agreed - App 10-2 'apply grouping factors only when it's not too pricey'!

Just kidding Eng - really not going there again lol

 

[uksparks]

:90:

pretty much any length you want uksparks

I have never tried buying cable that long, presumably you need to go to more of a specialist supplier if you won't a few hundred meters uncut?

 

[shanky887614]

I have never tried buying cable that long, presumably you need to go to more of a specialist supplier if you won't a few hundred meters uncut?

Just ask wholesalers, they will ring there suppliers and get it delivered to site.

If not there are places online that will

 

[Engineer54]

Just ask wholesalers, they will ring there suppliers and get it delivered to site.

If not there are places online that will

Trouble is, he hasn't got a clue as yet, as to what size cable to order!!

No problem having in-line joints in a cable(s), standard practice on longer runs. So long as the cable and joints and have been accurately position marked on a appropriate drawing.... Oh, and that the joints have been made off correctly obviously...lol!!

 

[jackhammerJIM]

I have never tried buying cable that long, presumably you need to go to more of a specialist supplier if you won't a few hundred meters uncut?

go direct to manufacturer uksparks

 

[belliezzz]

And what sort of voltages are you reading at the service head for no load and on load (during a time of typical max usage) after that 650 metres??

round the 200 when the night stores kick in im just making the point DNO have difrent ruels to us

 

[Engineer54]

round the 200 when the night stores kick in im just making the point DNO have difrent ruels to us

Yes the DNO's do have different rules, unfortunately you have to comply with BS7671!!

Depending on the cable size, supplying your house, i'd be very much surprised if you are seeing 200 Volts after 650 metres. And even if it were 200 V, i'd be complaining like hell to the local DNO!! lol!!