# Self-Build - Boundary Box help...

#### christianbeccy

We're in the early stages of a self-build. We plan a 3ph connection, which will have to be to a Boundary Box at 35m from the base of the pole. This is still some way from the house, probably around 50m. Is this a concern?

There is a closer pole that is probably shortens the distance between the Boundary Box and the house to about 20m, but it's £2000 more to connect here.

Any help is appreciated.

Further away = much larger cable required and longer trench, both of which will cost more.
Nearer = smaller cheaper cable and shorter trench, but the connection cost is more.

All depends on the relative costs of the two options.

Further away = much larger cable required and longer trench, both of which will cost more.
Nearer = smaller cheaper cable and shorter trench, but the connection cost is more.

All depends on the relative costs of the two options.

OK great, but with cost aside is the longer run detrimental in any other way?

The DNO are permitted to supply at a voltage of between 207 and 253 volts, and your permitted 5% on power and 3% on lighting, so it is the lighting which is real limit. My calculator only goes to 16 mm² so at 100 amp so will not work it out but would guess looking at least at 25 mm² so for 5 core looking at £20 per meter so 35 m = £700 and 50 m = £1000 however may need to go to 35 mm² which means £25 per meter so £1250 so likely cheaper for you to run cable not DNO.

But although the likes of CEF may publish price of cable, in real terms it is negotiable, so not so easy to calculate. And not included price to dig trench.

OK great, but with cost aside is the longer run detrimental in any other way?
Not that I can think of - if properly designed, the longer the run, the larger the cable will one use so as to get the voltage drop (and 'wasted energy' cost) down to the same level, so it shouldn't make any difference, other than in terms of cost (of both cable and its installation).

Kind Regards, John

You will not pay for the wasted energy though as the meter is at your end of the cable.

You will not pay for the wasted energy though as the meter is at your end of the cable.
That's true - but, as far as 'the planet' is concerned, it is still a cost in terms of wasted energy (unless you can think of some benefit which derives from 'heating the soil').

In any event, consumers in general will ultimately pay (in £s) for un-metered energy wasted in the distribution network, since the price they pay for metered electricity will take into account the energy for which DNOs and suppliers pay which is 'expended' upstream of consumers' meters.

In any event, consumers in general will ultimately pay (in £s) for un-metered energy wasted in the distribution network, since the price they pay for metered electricity will take into account the energy for which DNOs and suppliers pay which is 'expended' upstream of consumers' meters.

I once saw a figure of 10 to 30% for the the overall network - Have you seen a different figure?

I once saw a figure of 10 to 30% for the the overall network - Have you seen a different figure?
One only has to look at the efficiency of the network transformers of 1% to 2% and the older versions may be nearer 5% to see some huge losses.

One only has to look at the efficiency of the network transformers of 1% to 2% and the older versions may be nearer 5% to see some huge losses.
I doo of course mean 99% to 98% and 95%.

One only has to look at the efficiency of the network transformers of 1% to 2% and the older versions may be nearer 5% to see some huge losses.

There is a lot more to the network, before the power gets to where it is used, than just the transformer and losses are additive.

I once saw a figure of 10 to 30% for the the overall network - Have you seen a different figure?
I don't recall having ever seen 'a figure'.

However, it's obvious that those who do the generating the electricity will expect to be paid for all the electricity that they generate and fee to the grid, regardless of whether that energy is put to useful use by an end-consumer or is dissipated ('wasted') somewhere between the generator and the end-consumer - and that cost "of everything generated" will be passed on by suppliers to the consumers.

My blind guess would be that an 'appreciable proportion' of the energy would not get to consumers, so I would not argue with the ballpark you mention - although I would probably have guessed nearer to 10% than 30%.

Kind Regards, John

although I would probably have guessed nearer to 10% than 30%.

It will of course vary with the load - transformers, up to a point, become more efficient as their load increases, where as cable efficiency is at maximum the lighter the load.

There is a lot more to the network, before the power gets to where it is used, than just the transformer and losses are additive.
Oh yes absolutely, again one only has to look at the wire strung up on pylons and although running at a tiny % of the current in an equivalent LV network the copper losses are very much still there.

Iassisted with installing KWh in the LV side of a customers HV network and within a few weeks they started questioning the difference of a 3-4% between the 'new meters' and the 'Suppliers meters', the Transformers were ancient.

Not that I can think of - if properly designed, the longer the run, the larger the cable will one use so as to get the voltage drop (and 'wasted energy' cost) down to the same level, so it shouldn't make any difference, other than in terms of cost (of both cable and its installation).

Kind Regards, John

That's the answer I was hoping for. Thanks!

#### DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Replies
17
Views
2K
Replies
4
Views
6K
Replies
4
Views
1K
Replies
8
Views
5K
Replies
37
Views
3K