Cost of installing 3 phase vs moving existing mains head?

[joth]

Background:

1/ We need to move the existing 100A 1ph  mains head (currently location will become a downstairs shower, plus opportunity to address terrible airtighness of current main feed)

2/ We need to get G99 approval to hook up 8kW of PV generation (to give away the export for free, ?) which might be denied because it's only single phase...

3/ Moving to an all electric future, possible ASHP, car chargers, etc in future mean 3 phase might be just a useful thing to do anyway.

 

Anyone got any experience of typical costs, for:  a) moving the existing head (by about 5 meters; assuming we do all the labour and termination as far as we can) vs b) getting a new 3ph supply laid in from the street (about 20 meters away; again assuming we dig the trench etc)

 

Hmm as often the case, writing the question out it sounds obvious, but lets ask it anyway

 

(I shot ukpowernetworks an email to get ballpark indication, but no dice -- they just sent me forms to fill at length for a formal application.)

 

 

[Jeremy Harris]

It depends almost entirely on how far away the 3 phase supply is, plus whether it has enough capacity.  Sometimes you're lucky and there is a 3 phase cable nearby, other times you're unlucky and the nearest 3 phase cable maybe a couple of hundred metres away.  There aren't necessarily 3 phase supplies running down every road; here, for example, we have lots of single, or 2 phase, runs strung along the lanes in the village, with only a handful of 3 phase cables.

[ProDave]

As above. We are on a single phase 11KV overhead line and the nearest 3 phase line is over half a mile away so the cost of getting 3 phase here would be astronomical.  The only way you know is if you get a quote both for the move, and for a new 3 phase supply.

 

If you get the new supply, that is not oficially the end of it, you would still have to pay something to get the old supply removed or disconnected.  (I know someone who converted 2 houses into one. He refused to pay the £1000 to have the road dug up to disconnect the redundant feed, so it has been sat there for years, with noting but the electricity meter connected to the supply head on a zero standing charge tariff)

 

If you do get your 3 phase then you can connect 8KW of PV between 2 phases without needing prior permission.

[joth]

Our street is a relatively main-ish road with school a few doors down, so I'm relatively sure there would be something within a reasonable distance. It's all underground though (conservation area) so if there wasn't something nearby it would be an impossible job to run it to us.

 

 

So really in order to rule this whole idea out right now, I'm interested in the what the "best-case" (i.e. it is right at the end of our driveway) cost could be vs moving an existing head. If that's way more, then I can just save the effort on researching it any further.

 

Oh, and does a  3ph supply command a higher standing charge or anything?

 

[joth]

Answering my own question!

First. it turns out the cost estimate (with on site survey) was much faster than a G99 request. MUCH faster. Like, 3 days vs 12 weeks.

 

Costs for moving existing vs new :

a) moving existing single phase supply by 4 meters: aprx £1100

b) installing a new 3ph supply from the street (17m) and disconnecting the the old: £3900

 

Most of the costs in (b) is the fact they're digging up public carriageway (pavement only) so need permits, H&S, road signing, 3 crews, etc.

 

Other interestingly tidbits:

- we actually have a substation immediately on the boundary behind our  house. The surveyor's plans didn't show how it was connected to the main supply out front so he ignored that for costing

- the existing mains head could be moved to an "indoor" location because it's already indoors, and it's a renovation. For a rebuild, or for a brand new supply, the "new rules" kick in and the head+meter need to be outside the house.

 

I now have to decide if the future proofing benefits of a 3ph supply justify that hefty upfront cost. (It also de-risks some other parts of the build, namely moving supplies around inside and solar connection, but the cost is too high for derisking alone).

The fact we're going all-electric house does push us in favour of doing this. And enabling a 22kW car charger could be useful option in the future too.

 

Edited August 9, 2019 by joth

[patp]

Following with interest.