Single phase vs 3 phase elecy

[Mike_scotland]

Hi,

 

We have a plot in the country the plot is in the middle of 2 cottages and there is overhead electric poles running along the road also adjacent to the plot, my question is do you think rural areas will have 3 phase electricity possibility? 

 

If not can you comfortably run air source pumps ,solar panels etc with single phase? 

 

We have been told it will be roughly 10k for electricity that is taking it under a road and Into the plot. (Its proberly about 10m from pole to plot boundary)

[ProDave]

If it is overhead lines, if there are 2 cables it is single phase, if there are three,  then it's 3 phase.

 

Assuming a new build with a half decent amount of insulation a single phase supply is plenty to run an ASHP and all the other stuff you want.  e.g. our ASHP is rated at 5KW so will rarely draw more than about 2KW of electricity or about 8 amps.

 

There is probably only a compelling need for 3 phase if say you have some machine tools that need it, or you are likely to want a LOT of solar PV.  If you only have a normal amount of solar PV then splitting the house load between 3 phases makes it harder to self use all that you generate.

 

It cost us £1K for the electricity connection and £1K for the road crossing under a single track road, so your £10K sounds expensive, but it depends exactly what work is needed (e.g new transformer etc) Have you got an actual quote yet or is that figure hearsay?

[Onoff]

22 minutes ago, ProDave said:

There is probably only a compelling need for 3 phase if say you have some machine tools that need it, or you are likely to want a LOT of solar PV.

 

Worth having a 3P connection for a (future) super fast EV charger?

[Mike_scotland]

Description of proposed works and assumptions Proposal: SSEN to carry out a pole termination onto LV pole 8 Replace pole 8 with a new intermediate pole and install a stay – ** this may not be required ** From pole termination, lay approximately 30m of 3c95mm² Wavecon cable to across the road. Pot end mains cable and carry out a single phase service joint. From service joint lay no more than 20m of single service cable to the meter position. Customer is to arrange entire cable track excavations and reinstatements at no additional cost to SSEN. If a formal quotation is requested in the future and it proves that we require more than this amount of cable, it would incur extra costs

 

This is what is on the letter I recieved for a online rough budget. So I'm hoping it's slightly lower.

 

It was 4-5k for the above^^ 

 

Then 2500 for excavation and reinstatement of road it's a out 5 metres.... then 1500 for permit to close and dig the road.

 

Thanks for the additional info makes me feels better now we can use a single phase.

[joth]

55 minutes ago, ProDave said:

If you only have a normal amount of solar PV then splitting the house load between 3 phases makes it harder to self use all that you generate

Might be true for commercial users, but for domestic 3phase there's no requirement to balance phases and you're billed based on the instantaneous use (or export) netted across the phases, so there's no penalty for splitting generation or consumption across phases. This is codified in Part C of the SMETS V2 spec. 

Snag: no one makes a polyphase SMETS meter, but the existing non-smart alternatives are supposed to bill the same way.

 

Anyway I agree you're unlikely to need 3phasr but stillI I'd get a quote it anyway and if the price difference is negligible do 3 phase.  you can always have your supplier fit a single phase meter initially, but will give future flexibility that's very expensive to retrofit.

Edited December 29, 2019 by joth

[Mike_scotland]

2 minutes ago, joth said:

Might be true for commercial users, but for domestic 3phase there's no requirement to balance phases and you're billed based on the instantaneous use (or export) netted across the phases, so there's no penalty for splitting generation or consumption across phases. This is codified in Part C of the SMETS V2 spec. 

Snag: no one makes a polyphase SMETS meter, but the existing non-smart alternatives are supposed to bill the same way.

 

I'd get a quote for installation of both single and three phase mains feed and if the price difference is negligible do 3 phase even if you only have your supplier fit a single phase meter initially, it will give future flexibility that's very expensive to retrofit.

I think there is only 1 phase as the surrounding electricity poles have 2 wires.

[Ed Davies]

48 minutes ago, ProDave said:

if there are three,  then it's 3 phase.

 

I think this could be misleading. Here's the transformer outside the kitchen window of the house I'm renting with the single-phase supply into the house. I think what's happening here is there's a single-phase 11 kV supply coming down the hill (tapped off 3-phase the other side of the main road). This is transformed down to LV (230 V) and put on those three wires going horizontally along the back of the small row of houses here. My supply then taps off the lower pair of those.

 

Given that the input is only single phase there can't, I don't think, be proper three phase on those three LV wires. I suspect it's a 230-0-230 V setup (i.e., two phases 180° apart). You could also label it, I imagine, L1-PEN-L2. I also assume the two blobs further down the pole, just above the line of the trees, are the isolators for each of those phases.

[ProDave]

You might look at other options for the road crossing.  You can get any contractor with a street works permit to make the road crossing, but when I enquired I could not find a contractor cheaper than SSE

 

The road opening permit is interesting.  I was told all the utilities have a permanent road opening permit, so don't have to apply for one for each job, which is one thing that is against a private contractor.

 

Before you make a decision, do you need any other services across the road?  In our case water, electricity and telephone had to cross the road, and in fact Scottish Water gave the cheapest price for the road crossing so they installed the water and made the road crossing first, and in the process we installed ducts for the telephone and electricity across the one road crossing.

[ProDave]

2 minutes ago, Ed Davies said:

 

I think this could be misleading. Here's the transformer outside the kitchen window of the house I'm renting with the single-phase supply into the house. I think what's happening here is there's a single-phase 11 kV supply coming down the hill (tapped off 3-phase the other side of the main road). This is transformed down to LV (230 V) and put on those three wires going horizontally along the back of the small row of houses here. My supply then taps off the lower pair of those.

 

Given that the input is only single phase there can't, I don't think, be proper three phase on those three LV wires. I suspect it's a 230-0-230 V setup (i.e., two phases 180° apart). You could also label it, I imagine, L1-PEN-L2. I also assume the two blobs further down the pole, just above the line of the trees, are the isolators for each of those phases.

That's an unusual case. It's a long time since I have seen individual cores for LV distribution on a pole like that.

 

That is indeed single phase 11KV at the top.

[Mike_scotland]

9 minutes ago, ProDave said:

You might look at other options for the road crossing.  You can get any contractor with a street works permit to make the road crossing, but when I enquired I could not find a contractor cheaper than SSE

 

The road opening permit is interesting.  I was told all the utilities have a permanent road opening permit, so don't have to apply for one for each job, which is one thing that is against a private contractor.

 

Before you make a decision, do you need any other services across the road?  In our case water, electricity and telephone had to cross the road, and in fact Scottish Water gave the cheapest price for the road crossing so they installed the water and made the road crossing first, and in the process we installed ducts for the telephone and electricity across the one road crossing.

Good point, the water is on the verge(my side) of the road so that shouldn't be a problem and I'm assuming the bt connection will be about there due too the fact the houses are  near by but I will check.

 

I am still at the planning stage(we have outline planning) but i would like to get water and electric into the plot asap.

[Mike_scotland]

This is the wire at the plot 2 cables. Will het better photo tomorrow, 

[ProDave]

1 minute ago, Mike_scotland said:

This is the wire at the plot 2 cables. Will het better photo tomorrow, 

A better picture would be interesting. The 2 cables appear to be different sizes?

 

A picture of where the wires join the poles in both directions might make it clearer.

[Mike_scotland]

2 minutes ago, ProDave said:

A better picture would be interesting. The 2 cables appear to be different sizes?

 

A picture of where the wires join the poles in both directions might make it clearer.

Its tough as on google maps there is 5 wires haha obviously from the past. But these photos are mine from a few weeks back during surveys etc.

[Mike_scotland]

6 minutes ago, ProDave said:

A better picture would be interesting. The 2 cables appear to be different sizes?

 

A picture of where the wires join the poles in both directions might make it clearer.

This is what I got from SSE.

[ProDave]

The top one is a multicore LV (230V) distribution, and the lower one is BT

 

Lets hope you are not stung for the cost of a new pole, it seems cheeky to possibly be charging you for that.

 

 

[Stewpot]

27 minutes ago, ProDave said:

In our case water, electricity and telephone had to cross the road, and in fact Scottish Water gave the cheapest price for the road crossing so they installed the water and made the road crossing first, and in the process we installed ducts for the telephone and electricity across the one road crossing.

 

That's interesting - they allowed you to install your own ducting in their trench, and the other utilities were happy to use it? Presumably different ducts for each utility. Did that mean Scottish Water had to dig deeper? How did you terminate the outside end of the duct?

 

On the original topic - an induction motor is better suited to three phase, and it will run more smoothly and I would guess more efficiently. If you have the option of machine tools, or plant with three phase motors, it might be a good option. I'm in the process of purchasing a plot which has three strands of cable going overhead (11kV, I presume), and the local farmer said that was because he wanted three phase, so I've assumed 3 wires = 3 phase and 2 wires = 1 phase.

[Mike_scotland]

5 minutes ago, Stewpot said:

 

That's interesting - they allowed you to install your own ducting in their trench, and the other utilities were happy to use it? Presumably different ducts for each utility. Did that mean Scottish Water had to dig deeper? How did you terminate the outside end of the duct?

 

On the original topic - an induction motor is better suited to three phase, and it will run more smoothly and I would guess more efficiently. If you have the option of machine tools, or plant with three phase motors, it might be a good option. I'm in the process of purchasing a plot which has three strands of cable going overhead (11kV, I presume), and the local farmer said that was because he wanted three phase, so I've assumed 3 wires = 3 phase and 2 wires = 1 phase.

I'm honestly not sure what to think as my electric only has one wire? But further much further down the road it has 3 wires so maybe my soon to be neighbours feed is taking off the 3 wires I really dont know or understand.

[ProDave]

4 minutes ago, Stewpot said:

 

That's interesting - they allowed you to install your own ducting in their trench, and the other utilities were happy to use it? Presumably different ducts for each utility. Did that mean Scottish Water had to dig deeper? How did you terminate the outside end of the duct?

 

 

Water is deepest at 900mm, so it was handy that SW gave the cheapest road crossing quote.

 

I installed a black duct for the electricity, all the way from the joint hole, to my meter box, with a draw string, so SSE just had to pull their cable through and terminate it.

 

I installed the grey duct and SWA phone cable that Open reach had supplied from the joint hole up into the house.

 

No complaints from anybody.

[Stewpot]

7 minutes ago, Mike_scotland said:

I'm honestly not sure what to think as my electric only has one wire? But further much further down the road it has 3 wires so maybe my soon to be neighbours feed is taking off the 3 wires I really dont know or understand.

 

I wonder if they can do single phase with 1 wire, using the ground as neutral as well as earth.

[ProDave]

8 minutes ago, Stewpot said:

 

I wonder if they can do single phase with 1 wire, using the ground as neutral as well as earth.

The incoming cable to the site will almost certainly be PME with the inner core as L and the outer as a combined N and Protective earth (PEN)

 

It will look like "1 wire" up on a pole.

[Onoff]

Like this maybe:

 

[Mike_scotland]

Aslong as I can run my ashp I'm happy haha

[JFDIY]

We've a right mix here, the overhead poles have 4 wires (3 phases + neuteal), then at the next pole it goes to a twisted 4-core cable serving the next farm after the 1/3 of a mile of cable was stolen.

 

My 3ph supply comes from the 4 separate conductors as a single concentric cable, so you just can't really tell unless you get a decent hight Res photo or have access to one of the ends.

 

Might be worth following the kind and asking the end users.

 

It only cost me £500 extra for 3ph so I'd always enquire about both costs, I had it for machine tools, but gives more flexibility in the future as mentioned above EV charging and solar generation to name a few.

[Jeremy Harris]

13 hours ago, JFDIY said:

We've a right mix here, the overhead poles have 4 wires (3 phases + neuteal), then at the next pole it goes to a twisted 4-core cable serving the next farm after the 1/3 of a mile of cable was stolen.

 

 

That;s most probably because the LV overhead network is being changed from the older separate conductor system to ABC, Aerial Bundled Cable, whenever a section needs replacement.  ABC is more reliable and cheaper/quicker to install than the old separate conductor system. 

 

As an aside, ABC is rather cleverly designed, as the outer sheathing of each of the bundled conductors is moulded with a number ridges to denote the phase, so 1 ridge = L1, 2 ridges = L2 etc.  The PEN has lots of ridges, around 12 IIRC.  This means that the people working on it can easily identify which conductor is which just by feeling the outside of it.