UK New electric supply connection

[wwilts]

New 46kVA electric supply to new backland dwelling (37m from footpath). Mains cable runs along the footpath at the road access.
Which option would you choose and why?

Option 1

Meter box near footpath. Own fuse and armoured cable (>30m distance) underground to new dwelling.

Option 2

Meter box 25 m from footpath. Own fuse and armoured cable (<15m distance) underground to new dwelling.

 

[Rockingit]

46kVA to a dwelling?? Are you sure you actually mean that?

 

[wwilts]

46kVA to a dwelling?? Are you sure you actually mean that?

Yes.
Two phase.
Future proofing for EV chargers.

Question: meter box near mains cable
OR
25m from mains cable (with SWA provided by DNO)

 

[Rockingit]

With respect, I think you need to take a second look at your demand calculations. Post up exactly what it is that you’re looking at building.

 

[wwilts]

With respect, I think you need to take a second look at your demand calculations. Post up exactly what it is that you’re looking at building.

One dwelling
with up to 2 EV chargers
22kW fast x 2
43-50kW rapid x 1

Charging point can be located near external meter box if needed to simplify cable to dwelling

Trying to understand pros and cons of external meter box located near mains cable OR nearer to dwelling

 

[westward10]

Yes.
Two phase.
Future proofing for EV chargers.

Question: meter box near mains cable
OR
25m from mains cable (with SWA provided by DNO)

You mean three phase?

 

[wwilts]

You mean three phase?

DNO states "dual phase supply installed into a secure waterproof cabinet provided and installed by customer"

 

[timhoward]

A simple sketch might be worth a thousand words with this one.

 

[Rockingit]

I'm assuming that you've already had the DNO quotation for the new transformer, etc etc?

 

[wwilts]

A simple sketch might be worth a thousand words with this one.

Here it is. Option 2 could have EV chargers near meter box.
From meter box to dwelling could be usual domestic supply (eg. 11 kVA)

 

[Rockingit]

In the meantime, to answer your question, you want to get the DNO intake and meter as close to the property as possible - the simple reason being that as/if/when something goes wrong it's the DNO's responsibility to fix it, not yours!! Remember - you only own from the meter onwards.

 

[Rockingit]

From your pic, I'd strongly suggest you just get the DNO to quote for a new supply to the property. And if you really DO want that much energy, I'd just ask to get a 100/3ph installed instead - may well be cheaper and will certainly be safer and easier to deal with on site.

 

[wwilts]

In the meantime, to answer your question, you want to get the DNO intake and meter as close to the property as possible - the simple reason being that as/if/when something goes wrong it's the DNO's responsibility to fix it, not yours!! Remember - you only own from the meter onwards.

Great. Understood, thanks

 

[brianmoooore]

You mean three phase?

If the DNO are talking two phase (230-0-230) then 3 phase may not be available. This has been a problem throughout most of my working area. Quite a few of my customers have two phase supplies, including myself, but I can count the number of customers I have with 3 phase supplies on the finger of my hands. Possibly just one hand.
In answer to the OPs question, definitely not option 1.

 

[telectrix]

agree with 3 phase option. you might want 3 phase equipment at some time in the future. and meter box as close to the dwelling as possible.

 

[pc1966]

I'm guess the two-phase is common in rural places when they just have twin HV cables to pull the supply off, and prefer to offer 230-0-230 at 100A rather than 230 at 200A for obvious reasons.

Usually I prefer the name "split phase" but it really is two phases as for a N-phase system each line is 360/N degrees different, and so when balance there is no neutral current.

The issue with single and 2 phase is you can't generate a rotating field or other phase sets from it, so motors need capacitors to get going and all of the sort of problem. In these days of VFD for motors it might be less of an issue, but there is still loads of industrial kit (and probably farming equipment) that assumes a 3 phase supply is present.

With 3-phase (or higher) you can use weird transformer arrangements to get any other phase arrangements you want, probably the most common has been the Scott-T to get 4-phase (as 2 * single phase at 90 deg to each other) or the ones using both star and delta windings, etc, for 6-phase supplies common for DC generation in the olden days of mercury arc rectifiers. Still probably used today, as it lowered the ripple on the DC supply (so less of a smoothing choke needed) and dropped the 3rd harmonic seen on the incoming HV side, but it has been years since I studied that sort of thing.

 

[telectrix]

agree with 3 phase option. you might want 3 phase equipment at some time in the future. and meter box as close to the dwelling as possible.

I'm guess the two-phase is common in rural places when they just have twin HV cables to pull the supply off, and prefer to offer 230-0-230 at 100A rather than 230 at 200A for obvious reasons.

Usually I prefer the name "split phase" but it really is two phases as for a N-phase system each line is 360/N degrees different, and so when balance there is no neutral current.

The issue with single and 2 phase is you can't generate a rotating field or other phase sets from it, so motors need capacitors to get going and all of the sort of problem. In these days of VFD for motors it might be less of an issue, but there is still loads of industrial kit (and probably farming equipment) that assumes a 3 phase supply is present.

With 3-phase (or higher) you can use weird transformer arrangements to get any other phase arrangements you want, probably the most common has been the Scott-T to get 4-phase (as 2 * single phase at 90 deg to each other) or the ones using both star and delta windings, etc, for 6-phase supplies common for DC generation in the olden days of mercury arc rectifiers. Still probably used today, as it lowered the ripple on the DC supply (so less of a smoothing choke needed) and dropped the 3rd harmonic seen on the incoming HV side, but it has been years since I studied that sort of thing.

think when i was at college, that part of studies clashed with a 2 week beer fest. no contest.

 

[brianmoooore]

It's commonly known as split phase around here, but technically it's two phase.

 

[plugsandsparks]

If it is 2 phase, might be worth re-visiting your EV charger options as the 22KW ones (AC) i know of are 3 phase and ditto for rapid chargers

 

[brianmoooore]

I'm guess the two-phase is common in rural places when they just have twin HV cables to pull the supply off and there is still loads of industrial kit (and probably farming equipment) that assumes a 3 phase supply present.

Tell me about it! I've spent many hours of my life trying to get suppliers to understand that I require equipment to be supplied with 480 volt single phase motors, not 440 volt motors.
It was common for them to deny such motors existed.

 

[wwilts]

If it is 2 phase, might be worth re-visiting your EV charger options as the 22KW ones (AC) i know of are 3 phase and ditto for rapid chargers

I was a bit confused by apparently differing messages following the DNO's quotation. The design states dual phase. The staff who then made a site visit to plan connection dates etc. said "3 phase". Perhaps it is 46kVA 3phase, for all I know (which is not much).

 

[plugsandsparks]

Post up the quote and we can advise

 

[wwilts]

Post up the quote and we can advise

It seems to be 100A 3p, just as you all advised. Apologies for the confusion.
Their drawing said "dual phase", but that is not in their detailed quote.
100A 3p it will be, I believe.

100A 3p 46kVA will suffice for EV charging, I imagine. For the dwelling itself (no heat pump / no AC), how many kVA would you allow?
And what underground cable would do from the meter box to the dwelling? T&E in duct or SWA? If SWA, 16mm2 or 25 mm2? 3 core?

Distance from meter box to dwelling<15m, of which <4m will pass under a driveway turning area.

 

[Rockingit]

100/3 is a ‘standard’ 3ph supply, you don’t really go downwards from that.

Why the fixation to have the meter separate from the dwelling?? Because, straight away in order to get 100/3 from an external point to the dwelling itself you’ve probably gained £1000+ of expensive and probably unnecessary works, and that’s before groundwork costs and hassle. You’d actually be downgrading your supply before you’d even used it for reasons to do with technical regs that I won’t go into here as I don’t want to confuse.

WWilts - if your user name is a reference to geography then drop me a private message, I may not be that far from you!

 

[JD6400]

New 46kVA electric supply to new backland dwelling (37m from footpath). Mains cable runs along the footpath at the road access.
Which option would you choose and why?

Option 1

Meter box near footpath. Own fuse and armoured cable (>30m distance) underground to new dwelling.

Option 2

Meter box 25 m from footpath. Own fuse and armoured cable (<15m distance) underground to new dwelling.

Normally I would say , get a quote from your DNO for their side of the work , for either option and then you will see if you have a larger enough price difference between the two in order to make it economically viable to do the majority of the work yourself. ( Saved one client £36k by doing this)
But now that you have shown your quote I would say that the DNO should the whole length , as it is not worth the pennies you'll save.

Also as you will see yourself if you follow the forum , Rockingit knows his stuff and you won't go far wrong with his help.
I am not trying to to put your knowledge down , but the fact you asked if running twin and earth in a duct was acceptable , to me would indicate you could do with some external paid help.

Good luck with your project

 

[wwilts]

100/3 is a ‘standard’ 3ph supply, you don’t really go downwards from that.

Why the fixation to have the meter separate from the dwelling?? Because, straight away in order to get 100/3 from an external point to the dwelling itself you’ve probably gained £1000+ of expensive and probably unnecessary works, and that’s before groundwork costs and hassle. You’d actually be downgrading your supply before you’d even used it for reasons to do with technical regs that I won’t go into here as I don’t want to confuse.

WWilts - if your user name is a reference to geography then drop me a private message, I may not be that far from you!

An electrician building their own house did this:
"a switch fuse in my meter box with an 80A fuse in it to discriminate from the suppliers 100A fuse. Meter In external kiosk. Can be connected and finished before the house is built so you have a site supply without having to move it later. No need for a meter box on the outside wall of your house. Run your own SWA able from this kiosk to the house when you are ready with no DNO involvement."

The new dwelling will come later, just trying to get supply to site. And to avoid unnecessary costs.
Will PM

 

[wwilts]

Normally I would say , get a quote from your DNO for their side of the work , for either option and then you will see if you have a larger enough price difference between the two in order to make it economically viable to do the majority of the work yourself. ( Saved one client £36k by doing this)
But now that you have shown your quote I would say that the DNO should the whole length , as it is not worth the pennies you'll save.

Also as you will see yourself if you follow the forum , Rockingit knows his stuff and you won't go far wrong with his help.
I am not trying to to put your knowledge down , but the fact you asked if running twin and earth in a duct was acceptable , to me would indicate you could do with some external paid help.

Good luck with your project

No pretence of knowledge here. Just trying to understand enough to make intelligent suggestions to builder.

 

[Strima]

I'd get 3ph all the way to the property then distribute from there.

 

[pc1966]

An electrician building their own house did this:
"a switch fuse in my meter box with an 80A fuse in it to discriminate from the suppliers 100A fuse.

You won't get meaningful selectivity between 80A and 100A as they are both subject to something like +/-10% tolerance, etc, and the total let-through I2t for the 80A clearing is less than the pre-arcing I2t of the 100A.

Typically you need to have a 1.6:1 ration for BS88 and other European fuses (i.e. two sizes, so 63A & 100A or 50A & 80A, etc) for that.

But really selectivity is only needed if you expect to need it. If you are putting in a switch-fuse for the long tails it is largely down to the regulations that require both a means of isolation (the switch) and OCPD that is matching the sub-main characteristics (i.e. 5s disconnect for fault in or at the end of the cable).

The regulations do allow the DNO fuse provided they agree to it being used. Realistically it is easier to fit a switched-fuse!

Where you need selectivity (and so fusing down a bit from the DNO) is when you have several circuits coming off the DNO fuse. And by that I mean several sub-mains, for example at a Ryefield board or where tails have been split to allow two CU or some massive load to be added and you reasonably expect a fault on one sub-main not to take out the lot.

For the typical case of long meter tails / sub-main you really ought to have it designed so that it won't be overloading the DNO supply anyway (diversity allowing) so having your own choice of fuse is down to it independently providing protection to your choice of cable and supply Ze, etc.

In that case you might be putting in 80A, even though on a hard fault it probably won't save the DNO fuse, because it then meets your 5s requirement and is enough for the planned loads.

 

[brianmoooore]

I've been involved with builds in the middle of nowhere on many occasions, and on some, I've got over the problem of a site supply by getting the builders to build just a small triangular section of the outer house wall to build the meter box into. I've then fixed my board (used on many sites) with an IP65 small RCD protected consumer unit and two IP55 double switch sockets on it, to the reverse side of the wall section, in what eventually will be the cavity.

 

[wwilts]

I've been involved with builds in the middle of nowhere on many occasions, and on some, I've got over the problem of a site supply by getting the builders to build just a small triangular section of the outer house wall to build the meter box into. I've then fixed my board (used on many sites) with an IP65 small RCD protected consumer unit and two IP55 double switch sockets on it, to the reverse side of the wall section, in what eventually will be the cavity.

Builder will need electricity before the building comes out of the ground. And DNO provides only 25 m of their own stuff within the quoted price. Suggestion was to provide external meter box/kiosk to receive DNO supply, & eventually run own SWA to dwelling. Then DNO does not need to provide another quote for covering the <15m distance remaining from kiosk to dwelling.

 

[Mikegh]

Won't 30m of swa give you less to play with on voltage drop and fault loop impedances in the building itself

 

[plugsandsparks]

BTW 100A Supply off three phase is around 70KVA so you can fill your boots with EV, lol
On a serious note, be aware of what charging the individual cars will take before blindly connecting 4 EVs and going to bed..??

 

[wwilts]

How about this approach:

Single phase supply to dwelling.
3 phase supply for EV charging only (as and when that is installed).

Workable?

 

[brianmoooore]

Won't 30m of swa give you less to play with on voltage drop and fault loop impedances in the building itself

It'll be the same voltage drop whether it's a DNO cable or a private one. The difference is that you won't have to take it into your calculations if it's DNO. Will help with loop impedance if it's TNC-S, not so for TNS

 

[Gavin John Hyde]

Just because you have a.22kw ev charger doesnt mean the car will charge at that rate. A lot wont charge above 7kw.
As.for DC rapid charging why have two 22kw if fitting one of these?
I installed.a.dc.rapid charger for a guy in Bath. Had to use a lifting machine to position it! Weighed nearly 100kg also had a.22 kw Andersen for visitors etc
He had a small fleet of cars for family, staff and security so needed rapid charging. When people.got back cars.were charged and cleaned.

 

[wwilts]

Just because you have a.22kw ev charger doesnt mean the car will charge at that rate. A lot wont charge above 7kw.

True. But in due course most cars might allow faster charging.
The 3 phase was obtained just to future proof the new build to some extent.

Does the distance from the 3 phase distribution board to the EV chargers matter much? For example, 3 m vs 20 m?

 

[Mikegh]

True. But in due course most cars might allow faster charging.
The 3 phase was obtained just to future proof the new build to some extent.

Does the distance from the 3 phase distribution board to the EV chargers matter much? For example, 3 m vs 20 m?

Costs more money ,.you.have to factor in the distance

About it I'd say

 

[Gavin John Hyde]

True. But in due course most cars might allow faster charging.
The 3 phase was obtained just to future proof the new build to some extent.

Does the distance from the 3 phase distribution board to the EV chargers matter much? For example, 3 m vs 20 m?

Yes, that extra 17M of cable will cost more anything from £50-£100 depending on cable, where purchased etc then you have cable fixings, larger glands. labour costs as trying to work with some large cables can be tiring and like wrestling an anaconda.
Then you have to account for voltage drop, 20M is a small run but when you are fitting a charger at a property and you have a cable run of around 40M then it becomes a much bigger issue, careful circuit design and calculation can mean you use a smaller cable and thus save money/materials. I had to get the groundworkers to run 10mm SWA 3 core recently for a garage install and whilst only supplying a single 7kw charger, some sockets and led strip lights, had to increase the cable size from 6mm to allow for the MD and voltage drop as the cable run was a right zig zag affair through rocky ground and around other services.