Garage Electrical supply

I am in the process of purchasing a garage that whilst on the same street as my house is a few doors down, so there is no possibility of a direct connection to the existing supply. I have instead been investigating getting a new 100A single phase supply installed with separate meter, etc. but the quote has been much higher than expected (SSE ~6k). Seems their maps state the nearest electrical connection is the other side of the road and so it all needs digging up[1].
Anyway the real reason I am asking here is that in the garage next door to me there is, to my eye at least, what appears to be a suitable connection point (see dropbox link for image of this). It is currently supplying one flat next to the garage where the supply is housed. I think it should be possible to take another supply from this and feed it through the wall behind (This would be convenient as that wall is the party wall with my garage). So before I get back to SSE to point this out and push for them to quote on connecting here I was just wondering if others agree?
Thanks,
William
https://www.dropbox.com/s/uu934fk25yfcf3l/IMG_20170918_162520.jpg?dl=0
For those with limited vision or no access to the image:
Image shows a largeish (~1") cloth wrapped cable rising from the concrete garage floor into a large, roughly 30cm x 30cm, black plastic connection block mounted on a board, on the top of this to the right there is the standard black cable connection to the meter (for the flat) and what looks like extra holes in the middle and left, for possible further connections?
[1] As an aside I know I can get others to do some (most) of this work instead but won't they be working from the same maps and so come to the same conclusion and quote for the same?.
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Is the second terminal marked with a white or yellow dot?
If yellow, that looks like three phase, and you could presumably take a tap from the other phases, subject to regs about not mixing single phases in the same premises (which you probably won't fall foul of). You would presumably need the permission of whoever owns this garage.
If you want to piggyback on the existing single-phase connection, it's a question for the DNO whether it's thick enough to support another 100A (or whatever) on the same feed.
(Am I correct in understanding that it's wired in star form and the black is the neutral from the transformer? That suggests an additional tap would be yellow+black or red+black. Would that give the right 230V live-neutral?)
Theo
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On Monday, 18 September 2017 21:43:51 UTC+1, Theo wrote:

Surely 40A would do for a garage.
NT
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On 19/09/17 02:41, snipped-for-privacy@gmail.com wrote:

Agree 40A would be more than sufficient, but it wasn't given as an option when I enquired. I was asked about projected usage, but it seems that was just to determine single/three phase requirement, after I pointed out I really didn't need a three phase supply all the discussion was about a 100A single phase supply. I'm guessing it'd be cabled up for 100A regardless of the fuse they end up putting in.
William
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On 18/09/17 21:43, Theo wrote:

Thanks, the second terminal is indeed yellow, so I was hoping that a yellow+black or red+black for another feed would be acceptable, sounds like it should be. The owners of the garage are very happy for a connection to be made from this, and fed through the wall, but I guess there'll have to be some legal sign off. I hadn't thought about piggybacking on the existing supply but I guess it might be possible, perhaps more so if a 40A supply is an option. 100A is overkill for a garage, I just need to run a chest freezer and the occasional power tool, but the options I was given were 100A single phase or three phase.
William
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The connection work (and your own meter) would have to be done by National Grid, and therefore you need to understand what their policy was about sharing a three-phase box like that between two properties.
They'll want to make it 100amp so that in a few years time someone can charge their EV.
Everything else being equal, one question will be whether either of the two "spare" phases has enough extra capacity in your street (from the substation). If the phase with that spare capacity is Blue, it'll be a non-starter (because that cable will be potentially feeding 200A on just one phase).
And of course, I'd expect them to want to get a formal wayleave rather than just the informal agreement of whoever happens to live there this week.
--
Roland Perry

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Roland Perry wrote:

Not the DNO?
Chris
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Chris J Dixon Nottingham UK
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Possibly; the vans I see have "UK Power Networks" on the side, which maybe I'm mistakenly conflating with National Grid. If you'd asked me who my DNO was I'd have replied "Eastern Electricity".
--
Roland Perry

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On Monday, 18 September 2017 21:43:51 UTC+1, Theo wrote:

What is the problem with multiple phases in the same premises?
John
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the possibility of 415v shocks.
--
from KT24 in Surrey, England

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On Tue, 19 Sep 2017 08:43:24 +0100, charles wrote:

Indeed. SWMBO worked in a grammar school (quite an upmarket one) and had a sixth form 'computer lab' (she put in a Linux server and several clients).
She discovered that two adjacent power points on the PC desks were on different phases. Because I'd educated her well (!) she complained that at the very least they should be labelled. Nothing was done and *she* was labelled a troublemaker. She left not long afterwards.
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On Tuesday, 19 September 2017 09:54:58 UTC+1, Bob Eager wrote:

However, 3-phase power is sometimes installed in UK homes. I know of several. In many other countries it is commonplace. How much risk is there of simultaneously grabbing hold of two live wires at the same time? It is very hard to think of any way this could happen accidentally except perhaps if multiple phases are present in the same switch or connection box and alterations are being made on a live system.
John
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snipped-for-privacy@gmail.com wrote:

It's not just shocks, it's equipment damage.
Suppose you have a laptop and a powered USB hub plugged into adjacent sockets which happen to be on different phases. They're double insulated, hence no earth. There's a tiny bit of leakage to local ground on each one, not enough to trip the RCD. Suddenly there's 415v across the USB cable. If you touch both ends, you might get a belt. When you plug it in there may be a spark and it may zap something inside. While connections like Ethernet are magnetically isolated, USB is a direct electrical connection and is not expecting a 415v difference between signals.
Theo
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On Tuesday, 19 September 2017 11:20:42 UTC+1, Theo wrote:

For a voltage of 415V to be present between the USB connectors just before they make contact it would be necessary for all the leakage to come from one pole of each of the power supplies, which seems very unlikely.
Even if this did happen, the equipment should not care. USB ports have to cope with situations like a double-insulated USB hub being connected to an earthed computer. In this case, making the same assumption that all the leakage comes from one side of the mains they would still have to deal with 240V from the double insulated device to the earthed device. In CE-marked equipment the USB ports will have been tested with electrostatic discharges to the connector body of many kV. It is the connector body that makes first contact when USB connections are mated.
So whether the source voltage is 240V or 415V is really not going to make much difference when the devices are already protected against much higher voltages.
If you are holding both devices, you may get a small electric shock. However, the maximum shock current from double-insulated devices powered from different phases will be LESS than that from a single-phase powered device to an earthed device. This is because the voltage will be about 1.7x higher, but the leakage impedance will be doubled as there will be two sets of double-insulation in series with each other. So the worst-case 3-phase shock current will be about 0.85 times lower than single-phase to earth.
So why worry?
John
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[19 lines snipped]

I sympathise. BTDTGTTS.
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     snipped-for-privacy@gmail.com writes:

None.
The only requirement is that where 400V (two or three phases) is present and might not be expected, it must be labelled as 400V.
--
Andrew Gabriel
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On Sat, 23 Sep 2017 18:17:22 +0000, Andrew Gabriel wrote:

That's the 'Euro harmonised' phase to phase voltage. As lethal as makes no difference to the actual pre-harmonisation values of 415 (UK) and 380 (European) voltages within a couple of volts of the actual voltages in use.
--
Johnny B Good

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On 24/09/2017 02:19, Johnny B Good wrote:

No more lethal in real terms than the new "EU 230V" that most properties have if you follow the simple rules of proving dead before working on a circuit.
--
Adam

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If its on private property though, you would need written permission for your agent, ie the leccymob to enter and work on it, and of course it could mean a short interruption in supply. It also needs to be said that are you sure its up to the job of the extra load and do you know who owns the property its in? Brian
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