Anne Otis said:

Question  Is there  anything in regs preventing this ; Thought: The sockets must be somehow labelled / identified as alt supply  Any ideas to meet regs?

There may be issues with UK legislation (Regulation 21 of ESQCR) if there is no switching to completely disconnect the live conductors of the grid.

A floating supply or IT earthing arrangement is not recommended in general for domestic use in the UK. Also, Chapter 82 of BS 7671 requires the "backup" supply to be a switched alternative to the grid, not a "floating supply", so really it's not covered in the national wiring code in the UK. One key thing to remember is that, even if the manufacturer only provides one socket-outlet, the first thing users at home will do is connect multi-way extension leads to power equipment, some of which is connected into telecomms installations etc. - so what you thought was "floating" isn't any more.

See also the following in the IET Code of Practice for Electrical Energy Storage Systems Second Edition:

• Section 9.4 (and in particular 9.4.5 regarding limitation of use of IT system)
• Appendix F, item F1 (page 157)

I'm fairly sure the MCS standard for battery storage installations doesn't permit it either.

So, in summary whilst product standards, and to an extent installation standards, might appear to permit the use of a "floating backup supply", in practice in the UK for installations that are to be operated by ordinary persons as defined in BS 7671, we would strongly recommend the "floating backup socket" functionality is disabled when the inverter is installed, or, if power backup is required by the client, select an inverter that supports a TN-S earthing arrangement in island mode, along with switching that meets the requirements of BS 7671 and the legislation (Regulation 21 of ESQCR). Relays alone are not suitable for disconnecting from the grid in the UK - the switching device should provide isolation according to IEC 61140.

Dear all  Wish there was wat to thank everyone for contributing and I guess close this thread .  So hope this suffices:

Not familiar with solar electrics Was relying on a supplier but with me locally laying the groundwork  Now we have more constraints 

1.I stipulated would not tolerate a volatile lithium battery in my house  ( therefore would site inverter etc in garage at rear of my garden)

2.Proposed underground cabling . Supplier ( Victron kit)  refuses any guarantees if I do that 

3. Supplier now states I will need to supply separate earth electrode 

Not prepared to disfigure may garden with exposed wires nailed to fences , Mind boggles at some "Brunel tunnelling  for earth electrode  

Is it also most of you express disquiet  in one form or another Not all understood. 

So I give up : 

PS Still think the idea has great  meriit for smaller domestic affordable solar back up    Believe power starvation ix coming . I cannot see the merit of anything grid tie . Seems in USA back up generators are not novel. Though solar rather than petrol perhaps is.

With thanks to you all 

Ms O 

Anne Otis said:

PS Still think the idea has great  meriit for smaller domestic affordable solar back up 

The UK does permit "backup" ... but the right product needs to be selected. There are products on the market that can be installed in a conformant manner.

So I give up : 

That's a shame

.Proposed underground cabling . Supplier ( Victron kit)  refuses any guarantees if I do that 

That sounds peculiar - electrically underground cable isn't that different to say clipped to a fence.  I wonder if something has been lost in translation - or is the underground cable for the DC solar side?

3. Supplier now states I will need to supply separate earth electrode 

That bit makes sense at least.

Mind boggles at some "Brunel tunnelling  for earth electrode  

In most situations, hitting in a 4' long 3/8" diameter rod into the ground with a hammer suffices. Traditionally a few inches were left above ground to make the connection, but the preference these days is to sink it into a small pit with a lid over - still you're only talking about digging up less than 1 sq ft to a depth of a few inches - hardly IKB's territory and not a lot compared with digging the trench for an underground cable. (For my detached garage, which I wished to TT, I used one of the access chambers for the underground supply cable to house the electrode - two birds with one stone as it were)

 Seems in USA back up generators are not novel.

Not entirely unknown this side of the pond either - the subject comes up i the Forum fairly regularly. .Usually as a switched alternative though (so supplying all (or most) of the normal house wiring, rather than independent dedicated circuits) but it's all horses for courses. The entirely off-grid community has a presence here as well.

rather than petrol perhaps

Most true backup generators tend to be diesel rather than petrol - as petrol "goes off" after a relatively short time (in a matter of weeks or a few months, the lighter more volatile components of petrol evaporate, and the remainder doesn't work as well) - just as an aside.

   - Andy.

your local earth electrode will not be on the fence, just underground ;-) all you will have on the surface once it is all over is a small access cover at the top of the rod or rod. Neater than this one, it is about 15cm by 15cm the rod is 4ft (1.2m)long, and the diameter of your thumb,  and drives in just like a big nail. Just avoid the drains. and the gas pipe ...

. 

Oddly I have been looking at a battery and solar system something like this - a colleague at work keeps telling me how good it is...  And most of the companies I have spoken to have no problem putting the battery indoors, in the loft or indeed in an waterproof cupboard on the roof of my attached garage (!), so your suppliers sound like they may be more nervous than many. Cable underground in ducting is a perfectly sensible thing, and done all the time so again I am surprised.

That said all but one of the folk I have been talking to did  wither a bit when I start asking deeper questions about fault currents and Island modes, and I rather fear/ suspect many work by repeating the same recipe rather than a deep grasp of the design fundamentals.

(my own domestic electrics are a slightly non-standard shall we say... )

Mike.

your local earth electrode will not be on the fence, just underground ;-) all you will have on the surface once it is all over is a small access cover at the top of the rod or rod. Neater than this one, it is about 15cm by 15cm the rod is 4ft (1.2m)long, and the diameter of your thumb,  and drives in just like a big nail. Just avoid the drains. and the gas pipe ...

. 

Oddly I have been looking at a battery and solar system something like this - a colleague at work keeps telling me how good it is...  And most of the companies I have spoken to have no problem putting the battery indoors, in the loft or indeed in an waterproof cupboard on the roof of my attached garage (!), so your suppliers sound like they may be more nervous than many. Cable underground in ducting is a perfectly sensible thing, and done all the time so again I am surprised.

That said all but one of the folk I have been talking to did  wither a bit when I start asking deeper questions about fault currents and Island modes, and I rather fear/ suspect many work by repeating the same recipe rather than a deep grasp of the design fundamentals.

(my own domestic electrics are a slightly non-standard shall we say... )

Mike.