Yes ELVs <50Vdc.  IMHO its sheer madness to be involved with MV dc Panel strings - way too dangerous  IMHO in a domestic environment, and we dont have the skilled tradesmen to recognise this type of micro grid nor is there a recognised route to upgrade to this unfamiliar but hazardous system.  Way too many unschooled wannabees playing with fireworks.  It is utter negligence by our Political leaders to allow this to continue.  They only woke up to the hazards of amateur plumbers who didnt understand flammable atmospheres till a few houses were blown up flattened.  Then British gas had to step in a institute proper training courses with local tech colleges.  Where do our Electricians get proper upgrades?  A one man jobber cant afford an apprentice (with all the paperwork and oversight involved). He will only have a family member or friend involved.

Indeed - hence the point about enclosure/ containment. There is a tendency among those who have not seen it for real to think that ELV quite is safe to have exposed terminals - and it may well be safe from a shock perspective, and in more traditional cases where the fault current is limited such as bell transformers and dry batteries.

With all but the smallest lead-acid or Lithium-ion and similar the impedance can be very low, and there is no such protection, and the effect of a spanner or strap of a wristwatch causing a fault path to the wrong place  however can be devastating, forming that accidental welder without the current control.The burns on a finger from a briefly red hot wedding ring are pretty unpalatable as well. I've not done it but I have seen the pictures.

Even in a pocket 'vape' the current in the heater coil can exceed 20A from a lithium cell that is only a few CM3 in volume . Scale  to something the volume of a small fridge and the potential energy is pretty impressive very quickly.

The headline has to be - with battery banks, shock is not the only risk, and 'just' ELV wiring needs increasing respect the more current is available .

Mike.

Well said Mike, but out governing Powers and indeed the technical training organisation and their learned bodies have largely ignored this emergent electrical area (even though the hazards are well understood for a century in such industries as electric traction, electroplating, telephone exchanges etc).  No young engineers or electricians receive any specific instruction in the nature of ELV dc distribution.  Its left to old timers like myself who came up through industry and formal education to recognise this drastic gap in training.  When I was tasked with the recruitment "milk round" , I was very disappointed at the poor quality of graduate training for Electrical Engineers who were expected to go on to become system designers.  IMHO they would need a full 5 years alongside an experienced site engineer just to get a proper grasp of the subject.  We don't have such mentors available any more and plant electricians don't have time or patience to carry students along (neither generally are electricians funded and trained to give such assistance BTW).

So that leaves the naive public at the mercy of "Chancers" and "Cowboys" I am sorry to say  (bit like the Roofer trade)

IMHO we will fall victim to Politico whims and grandstanding as has happened with " promotion of Diesel vs Petrol cars", Electric vehicles (2nd values plummeted ,  Heat pumps, HS2 rail (never once was the concept of modern VIP style coaches with exclusive use of the motorway outer lane considered), Solar farms occupying arable farmland),  pursuit of Nuclear power stations 20years to build 10x original budget using very old outdated technology still producing environmental nightmare waste (see https://www.rolls-royce.com/innovation/novel-nuclear/micro-reactor.aspx

but what do  kno

Surely this doesnt apply to ELV <50V systems? 

It's a general BS 7671 requirement, so I believe it does. I suspect the thinking behind the regulation is to control the risk of overheating and/or fire from an overheating joint (as ever, compared with an unbroken conductor, joints are a source of weakness) and as that's related to current rather than voltage it doesn't seem unreasonable that it does apply to ELV systems as well (where if anything currents tend to be much larger). Individual product standards may well allow such methods, but usually only in specific circumstances where mitigating factors usually apply.

No young engineers or electricians receive any specific instruction in the nature of ELV dc distribution.

Someone must be getting some training - since ELV distribution has been used not only in the areas you mention but in some IT data centres too - where 48V DC distribution is sometimes used. 12V in caravans too (again with the potential for kA fault currents). I'd agree it's not trickled down to your typical domestic installer - but that's because there's little need for it at the moment - almost all commercial systems convert back to 230V a.c. and use the building's existing a.c. distribution system.

   -  Andy.

I have got to wonder what your agenda is here.  Are you seriously saying that it requires years of training to wire a few solar panels in series without electrocuting yourself or burning the house down?

Solar power is now mainstream.  Houses all over the country are covered in solar panels. They work, and it's very rare that anything bad happens.

I get the impression that you're trying to impose rules to make all larger-scale solar installations so impractical that nobody wants to install them.  Then having done that, you can clain that they were just a green fad.

Agenda!!!!!!!!!!!!  I am crying out for amateurs to get themselves properly educated instead of the painful "suck it and see" attempts shown on youtube by technically illiterate bluffers pumping out dangerous practices for the credulous public to play with.  Its as bad as showing kids how to make fireworks.   Perhaps you havent browsed enough of these crass vids to see how misleading and dangerous they are.

Maybe just sit back and let the inevitable tragic accidents occur 

Rob Tes said:

More homework needed here old chap. FYI you cant sustain an arc flash at 12 V.

Indeed ... although I think we know enough already. It's possible to cause an arc at 12 V DC (not AC) from two conductors in direct contact (we know this from car batteries) ... although it does "blow itself out" as the gap increases as the conductors melt.

Things can get interesting, though, with "constant current source" behaviour of solar panels and power converters.

We are talking "arc" and not "arc flash" here, and I would agree 100 % that we don't start to get too many problems with arc flash at 12 V DC, perhaps up to 24 V DC.

Rob Tes said:

No young engineers or electricians receive any specific instruction in the nature of ELV dc distribution

More accurately, I believe it depends where you've been employed in industry. Power supply to controls and telecoms (and 'telecontrol') never went away from ELV DC ! However, I agree in general, when we talk about "electricians" the industry moved away from DC in the 1960s, but it's coming back now !

Rob Tes said:

Agenda!!!!!!!!!!!!  I am crying out for amateurs to get themselves properly educated instead of the painful "suck it and see" attempts shown on youtube by technically illiterate bluffers pumping out dangerous practices for the credulous public to play with.  Its as bad as showing kids how to make fireworks.   Perhaps you havent browsed enough of these crass vids to see how misleading and dangerous they are.

Maybe just sit back and let the inevitable tragic accidents occur 

I wouldn't just limit to amateurs.

Simon Barker said:

Solar power is now mainstream.  Houses all over the country are covered in solar panels.

Yes, and DC battery storage is happening quickly too.

Simon Barker said:

They work, and it's very rare that anything bad happens.

I would be a little more cautious here, especially given some insurance companies' views aired in the past 12-18 months. But I would accept that's not "DC power cable fire risk" alone ...

Once again I find myself at odds... as a kid who actually did make fireworks, and indeed in the 6th form we made gun-cotton, sufficiently well to damage the greenhouse of the parents of one of my friends, there is a lot to be said for learning by doing.

We also got up to a lot of stuff that nowadays would be more than just frowned upon, but we also learnt a lot very fast and remained largely intact, and the one who did not was due to a moped accident.

To my mind the error  of modern society is to infantalise the 'consumer' and assume they are incapable of understanding and making any technical decision as if consumers are some blobby mass incapable of doing  anything more complex than signing a cheque,.

Some may be , but the rest really should have access the resources,  to find out how to do things well, and then allowed to either  get on with it themselves or to instruct an installed to do what they want. (I'm the sort of customer who comes at the tradesman when he arrives every morning to make sure that what he intends to do today matches my plan, not the other way round . )

The alternative is a sort  of societal brain rot. This I see it in many places,  folk in their 20s who cannot change the wheel on their car - fine if you live inside the M25 so you are within 20 mins of an AA truck and in an area of good phone coverage, terrible if you are on hols in the Scottish highlands,.. teenagers who do not know how to catch a bus, adults who cannot read a map.

I do not care if folk learn in a formal setting in a classroom or by the more traditional watch one do one teach one. but they do need to learn

Mike

mapj1 said:

To my mind the error  of modern society is to infantalise the 'consumer' and assume they are incapable of understanding and making any technical decision as if consumers are some blobby mass incapable of doing  anything more complex than signing a cheque,.

Not sure what that has to do with what we're talking about?

For example, is it OK to put gg type fuseholders in accessible places on battery storage systems in homes that can be simply "pulled on load" by anyone ... including children? Similarly, sitting series/parallel monoblocs without internal overcurrent protection on the floor (for example in the garage or even on boards in the loft)??

Because that's what's happening in some ("not amateur") installs?

mapj1 said:

To my mind the error  of modern society is to infantalise the 'consumer' and assume they are incapable of understanding and making any technical decision as if consumers are some blobby mass incapable of doing  anything more complex than signing a cheque,.

Not sure what that has to do with what we're talking about?

For example, is it OK to put gg type fuseholders in accessible places on battery storage systems in homes that can be simply "pulled on load" by anyone ... including children? Similarly, sitting series/parallel monoblocs without internal overcurrent protection on the floor (for example in the garage or even on boards in the loft)??

Because that's what's happening in some ("not amateur") installs?

And an educated customer or a customer who's friends felt able to offer an opinion would pick up on this and say 'that's not right' much as we all know helpful folk who will tell you that your car has a problem - even if as in  my case you already know.

Thus the wider educated collective can correct - being a far better policeman than some trade body that looks at a few jobs a year that are within a short drive and easy to look at, where a large part of their aim is to keep the subscription payment flowing.

Mike.

mapj1 said:

And an educated customer or a customer who's friends felt able to offer an opinion would pick up on this and say 'that's not right' much as we all know helpful folk who will tell you that your car has a problem - even if as in  my case you already know.

Thus the wider educated collective can correct

I do take that point in general. But that doesn't appear to be happening with Solar & Battery installations.

I agree it isn't but then where is the public information on what to look for ?

That absent  public profile again - Rather like how to check your tyres or oil, how to see if your electrics look dicky... It would not be hard. Perhaps it is a pity the old scary safety film unit is no longer in operation...

(I did wonder if British Public information films of kids being hit by trains and tractors or being accidentally locked in fridges and other such stuff were a side effect of the film classification system being quite strict, so frustrated British horror film makers ended up doing things like The Apaches or The Finishing line instead where they could let rip in the name of education. What they could have done with an unprotected  DC supply I wonder ? )

Mike