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.

Rob Tes said:

Have you amortised the total cost of installation inc wiring switchgear inverter (fails in 5 years maybe) panels need replacing etc?  Batteries?

Panels should have a warranty of 20 - 25 years.  Inverters these days tend to come with a 10 warranty, or more.  I assumed no battery.

Rob Tes said:

Surely this doesnt apply to ELV <50V systems? 

Just to clarify, most solar PV systems are not ELV. Typical operating voltages for small domestic systems are ~600-800Vdc, up to utility installations with open circuit voltages of 1500Vdc. Operating currents are of the order 10-20A, depending on configuration, obviously more if anything is in parallel (or if the modules are in reverse current due to mismatch or fault)

It is also worth noting that solar PV installations rely on the measure of double or reinforced insulation, with class II equipment and insulation monitoring devices.

The conductors, at least for sections on the array itself, should be fine wire flexible (cl5) stranded tinned conductors under that insulation, in the most part because anything on the array will be subject to frequent thermal cycling and wind movement.

The connections will also be exposed to a wide range of temperatures (in the UK behind a panel could expect an ambient temperature from -15°C to +70°C with daily swings), are likely to see high degrees of moisture and are likely to be difficult to inspect. And yes noting the parallel thread on this topic I would expect similar in someone's loft.

Hence the use of connectors, and connections generally, made to a standard.

For domestic installations, anything >50vdc is way outside my comfort zone, but thats my personal prejudice .  Aside from shock hazard,  my concern is that switchgear/fusible links etc are notoriously suspect for circuit protection under load/fault interruption.  Properly authenticated circuit breakers (as per Siemens NF) are very expensive. The Main circuit breaker with AIC 5kA can be ca £1000 for the levels you are referring to.  I was astonished to see a well known US brand which supplies a complete solar kit down to the inverter mains outlet use a rotary cam switch (typically seen on electrical panels) as a circuit breaker between the panels and the Inverter  (no internal arc quench in that design).

At least with ELV systems you can keep the methods of last resort to hand on a shelf by the distribution board - namely a proper set of cable cutters, leather gloves, welder goggles and a plant mister bottle to spray water on an arc flash fire.  But I am old school as were fire buckets with sand.

I have the same fear of 3 phase power and wouldnt trust any old tradesman installing that system (at least it has full industrial design system credentials behind it so I would need a professional design practice to provide  detailed installation drgs and BOM. The tradesman installer has to follow the drg to the letter and not be left to fumble his own interpretations on the back of an envelope (Ive seen this approach)

IMHO the approach to Solar systems is very slap dash and careless, no site installation drgs, BOM, cable run iso

Maybe the sorry tales of fast track installations reported on various Forums has given me a jaundiced view (I hate Roofers)

Rob Tes said:

anything >50vdc is way outside my comfort zone

From experience, I'm more worried about DC current than DC voltage. Anything more than a few (<5) amperes at 12 V or more is enough to draw an arc, and 1-2 amperes is enough to sustain it. At 5 V DC, more current is needed ... but not too much to be honest.

Shock isn't the issue, fire, burns and arc flash can be problematic.

I can't disagree with some of the other points that you make.

gkenyon said:

Anything more than a few (<5) amperes at 12 V or more is enough to draw an arc, and 1-2 amperes is enough to sustain it

More homework needed here old chap. FYI you cant sustain an arc flash at 12 V. You will get a spark but you cant develop a sustained arc (at STP) below a certain voltage.  This is ca 20Vdc.  A welder will tell you that you can only weld with 2 car batteries 24Vdc or more  YT vids are there.

and anyone who has tried it will tell you that 3 car batteries strike up far better but to go easy anyway, as it does them no good at all. A few minutes non stop welding can heat the battery acid to a temperature that does irreversible damage. On the very rare occasion it is needed, I prefer to see the batteries put in a ditch or on the other side of something solid like  a vehicle, so if one does boil and vent, the scope for injury is limited, and not all on-line videos show sensible behaviour - but that is not just about welding.
It is quite a good thing to know how to do however.

Mike.

However far more important is how to relate available energy, or rather rate of delivery, into a safe arc radius to avoid instant sun-tan or worse being basted with molten metal, and then to either limit access for body parts, or the energy available during fault, so that the two never coincide. By the time you are talking about needing buckets of sand, if you are in earnest, you are already on the wrong side of a how to design things safely.

M.

(Who is very much not afraid of 3 phases either 400 or 690, when properly fused and in suitable containment, or indeed higher voltages too, but with rather more caveats. )

mapj1 said:

when properly fused and in suitable containment, or indeed higher voltages too, but with rather more caveats. )

Anyone understand this?

Gone OT here

I wasnt discussing using car batteries for regular welding, simply giving an example to show that you need a minimum voltage to sustain a dc arc, 12Vdc is not enough, 24Vdc will do it.

The real danger to health from an arc blast is the molten droplets of copper becoming instantly vapourised and expanding with explosive force ca 70,000 times expansion.  You dont want that in your face, nor the huge blast of UV and eye damage.  Its why copper fuse wire is encased in a ceramic tube and HRC fuses have sand added as well to quench the arc.  Look up YT and see some examples of fuse rupturing fault currents.

Fuses are given  an AIC or Amperage Interrupt Capability is the maximum fault current that the protective device is able to clear safely without causing damage to equipment or personnel or welding closed.

This can be 5-20kA 20,000 Amps! typically (or much larger for HV).  Plenty of room to study here to really understand the risks as I have this past year and is the reason for my OP.  Electricians are not traditionally trained in this specialised area of LV dc high current systems. 

Even something as elementary as making ring terminal bolted joints can go badly wrong (as per busbars in battery banks).  If you use a Flir IR camera it will be surprising to see where significant hotspots are developing within those bulky cables under full load.  Those hot spots over time can develop tiny arcs that grow seriously.  viz YT

Off gridders know about this.

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

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

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:

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?

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