Solar Energy Systems installation UK - lack of skills

Rob Tes said:

Your reply and vid are out of context with my assertion  ie you are referring to a carbon arc system. 

I didn't specify that, and nor did you.

Once carbonisation takes place on the surface of other conductors, though, more prolong "sparking" and quasi-arcs can occur, but still perhaps not "arc flash" - I wouldn't, however, like to say it was never possible under any circumstances with 12 V DC systems.

Rob Tes said:

There are numerous vids with ca 100,000 followers showing how to meddle with Lion 18650 cells and rather trivialising the safety issue.

https://www.youtube.com/watch?v=CYBnEGYWgz4

How many  people just throw lion cylindrical cells in a drawer together (just like you might with spare zinc carbon cells)

I fully support you in this, and the other things you have said ... except perhaps I would recommend wearing eye protection even at 12 V DC.

In real installations, I have seen welded and vaporized components resulting from short-circuit faults in 12 V DC and 24 V DC systems (without carbon rods ) and for that reason, I would make the recommendation for at least some eye protection, especially where the prospective fault current is going to be more than a (very) few amperes..

AJJewsbury said:

A simple rotary isolator between PV panels and inverter is a pretty well accepted way of doing things. It's only intended as an off-load isolator to allow work on the inverter.

A lot of people dont understand the difference between an isolator switch and a circuit breaker.  Joe Public equates it with the light switch on a wall.

Your reply and vid are out of context with my assertion  ie you are referring to a carbon arc system.  My topic concerns fault currents in wiring/ protective devices etc using metal interfaces.  I am frustrated at deliberate attempts to dilute the issue of dc power system safety.  There is so much absurdly naive rubbish promoted on YT and giving untutored  Joe Public the idea of playing around with setting up his own solar system inside his house.   

There are numerous vids with ca 100,000 followers showing how to meddle with Lion 18650 cells and rather trivialising the safety issue.

https://www.youtube.com/watch?v=CYBnEGYWgz4

How many  people just throw lion cylindrical cells in a drawer together (just like you might with spare zinc carbon cells)

Have you seen vids of refuse lorries discharging their loads in the street because a lithium battery started a fire and produced smoke.

This is a regular occurrence in recycling centers

Would you let your kids experiment with lithium batteries?

When I am developing a project using Lions on my bench, I have the following kit to hand

A large steel cooking pot with lid containing a couple inches of sand at my feet

Wire/cable cutters to hand

Leather gloves and large tongs

Wear goggles over 12Vdc

Keep a plan water mister to hand to quench arc flash

Keep room exit clear in case of catastrophic event (room rapidly fills with highly toxic HF smoke)

How many of you understand the need for these precautions indoors?

That's more than sufficient current to draw an arc

Indeed, but nothing a d.c. circuit breaker towards the inverter end would do anything to help. I don't think we have DC AFDDs available yet (and no obvious place to position one in a PV string either). I guess it's back to the very old school methods - insulation, sheathing, maybe put +ve and -ve in separate conduits etc and keep some physical space between them(*) to manage the risks of parallel arcs.

* but not too far apart, we don't want a big loop, for EMI reasons.

   - Andy.

gkenyon said:

Yes, arc flash energy at 12 V may well be low,

and of course the arc flash is therefore not sustained for long enough for it to be what we know of as a "full blown flas" ... This particular point raises something very  interesting and important, in that if the voltage is sufficiently low, the model of "fault of negligible impedance" isn't always applicable ... the results are either:

• More risk of arcing at the "higher end of ELV" in DC systems - possibly risk of arc flash if there's sufficient current (although "sufficient" here may well be surprisingly low).
• More risk of a high resistance fault  at the "lower end of ELV" (say 30 V AC or DC, or less ... only a finger in the air) leading to fire - importantly, this is a possibility  with AC or DC. Having resistance in the fault may cause overcurrent protective devices to fail to operate.

Rob Tes said:

BUT  the sad thing here which my OP highlighted is that we dont have any formal training worth a damn to promote theis level of Safety Training

Agreed ... not everyone has the relevant training and experience.

Rob Tes said:

WRONG more homework needed GK

I think we are at odds only in terminology, and I have tried to explain that in a previous post. To sustain the arc is difficult with 12 V due to the very short distance necessary. Easier with carbon or carbonised metal ... I never said you can weld with 12 V using arc welding sticks ... but arcs can be drawn for short periods with 12 V if you know how

youtu.be/Frk3M38mfl4

Perhaps rudeness is not necessary.

Rob Tes said:

you cannot draw an arc flash at 12 Vdc - nor at 15Vdc from a battery charger - its the Physics of the subject (very esoteric)

Yes, arc flash energy at 12 V may well be low, but an "arc" is not "arc flash" - they are two different things.

An arc can lead to arc flash (or not).

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

I appreciate the sentiment, but not quite, so to be accurate.

see The actual law for England and wales

"(1)No person shall carry out any work in relation to a gas fitting or gas storage vessel unless he is competent to do so.

(2) The employer of any person carrying out such work for that employer, every other employer and self-employed person who has control to any extent of such work and every employer and self-employed person who has required such work to be carried out at any place of work under his control shall ensure that paragraph (1) above is complied with in relation to such work.

(3) Without prejudice to the generality of paragraphs (1) and (2) above and subject to paragraph (4) below, no employer shall allow any of his employees to carry out any work in relation to a gas fitting or service pipework and no self-employed person shall carry out any such work, unless the employer or self-employed person, as the case may be, is a member of a class of persons approved for the time being by the Health and Safety Executive 

So

1) To be incompetent and work on gas is illegal.

And

2) No one shall offer themselves as an employee or employ someone to work on to work on gas unless at least one of them is a member of ( in effect Gas Safe)

There are a couple of points there -
1) An individual must be personally registered (employer or employee as applicable), and

2) It says nothing about folk who are neither employers nor employees.

Implying it is not exactly illegal under that act for example to fit your own gas fittings in your own caravan or something, but you must be competent to do so, which may be hard to demonstrate after something has gone wrong and come to the attention of the authorities,  but you certainly cannot do so by way of business without Gas Safe registration.

Amusingly the last survey I saw suggested these rules are also not observed everywhere either, and about 1/3 of things like boilers and cookers sold seem to install themselves magically without any sort of registration with the authorities ever occurring.

In slow time I'll see if I can find a link to that report.

I'm not sure it is a regulation model we should try to emulate.

Mike.

Well said Alan - its this fashion today - started with the concept of dumbing down - that no one is judged as substandard.  Every one's a winner, nobody fails.

Perhaps someone will remind us here of the Political rush (10 + years ago) to coerce all Lecccies to take CnG course to become "Certified Competent Persons"  with the attraction being that this will disable all the cowboys from undercutting legitimate tradesmen who wish to offer professional services.  I remember there was a big fuss, because the Trade bodies ( set up by Gov Minister encouragement) and the Training purveyors were out to make a killing with course fees and subscriptions. Tales of woe abounded, with Tradesmen having to pay out £000's in fees and subs, only to find that the Gov did not follow through with legislation to ensure that only registered competent persons may offer electrician services.  The whole exercise became a huge damp squib and left thousands who had signed up for this accreditation without work as there was still nothing to stop Hairdressers" becomes "Leccies" overnight.  This is still the practice today AFAIK

Contrast this with the Gas Industry, where

It is illegal for someone who is not Gas Safe registered to fit a gas appliance or do other gas work
and then have the work checked by a Gas Safe registered engineer. Both parties would be breaking
the law