Rob Tes said:

Its the method of last resort

Surely this is why BS 7671 requires a means of isolation from every source.

Battery installations use short string interlinks and often have overcurrent protection within, and at the top of, each string ... this, and long runs to combiner boxes, makes the solar PV system very different, and assumptions used to draw analogies between PV arrays and a battery are, in my opinion, flawed.

When we talk about "method of last resort", I'm very mindful of EAWR Reg 14. I'm not sure we have the PV array design right yet ... the risk is not reduced "SFARP" and not enough research has been carried out into isolator fires, "oh well we'll not fit them then" isn't really a good excuse for EAWR Regulation 14 in my opinion.

I should not have to see this method under any circumstances in my opinion ... especially now array voltages are at 1500 V DC ! We can, and MUST have a safer design approach!

Simon Barker said:

So in the case of a short, nothing much happens to the panel, and the wiring needs to be able to handle that current anyway.

Agreed, but it's not just about protection against overcurrent. Arc can still form, or the DC cabling must be made safe to work on.. Detecting it at the inverter end will alert someone to the fault, but if all they can do is cut cables, that's no good !

We must do better and provide a means of disconnecting the source, in line with the requirements of the General Rules of BS 7671, so it's safe to work on cables and connectors which can't be disconnected on-load either .

gkenyon said:

"method of last resort", I'm very mindful of EAWR Reg 14. I'm not sure we have the PV array design right yet ... the risk is not reduced "SFARP"

gkenyon said:

When we talk about "method of last resort", I'm very mindful of EAWR Reg 14. I'm not sure we have the PV array design right yet ... the risk is not reduced "SFARP"

Yes the convoluted EAWR written by lawyers?  I dont see any mention of the "Crowbar" technique.  Isnt this a std method in electrical traction systems for worker protection?

My OP was only concerned with Solar systems for domestic applications and the dangers posed.  We can SFARP if we limit Solar arrays <50Vdc.  IMHO its foolish to allow higher array volts of ca 100V or even 480Vdc (Ive seen on YT probably that Vid posted here)

Facebook

https://www.facebook.com/reel/3507234699527923

I suspect this was several 100Vdc commercial site judging by the length of arc flash

My proposition is to use large knife switches with a gap of ca 50mm for Solar dc<50V.  This system was used in the London underground prewar (600 Vdc).  Its simple and it works. The convenient design of MCBs did away with all the clutter of cast iron re-wireable switch fuse boxes - with their knife switches..

https://vi.aliexpress.com/item/1005003453152419.html?spm=a2g0o.productlist.main.3.5ca41bd96PlNph&algo_pvid=fb3c70a7-cb05-4e87-b7af-a6fa00ac3907&algo_exp_id=fb3c70a7-cb05-4e87-b7af-a6fa00ac3907-1&pdp_npi=4%40dis%21GBP%216.38%216.06%21%21%217.77%21%21%402103853617006671710863788e3ba4%2112000025856398788%21sea%21UK%21929926363%21&curPageLogUid=QOlMH3g17WF6

That humble domestic master switch is a clever robust design - with built-in rewireable strip fuse, (Siemens prewar pattern) and is in use for millions of dwellings in the far east  all for the princely sum of £6  63A rating (could be doubled).  I would trust that..

But roll out the tumbril for I shall be bound for Tyburn Gate and a Public hanging for my heresy.

We can SFARP if we limit Solar arrays <50Vdc. 

Not necessarily - in some ways you're just trading one hazard (higher voltage) for another (higher current).. We're actually quite good at handling several hundred volts around the home (230V a.c. is a bit over 300V pk; and for 3-phase supplies - increasingly common domestically these days - it's over 560V pk) as we generally have the materials and techniques to handle them with adequate safety), especially at modest currents.

My proposition is to use large knife switches

Humm - those simple types need some skill to use safely - fail to open or close them smartly enough and you can cause a lot of damage - from overheating, if not arcing. The less well shielded types risk allowing shorts between exposed parts too.

Detecting it at the inverter end will alert someone to the fault, but if all they can do is cut cables, that's no good !

There's always the option of employing time - wait a few hours and the sun will set

   - Andy.

Rob,

Do you actually understand what you are talking about?

What is a certified and authentic EE ?

Why do you consider that applying a short circuit to a almost constant current supply will cause a roof fire yet a few posts further on suggest a rail traction style crowbar which has the same effect?

I would suggest that rather than YouTube you look at some real information. The guide to ‘Photovoltaics in Buildings’ from the DTI covers most of the points and I would consider it understandable by most competent electricians.

https://files.bregroup.com/solar/Guide_to_the_installation_of_PV_systems_2nd_Edition.pdf

There will always be people who will go for cheap rather than quality but that applies to everything not just Solar PV.

Howdy all.

As always, we do encourage an honest and frank exchange of views but can I please remind you to be civil and respectful of your fellow community members at all times.

Lisa