Solar PV house fires, BRE report

[torbrowser]

https://assets.publishing.service.g...solar-pv-systems-industry-recommendations.pdf
Sobering reading for anyone thinking of installing solar PV or even experienced installers.

My take on this report is,

DC arcing is almost always the cause of fires
Most DC arcing occurs in the PV string isolators
Then DC connectors - MC4 plugs.
Inverters are down the list of causation.
Out of the DC isolator fires, a large part is from incorrect installation, then the isolator being unsuitable for DC, some of these isolators are rebadged AC isolators. (suspect the ones i have may be these)

My opinion on this is, general sparks (myself included), assume a PV system is just a simple plug and play install, are not familiar / experienced with DC systems and don't appreciate the extra care needed with it, very unforgiving. Combine this with a mass of low quality electrical equipment on the market that just about gets away with working on an AC system and i'm not surprised there has not been more fires.

 

[johnb2713]

Why do you feel DC is unforgiving just out of interest?

 

[binky]

you're only talking about 40 fires in that report if I'm reading it correctly. How many appliances burn out a year?

Poor MC4 connections are definetly an issue - certainly the main cause for earth leakage faults on the roof, and I've fixed quite a few of those. These are down to the installers, and failure to buy £2.50 MC4 spanners.

AC isolator has 3mm air gap on contacts, DC isolators have 6mm Air gap on contacts, some DC isolators are AC units with a link between 2 terminals, so 3mm + 3mm = 6mm. Installers sometimes take the links out, and use both teronals, but as this is only a problem when isolating the DC, then I would suspect any isolator fires are just poor terminal connections, as long as the AC isolator is correctly voltage rated. I've only encountered this once, fortuantely it was in an external box and fire did not spread to the house.

Inverter fires, again only once on the AC connector - poor workmanship most likely cause, although one Chinese brand did seem to have an issue with this as I inspected the neighbours and found the same connector was scorched ( could have been same installer of course).

 

[johnb2713]

DC has the ability to maintain an arc as opposed to AC extinguishing 100 times per second. In the steelworks we had some hefty DC equipment that had an airblast fired when the contactors or breakers opened to blow the arc out, very noisy and quite intimidating.

 

[Murdoch]

These numbers are ONLY GOING TO RISE, given the amount of DIY installs going on.

I do find it amazing that the DNO's don't ask for EIC's for the installs that do back feed into the grid

 

[binky]

DC has the ability to maintain an arc as opposed to AC extinguishing 100 times per second. In the steelworks we had some hefty DC equipment that had an airblast fired when the contactors or breakers opened to blow the arc out, very noisy and quite intimidating.

Had an interesting fire caused by a plumber core drilling through the DC cables. It burnt about a foot up the wall before finally going out. Scared the crap out of the plumber

 

[Murdoch]

Had an interesting fire caused by a plumber core drilling through the DC cables. It burnt about a foot up the wall before finally going out. Scared the crap out of the plumber

were the cables in a safe zone

 

[torbrowser]

Good replies, Thanks.

Great explanation Binky on the 3mm vs 6mm airgap on the isolators. Been looking for an explanation why the strings pass through 2 poles.

Agree with Murdoch re the DIY installs, - that's what mine is, i have no prior experience with PV, ( do tiny caravan and motorhome installs count ? )

John, unforgiving in that any mistakes results in bigger chance of burning connections.

 

[binky]

were the cables in a safe zone

Yep, plastered into an external wall in plastic capping. Unfortunately that coincided with where a poo pipe needed to exit a bathroom . This was a new build property. I can't say I was too upset as the customer stole the services of a subby I was using at the time. Said subby has never worked for another contractor in my area since, serves him right for stealing a customer. Trust is everything in business.

 

[johnb2713]

John, unforgiving in that any mistakes results in bigger chance of burning connections.

From a contact point of view I disagree, it's only when arcing starts it's harder to stop eg opening an isolator, damaged cables or a bad connection, the air stays ionised and theres no let up. In terms of passing through isolators and connections theres no difference IMHO.

 

[binky]

From a contact point of view I disagree, it's only when arcing starts it's harder to stop eg opening an isolator, damaged cables or a bad connection, the air stays ionised and theres no let up. In terms of passing through isolators and connections theres no difference IMHO.

That's the fun bit! I used to do maintenance work on a solar farm which has been built with lots of rubbish 20kw inverters. I forgot to isolate the DC when changing a failed inverter one day. So having pulled a corroded MC4 , but not completely freed it from inverter I was rather surprised to see a little blue flame at the connection. That turned to a small panic as I realised it wasn't going out .

 

[torbrowser]

From a contact point of view I disagree, it's only when arcing starts it's harder to stop eg opening an isolator, damaged cables or a bad connection, the air stays ionised and theres no let up. In terms of passing through isolators and connections theres no difference IMHO

Thanks John,
I think we actually agree rather than disagree !

 

[torbrowser]

I have booked myself onto a BPEC PV course, BP-SPV-3, start it week next Wednesday.

You can all tell me its a shit course and waste of time now !

How this course will teach me to push MC4 connectors together any better afterwards i'll have to let you know.
Still, you can never learn enough.

 

[torbrowser]

Well i am now a qualified PV installer.

3 Days out of my life and £600 i won't see again, for anyone considering these courses it's a bit like a regs course, the object is to read a book and pass the exam so the tutor looks good.
Good bits, 2 hours in the workshop doing the testing and shading calcs and the classroom bit doing the kWh/kk values, the rest was just scanning through the book.
My ability to click together MC4's remains the same.

What i really need is a manufacturers course to really learn the set up and functions of the inverter.

 

[Murdoch]

Do they ask for any electrical qualifications?

 

[johnb2713]

What i really need is a manufacturers course to really learn the set up and functions of the inverter.

Victron have some decent online courses free of charge, I've done a few relevant to my inverter and they were half decent.

 

[torbrowser]

Thanks, will have a look.

 

[torbrowser]

Do they ask for any electrical qualifications?

Yes, they take your particulars before hand.

 

[SPECIAL LOCATION]

https://assets.publishing.service.g...solar-pv-systems-industry-recommendations.pdf
Sobering reading for anyone thinking of installing solar PV or even experienced installers.

My take on this report is,

DC arcing is almost always the cause of fires
Most DC arcing occurs in the PV string isolators
Then DC connectors - MC4 plugs.
Inverters are down the list of causation.
Out of the DC isolator fires, a large part is from incorrect installation, then the isolator being unsuitable for DC, some of these isolators are rebadged AC isolators. (suspect the ones i have may be these)

My opinion on this is, general sparks (myself included), assume a PV system is just a simple plug and play install, are not familiar / experienced with DC systems and don't appreciate the extra care needed with it, very unforgiving. Combine this with a mass of low quality electrical equipment on the market that just about gets away with working on an AC system and i'm not surprised there has not been more fires.

I noticed the report in your link is from July 2017.,
Is there any more up-to-date statistics on PV fires that isn't 5years out of date?

 

[torbrowser]

There will be statistics published every year by various fire departments, try gov.uk web site, pretty much every statistic can be found in there somewhere.
Link your findings back on here - will be interesting to see how the figures have improved / got worse.
Jack.