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Is a DC isolator required on the roof?


PierreJ
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So I'm busy planning the wiring between the solar panels on the roof and the inverter in the garage. I was busy researching which DC isolator to put on the roof when I came across several horror stories of DC isolators failing and even causing fires. Apparently it is a legal requirement in Australia to have a DC isolator on the roof, but the regulation is set to be reviewed due to their presence achieving the opposite of the intended goal which was increased safety.

Are DC isolators required on the roof in South Africa, and do installers typically install them? I scanned through the draft SANS 10142-1-2 regulations and didn't see such a requirement spelled out (but it may be implied perhaps).

Having read all the horror stories of PV fires, I'm also wondering what I should do to protect the cables on the roof and how to bring them through the roof tiles. Is there a guide somewhere that explains best practice in this regard? I'm planning 4 strings of 4 panels, thus [email protected] will be travelling down each of the four wire pairs to the garage where they'll meet in a DC combiner box.

Thanks!

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28 minutes ago, PierreJ said:

Are DC isolators required on the roof in South Africa

That's an Australian requirement, and one that in some cases actually caused the problem it was meant to prevent. The sun eventually kills the enclosure, water gets in, the contacts corrode, and soon the switch causes the fire it was installed for in the first case.

I do not know what the SA regulations say, but far as I know you don't need one on the roof, or even on the outside of the house. Having one in a readily accessible place is a good idea though.

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6 hours ago, plonkster said:

I do not know what the SA regulations say, but far as I know you don't need one on the roof, or even on the outside of the house. Having one in a readily accessible place is a good idea though.

Thanks for the info. I think what I'm going to do is buy a couple of MC4 connectors and use that to connect 6mm^2 PV wire to the panels and then route the PV wire straight into the DC combiner box in the garage. I'll put fuses and disconnectors in the DC combiner box.

How do you normally bring the PV wires through a tile roof? There has to be a better way than flexible conduit and lots of silicone, right?

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8 hours ago, PierreJ said:

Are DC isolators required on the roof in South Africa

As far as I know a isolator is not required on the roof, but it’s best to install a box with fuses on the roof. In your case you have 4 x strings so I would say you need to protect each string with about 15A DC fuses. Preferably two fuses per string. (Negative and Positive fused) This also makes it much safer to work on the roof as you can just pull the fuses for the panels you work on. (Also the fuses will blow on the roof should there be a short circuit on the pv panels, thus preventing fire entering into roof)

 

9 hours ago, PierreJ said:

travelling down each of the four wire pairs to the garage where they'll meet in a DC combiner box.

According to me it would be best to rather run only one thick cable from the roof down to the combiner box to simplify things or two thinner cables if you prefer, but they should be paralleled and landing on a double pole Isolator or circuit breaker in the garage combiner box. 

 

9 hours ago, PierreJ said:

cables on the roof and how to bring them through the roof tiles

There was a discussion the other day where dc wiring from panels must be in steel conduit or it must be a armored cable. I think armored cable will be the cheapest option due to steel conduit requiring more labour and steel conduit is expensive, and difficult to install in tight spaces.

 

2 hours ago, PierreJ said:

There has to be a better way than flexible conduit and lots of silicone, right?

Whatever method you use I think it is going to involve silicone🙂

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9 hours ago, Gerrie said:

There was a discussion the other day where dc wiring from panels must be in steel conduit or it must be a armored cable. I think armored cable will be the cheapest option due to steel conduit requiring more labour and steel conduit is expensive, and difficult to install in tight spaces.

Conduit isn't what it was:

Bosal-Conduit-Brochure.pdf

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10 hours ago, Gerrie said:

Negative and Positive fused

This is important, especially on a corrugated iron roof. When there is the potential that a single earth fault may go unnoticed (one side of a PV array energises the roof), you must fuse both sides.

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19 hours ago, PierreJ said:

So I'm busy planning the wiring between the solar panels on the roof and the inverter in the garage. I was busy researching which DC isolator to put on the roof when I came across several horror stories of DC isolators failing and even causing fires. Apparently it is a legal requirement in Australia to have a DC isolator on the roof, but the regulation is set to be reviewed due to their presence achieving the opposite of the intended goal which was increased safety.

Are DC isolators required on the roof in South Africa, and do installers typically install them? I scanned through the draft SANS 10142-1-2 regulations and didn't see such a requirement spelled out (but it may be implied perhaps).

Not quite a legal requirement in Oz, but virtually so.  The standard requires it, deviation from the standard requires high level engineering justification, compliance is simpler than engineering.  The problem with fires has been due to shoddy isolators/breakers which didn’t comply with the standards marked on them, and with fake MC4 connectors.  They overheat and some of them had non-complaint plastics bodies that did not self extinguish as required.  Presumably in RSA unlicensed work is limited to somewhere around 120-145 VDC, so the importance of the isolater/breaker properly carrying the load is even more important due to the higher currents.  Should you use double pole, non-polarised thermal breakers for the task, even if the part is deficient, the heat should cause it to open circuit before the smoke gets out.  To the best of my knowledge, the notion of removing isolation from the panel array has not been broached to the standards committee (it is a standard, not a regulation, each state has their own law/regulations which reference the standard as a means of compliance).  One response incorporated in the standard has been a requirement for sheltering the devices from the weather and UV - IP56NW  standards may not have been met by the flaming devices, or, much more likely, it may not be installed properly, compromising the device and letting water in, which doesn’t help.  The other thing is the housing deteriorating from UV.  Both SA and Oz enjoy low levels of atmospheric pollution, particularly with regard to ozone, so our UV levels are often ten to fifteen higher than Europe, Asia and North America, this damages the plastics IP56 housings - hence the Oz standard requiring non-combustible shelters.  In practice, a folded piece of stainless sheet is used.

 

The following article has a lot of educational pictures at the end showing things going wrong;

http://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/

 

You’ll note a lot of MC4 initiated fires.  MC4 is Tyco power, not a generic name.  The cheap copies of MC4 cause a lot of fires.   Both the Aussie standard and the RSA draft require you to use connectors from the same manufacturer on each joint, to reduce the fire risk, many having been caused by the reverse engineered product being not quite the same...  If you are worried about fire, worry about this.

 

You’ll also see a lot of tide lines and rust in failed isolators and switches.  Drenching the connections in conductive soup doesn’t end well...  

 

The idea of having isolation where you are working is a very good one, you can keep an eye on it.  Decades ago I was in water to my waist down a bore hole installing a 440V pump motor, I had just installed the last wire and was about to put the wiring cover on, when it started turning.  The owner had arrived, cut the lock on the isolator with the “Danger do not remove” tag, reinstalled the fuses and turned the pump on.  Others haven’t been so lucky, hence the idea of isolation at both ends - it’s a good one.  If you can do it with decent fittings that won’t catch fire and protect it from the elements, I’d commend it as a good idea, even if your standards don’t require it.  The other reason for isolators on the array is to give firefighters a way to protect themselves, which would be of little use in RSA, as they wouldn’t expect it to be there.

 

May I suggest the use of doublepole thermal DC CB at your array combiner box?  This will help you protect yourself from fools.  In my opinion, they are generally are not as good as fuses for dealing with fault currents, so you may prefer fuses as well.  But if you can get an IP56 fuse enclosure that protects you from live conductors when you open/close it, that would probably do everything you want.  Also, make sure you use drip loops on every cable entry point.  Including ones inside or on a protected outside wall - and try to use side or bottom entry to the enclosures.  You could also put weep holes at the bottom of conduit drip loops.

 

Your RSA draft standard looks very well written.  Electrical standards are often written in blood, meaning that specific clauses often relate to specific fatal accidents.  Thus, although your drafters are clearly very intelligent and must have looked at other jurisdictions to try to learn without exacting a blood price, they may not have anticipated every issue.  Don’t confine your thinking exclusively to the standards, lest you contribute blood to a future revision.  Your concern about causing fires is very well founded and an inability to isolate at source, should some numbskull break your isolation at the other end likely won’t cause more than inconvenient arcing and equipment damage, but does have the potential to kill you, through another fault being present or through the combination of things you are touching at the time, such as might happen installing a pair of MC4 onto cables.

 

On some installations I do something a little  naughty, where the enclosure isn’t mounted level, I drill a few weep holes on a corner edge that is parallel with the ground.  If water gets in, in future decades and no one ever inspects it, instead of accumulating, it has a chance to get out.  However, for deniability, not quite getting the sealing 100% correct on a bottom conduit entry can achieve the same thing.  I suspect drainage requirements will be a future direction in the standards, the nature of elastomer seals is such that they tend to fail with time.  The problem is that so often they only let the water in, not out again.

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12 minutes ago, Paul Saccani said:

The problem with fires has been due to shoddy isolators/breakers which didn’t comply with the standards marked on them

Yup, as I recall the manufacturers recalled some of the switches. Dave Jones (the EEVBLOG guy) actualy had an issolator fail on his roof and made a video about it.

13 minutes ago, Paul Saccani said:

The owner had arrived, cut the lock on the isolator with the “Danger do not remove” tag

If you died... that would have been murder (by Dolus Eventualis). A reasonable person would foresee that doing such a thing could get someone killed. I assume you gave him an earful?

14 minutes ago, Paul Saccani said:

drill a few weep holes

My most memorable application of this method was on the tail light of a VW golf MK1. I drilled a 2mm hole in a spot where you could not even see it. Water-in-tail-light issue solved.

15 minutes ago, Paul Saccani said:

not quite getting the sealing 100% correct on a bottom conduit entry can achieve the same thing

I believe the Americans call it a drip loop 🙂

 

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On 2020/03/07 at 9:41 AM, Paul Saccani said:

May I suggest the use of doublepole thermal DC CB at your array combiner box?  This will help you protect yourself from fools.  In my opinion, they are generally are not as good as fuses for dealing with fault currents, so you may prefer fuses as well.  But if you can get an IP56 fuse enclosure that protects you from live conductors when you open/close it, that would probably do everything you want.  Also, make sure you use drip loops on every cable entry point.  Including ones inside or on a protected outside wall - and try to use side or bottom entry to the enclosures.  You could also put weep holes at the bottom of conduit drip loops.

Thanks for all the good advice. After scrolling through all the images of burnt out solar panels I am now thoroughly scared of DC wiring, and I'm wondering whether I shouldn't perhaps get someone with more experience in these matters install the panels for me.

Does anyone have first-hand experience with an installer in the Somerset West area that they can recommend?

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1 hour ago, PierreJ said:

Thanks for all the good advice. After scrolling through all the images of burnt out solar panels I am now thoroughly scared of DC wiring, and I'm wondering whether I shouldn't perhaps get someone with more experience in these matters install the panels for me.

There are very good reasons to be afraid of DC! It is way more hectic than AC.

I agree with your thinking of getting someone to do the job. (The problem is finding someone who is capable!)

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On ‎2020‎-‎03‎-‎07 at 3:57 PM, plonkster said:

Yup, as I recall the manufacturers recalled some of the switches. Dave Jones (the EEVBLOG guy) actualy had an issolator fail on his roof and made a video about it.

If you died... that would have been murder (by Dolus Eventualis). A reasonable person would foresee that doing such a thing could get someone killed. I assume you gave him an earful?

My most memorable application of this method was on the tail light of a VW golf MK1. I drilled a 2mm hole in a spot where you could not even see it. Water-in-tail-light issue solved.

I believe the Americans call it a drip loop 🙂

 

I believe that something in the order of 16 different isolators have been recalled, not all from shonky Chinese brands, but all made in the PRC.

With regard to Dolus Eventualis, that would not be applicable, as he genuinely believed (bizarrely, in my view) that he was alone on the premises and did not foresee a risk to anyone.  The standard is subjective, not about what an objective reasonable man might think about the actual facts.  This guy was a retired RSM I had known in the Army as both responsible and reliable, I was doing this job as a favour to help him out.  What he did was very out of character and reflected a lot of personal stress and sleep deprivation etc...   His wife had died, he had young kids to look after and a stressful job.  Yes, I did make some rather pointed comments to him indicating that I was not well pleased with his actions, but they were not delivered in a harsh tone.  Though of course the first one was a cry of "WTF were you thinking!".

I'm not sure about what American practice is with regard to drip loops and what they define them as.

Drip loops are a standard cabling practice that many neglect.  I use it for top entry too.  If using a conduit, you do tend to need a weep hole, otherwise you are creating nothing more than an S bend like a toilet, the water will eventually enter your enclosure.  Of course, if you use something like a Shepard's crook at the other end, that should stop water flowing down the conduit.  Drip loops also need to be used for cable that is not enclosed.

The other benefit of a drip loop is that it provides stress relief for a cable.   The reason that electricians often avoid their use is simple, it uses more cable and therefore costs more money.  You also have to consider in these DC wiring cases that the extra length will increase cable losses slightly.

If you look at some of the pictures in that web link, you'll see cases where wall mounted isolators have had top entry, no drip loop and have filled up with water causing failure.  Most electricians are lacking in day to day experience with low voltage DC (below 1,500 VDC), though as I recall the training differences between Western Australia and SA, in SA they are certainly trained for it - it just isn't day to day for most in both countries, though of course, this solar business has changed that.

 

 

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12 hours ago, PierreJ said:

Somerset West area

You're a Somerset Westian too... 🙂 Man, we seem to be THE place for solar power around here. The Blue Nova boss also lives here.

I am not at all sure who to recommend around here. Green Sun maybe (Blackheath side). ExSolar always does a good job, but they tend to be a bit pricey. The guy I usually recommended went a bit SolarEdge crazy and he has a bit of an anti-blue bias these days, so that's out too. IMHO... get the best guy for the job even if you have to import him from another town. IE, get Mike Thorne if you can.

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15 hours ago, plonkster said:

ExSolar always does a good job, but they tend to be a bit pricey.

I got several quotes and ExSolar was actually on the lower end of the scale, particularly on the Victron hardware. Perhaps others in the region are taking advantage of the situation and coining it. Hardware prices have certainly shot up in the last couple of weeks, more than the weaker exchange rate can explain away.

Seeing that I'm getting the hardware from them, perhaps it would be best if they handle the panel install as well. Then at least there can't be any blame ping-pong between the hardware supplier and installer in the event that something doesn't work.

By the looks of things my build will only come to fruition in several months' time: I'm at the back of the queue for a Victron Cerbo, and I still haven't been able to source Pylontech batteries. It's disappointing, but at least it gives me plenty of time to iron out all the kinks in the design.

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8 hours ago, PierreJ said:

Hardware prices have certainly shot up in the last couple of weeks

Victron is flying in the hardware instead of using normal "by ocean" shipping because it sells out so quickly. That might account for some of the extra costs. The exchange rate only really slipped in the last week or so (it was R18.62 to the Euro last night... I could hardly believe it), so that will not be reflected in the price YET...

I learned yesterday that Orbic Solar operates in our area as well (based in Hermanus it seems), and the pictures of their installs that I've seen look fairly good. They are also advertising like mad on Facebook... so one would hope they actually have a bit of stock to put behind the ads... 🙂 Maybe give them a try too.

8 hours ago, PierreJ said:

back of the queue for a Victron Cerbo

Yup, that turned out to be extremely popular and sold out like hot cakes. But why do you want a Cerbo? Is a Venus-GX not good enough? Or are you after the nice touch screen? 🙂

8 hours ago, PierreJ said:

still haven't been able to source Pylontech

Yup, that's the big issue at the moment. The battery makers can't keep up. Pylontech doesn't ship by air, since it is batteries and considered dangerous goods, they can't really do it either. It takes a lot of effort to ship batteries by air. They have to be mostly discharged, can't be shipped with certain other goods, ceertainly can't fly on a passenger plane...

You could of course talk to the SolarMD guys... or you could ask ExSolar if they can source you a FreedomWon battery.

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2 hours ago, plonkster said:

But why do you want a Cerbo? Is a Venus-GX not good enough? Or are you after the nice touch screen? 🙂

I'm hoping that the wi-fi range of the Cerbo is better than the Venus. I'm not going to buy the screen, but it's nice to have the option of adding it later. (Apparently you can plug in any HDMI display and mouse - the ports are not proprietary.) If the Cerbo was more expensive I would have considered a Venus, but they're pretty much in the same price range. It's clear to me that the Cerbo is intended to replace both the CCGX and Venus, so it's also a case of not wanting to buy something that will be obsolete soon.

 

2 hours ago, plonkster said:

You could of course talk to the SolarMD guys... or you could ask ExSolar if they can source you a FreedomWon battery.

I've gotten several quotes on various lithium batteries, including FreedomWon. It's hard to look past the price. I have not been able to find anything that comes close to the Pylontechs in kWh/Rand terms.

I'm also fearful of buying one big monolithic battery in case something goes wrong with it. I'm not going to blindly assume that the battery manufacturers are going to be around to honour their 10 year warranties, but at least with the Pylontechs if one goes bad I can toss it out and still have a working system.

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3 minutes ago, PierreJ said:

wi-fi range

I advise people to as far as possible use a wired connection. Wi-Fi works (and more improvements is coming in Venus 2.60), but right now it's not very stable at all.

The Cerbo is significantly faster than the other two though, so I too would favour that one. There is no real danger of the others becoming obsolete any time soon.

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