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Install of PV System from Midsummer...


BenP
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Afternoon, 

 

I'm having no luck finding a local electrician to connect up our solar pv! The main electrician for our build is being very diligent having never touched it before which is fair.... 

 

Anyway. Panels are all up on the roof awaiting connection.... I need to get the scaffold down in the next two weeks. I'm thinking I can get the DC cables run to the two isolator switches (12 panels in 2x6 config) pretty easily?

 

So would I, mount DC isolators, connect 4mm cables to isolators with other ends ready with MC4s, ensure isolator in off position and then connect the panels in their correct sequence? 

 

Failing that - any recommendations for Kent based electricians? 

 

Ben

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I'm not a scheme member and tbh only dabble. I know absolutely jack about solar either.

 

Would @Binky know of someone this neck of the woods?

 

 

Edited by Onoff
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Are they optimised? If not, beware of getting frazzled installing these during the daytime.

The real risk is going + to - per panel in sunlight, or the then elevated risk of connecting a string and getting quite high DC available across the sum of the string. Pretty serious, life changing juice available per string.

If you make the single core DC cables off to the rotary isolator first, then lock the isolator in the off position, and work back from there up panel by panel you will reduce the risk ( not eliminate it ).

If you have any doubt, please do not carry out this work.

 

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24 minutes ago, SteamyTea said:

You will have to re-type @Binky so he gets a message.

Not seen him on here for a while.

 

I think @Binky is the @Binky from the electrician's forum that @ProDaveand I know from there. I think I pointed him at this forum but can't remember.

 

Something happened with my account at TEF and I couldn't get back in. Not been on there for months.

 

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I’ve been competent with complex 1ph and 3ph electrical design and installation projects, in both the domestic and the marine environment, and am taking delivery of my own panels imminently. I’ll be completely honest, even MY arse is twitching over the DC-related-death likelihood. I’ve had more AC shocks than I can remember ( memory loss probably caused by these lol ) and only one got me worried, but DC is a different beast altogether. 

 

As an aside;

It would be such a shame to die now, as my children are 11, 13, 15 and 18 years of age now, and over the last few months I’ve started to become quite fond of them……. 

Edited by Nickfromwales
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Anybody know if the Tigo optimisers drop the open-circuit voltage to <1v ( like the Solaredge ones do? ).

 

Apologies for the hijack, blame the beer. I am COMPLETELY innocent.

 

 

Disclaimer: Innocent when sober = questionable at best.

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Thanks for all the words chaps. 

 

This setup isn't optimised ASFAIK. 12x Trina panels going to a Sofar inverter. 

 

Any local contacts would be useful. I'll start harassing the local MCS contractors a bit too today. 

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Just listening to the prophets of doom citing death as close to inevitable when connecting PV modules got me thinking of what seems a more realistic situation???

OP has 2 strings of 6 panels wired into separate isolators so max voltage on either string is around 6x40vdc=240v. That 240v will be contained within a pre wired isolator. The pre wiring has an IP2x MC4 connector on the end of whats probably double insulated cable. Panels are new almost certainly having a factory QA inspection for function and integrity. Remembering that the isolators arent connected to anything yet and are in the off position,  theres no circuit that can carry any current so youre not connecting any load. When you plug the first panel in youre handling MC4 connectors with circa 40 volts across them inside IP2x connectors, IF you held both plugs at once, which you dont when connecting up

When you connect the second panel to the first theres no voltage across the plugs as both panels arent referenced to earth or to each other. The same principle applies as you plug in subsequent panels.  When you connect the last panel to the isolator cable, theres now 240v inside the isolator but as the array isnt tied to earth, youve got to touch both +ve and -ve at the same time to get a belt, after youve taken the cover off the isolator.

Maybe Im missing something but it seems pretty benign to me???

 

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Yes that is in principle how it works.  you must terminate the cables in the DC isolator first.  Then you must confirm insulation resistance between DC cables is good, i.e. you have no damaged cable no nails through the cable and most important have not messed up the wiring of the isolator and created a short circuit.  Then lock the isolator in the off position.

 

Then plugging in the panels one at a time in series should be safe, but I still prefer to do the last connection at dusk when the output from the panels will be small.

 

Remember DC is much more dangerous.  The alternating nature of ac will likely throw you off if you touch something.  DC won't do that so is far more likely to be very serious.  250V dc is not something you want to touch.

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Or cover the panels with black plastic or card, then there should be no volts.  Connect without any risks.

 

Assuming you've done everything Dave mentioned above first.

Edited by JohnMo
Added word "panels"
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1 hour ago, Dillsue said:

Just listening to the prophets of doom citing death as close to inevitable when connecting PV modules got me thinking of what seems a more realistic situation???

OP has 2 strings of 6 panels wired into separate isolators so max voltage on either string is around 6x40vdc=240v. That 240v will be contained within a pre wired isolator. The pre wiring has an IP2x MC4 connector on the end of whats probably double insulated cable. Panels are new almost certainly having a factory QA inspection for function and integrity. Remembering that the isolators arent connected to anything yet and are in the off position,  theres no circuit that can carry any current so youre not connecting any load. When you plug the first panel in youre handling MC4 connectors with circa 40 volts across them inside IP2x connectors, IF you held both plugs at once, which you dont when connecting up

When you connect the second panel to the first theres no voltage across the plugs as both panels arent referenced to earth or to each other. The same principle applies as you plug in subsequent panels.  When you connect the last panel to the isolator cable, theres now 240v inside the isolator but as the array isnt tied to earth, youve got to touch both +ve and -ve at the same time to get a belt, after youve taken the cover off the isolator.

Maybe Im missing something but it seems pretty benign to me???

 

I'm pretty much with you on this. I wired up all my panels myself, you would have to be doing something very wrong to get a shock.

 

It's easy to do and as long as you are careful I'm not sure what the issue is🤷‍♂️

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1 minute ago, LA3222 said:

It's easy to do and as long as you are careful I

I agree, I would work from  the AC end backward towards the panels, testing as you go, connecting the panels up last (with insulated plugs). (I plan a DIY instal later this year).

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I don't see any issue, yes voltage can be high, yes it could kill you, but as long as your not being blinking daft you will be fine.

 

Wire up all the fixed stuff from the mains connection to the DC isolator, that can all be done safely with full isolation. Then wire up your DC cables into your isolator(s) BEFORE they are connected at the other end to the panels, then with the DC isolator(s) OFF, you connect the solar string(s) - at this stage no load will be on the panels so no current shall be flowing, so no arcing or sparking and the circuit will be open so there won't even be a spark, carefully, without sticking your tongue and pinky finger into the ends of the MC4 connectors, push them together until they click. You can now fire up your system, usually AC on first, then DC side - but follow manufacturers instructions for first power up. I know my inverters are different, 1 will do nothing until it sees DC, so commissioning during the night or without PV connected is actually impossible (unless you have a string emulator), the other will fire up and just go into sleep mode. 

 

Look at it this way, how many PV installers work at night?

 

 

 

 

 

 

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It’s when you assume nothing can / will go wrong, and you don’t exercise diligence, that's when it does go wrong.

This forum dispenses advice, so take that as good advice, or with a pinch.

 

Time on the tools, hands-on practical experience, qualifications etc cannot be replaced by a few paragraphs here.

Nobody yet mentioned that they did / did not carry out the checks as per @ProDave‘s comment above, so we can assume they were blissfully unaware of the risks posed by NOT doing so and then self installing their PV.

 

I’ve heard enough horror stories, and instances where an individual has been electrocuted, to be less blasé.

 

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Worth adding that a time when things can go very badly wrong is if you try and disconnect a panel that is supplying load.  Another feature of dc is it is constantly on, no zero crossing that you get 100 times a second with ac. So if you disconnect a dc circuit under load, you will get a much bigger arc that won't be self quenching like ac.  That is why you MUST shut down the inverter and then open the dc isolator before doing any work.

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2 minutes ago, Radian said:

I'm going to post this highly informative video again. It might surprise some people.

 

 

Nice demonstration.  EXACTLY what will happen if you try unplugging one of those nice insulated MC4 connectors while under load.  It is not so safe and fool proof now is it?

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