PV connection to grid

fresun · Jul 28, 2013

This is PV install number 1, which I am presenting for my MCS accreditation this thursday with Napit. System spec: 12 hyundai 250 mono east/west split, power one 3.0 dual mppt.
Out of the Ac isolator in loft with 4mm T&E into an AC isolator in DB cupboard. Now I have the PV 20A CB before the main switch, with the PV output line into the top of it's CB, a single 4mm from the bottom of that CB and into 25mm feed termination on top of mainswitch, the PV neutral straight into mainswitch neutral, again sharing the termination with the 25mm main neutral.

Simple- yes, Minimal fuss and equipment -yes. I believe however it is not best practice to have disimilar cable sizes in the same termination especially 4 & 25mm. Would there be such thing as a termination crimp that accomodates disimilar cables? Any other ideas from the more seasoned sparks/ Solarers out there?
I admit that installs I have seen which use a dedicated second DB do look the business, I am reluctant to re-wire to this spec now for the desire to keep these installs to a minimal viable and safe product, thus ticking the green 'Low impact and sustainable' work procedures. besides with the assessment in a few days it would be a panic job.

hopefully the photos help ,ps the labels on cb's are temporary,

Any constructive input would be gratefully received

Dunc

TedM · Jul 28, 2013

You are correct that it is a 'really bad idea' to have two different conductor sizes in one connection. There is no way the smaller size can be held sufficiently securely.

What you are looking for is called a 'ferrule'. There are twin ferrules available both insulated and uninsulated - in fact there is one on the RCD third right of the main switch in your CU.

I still think it would be a better idea to wire this via a small garage CU.

The Solar King · Jul 28, 2013

Have a look at how they do it in Wylex PV CUs. This is basically a high integrity CU with 2 x two pole switches. Incoming tails go in top of LH switch, Live from PV goes to mcb and N goes to bottom of RH switch. You can also fit an Inepro Din Rail generation meter, making a very neat job. It can get a little crowded if the circuit needs a RCD as well. This meets regs, as if an isolator is required at that end, the 2 pole switch sufices as it now says securable off as opposed to lockable off.

We make up separate enclosures with everything for PV in them and use the same way. Makes a neat job and can save time on site. Alternatively, Andy at Sibert can provide custom enclosures which provide plug and play solutions.

Worcester · Jul 28, 2013

So tell me - how is the live cable between the PV CB and the main switch protected? If it is only 4mm2 The main switch offers no protection, only the DNO's incoming fuse..

High integrity units use 16mm2+ or bus bars until the circuit protection.

If you ran a dedicated CU, the you wouldn't connect it with 4mm to the incoming of the main switch would you?

infinity · Jul 28, 2013

I am with NAPIT Mcs, And my opinion would be do not show him that kind of setup for your initial assessment! I would hope they would give you a N/C for it. There cannot be any reason preventing you doing it properly with a separate CU? You cannot just add MCBs to a side of a main switch in a board not designed to do so it just looks rough IMO.

As far as the fusing goes i believe it would't be a major problem as you can have a certain distance with the cable being back fused from the 16A MCB, but it doesn not make this setup acceptable.

Save yourself the trouble when the assessor is out and change it before hand!

mechelec · Jul 28, 2013

Can you not move the MCBs and RCD to the right of the main switch and fit the Solar MCB next to the garage MCB. You have a high integrity board so that is not a problem but your solution is at best poor and looks a proper cowboy job.
Who the hell fitted the Consumer unit, a blind man? it looks a proper pigs ear, as untidy as I have seen in a long time. If you fitted it which I suspect when you say the labels are temporary, I suggest you get some experience before trying to do this line of work on your own. What training have you had ????????

infinity · Jul 28, 2013

^^^^^ Good Point! I didnt notice that. You all ready have a high integrity board, meaning you have a neutral bar at the top of the board you could use so why have you stuck it in with the main switch?

Put MCB to left of main switch and you have created a way for it, neutral to the top bar and get another busbar to accommodate 3 MCBs instead of the 2 way one there presently.

Gavin A · Jul 28, 2013

as above, you have a high integrity board, what made you think you needed to wire it up that way?

besides with the assessment in a few days it would be a panic job.

are you sure you're cut out for this lark?

We install entire systems in a day - did our first on our house for the inspection the day prior to the inspection as well (which in hindsight was a little rash, but worked out ok), so you should be able to put that right in a matter of well hours at most without any need for panic, just standard working speed.

ps this is what happens with PV systems where the connection on the AC isn't made properly (not ours). Do it right or don't do it at all please.

[ElectriciansForums.net] PV connection to grid

fresun · Jul 29, 2013

Thanks for all the valuable feedback.

Point taken on untidy CU wiring - CU installed by third party, who to be fair had a struggle with my inadequate attempt at enlarging the cupboard. this was prior to myself undergoing C&G levels 2+3 etc. This is now alot more organised I hope.

Labels on CB's rather than CU cover is just untill the CU work is complete.

I have moved the Solar CB inside the mainswitch, before the garage CB. No disimilar cables in same termination or unprotected cable sections as with previous arrangement.
The one doubt in my mind now: Is this a truely dedicated circuit? ie if mainswitch is off, could solar still be providing power to the garage circuit? That said having the Second PV AC isolator next to the CU, is this compliable? If not then I'd imagine that the garage CB should be moved of the main switch / solar buzz bar and onto HMMM, where? The CU set up to have RCDs on both sides doesn't leave any non RCD ways, which the Garage CB would need.

Thanks for the cerebral input in advance

Gavin A · Jul 29, 2013

That's better.

couple of minor niggles - bit too much copper showing for my liking on the live cable from the main switch, and a couple of the MCBs, and your cover isn't on properly on the live bar... though this may have been the previous sparks work, it's probably worth sorting out anyway.

You're right in a way about the main switch, which is partly why we prefer a separate little garage unit for the solar, but any spark is supposed to prove dead prior to working, and should really switch off each circuit they're working on as well as / instead of the main switch, which would make that circuit dead... and there should be a dual pole AC isolator next to the CU for the PV anyway, with a label warning anyone workong on the system to isolate both suppliers before working on it.... you have fitted a dual pole isolator there haven't you?

You can now use a dual pole MCB / RCD / breaker as the isolator, but not a single pole MCB (erm, I think... mutters about regs changing)

eta ah I see from the Op that you have got the isolator in there... you're covered then, as long as you've got the warning stickers as well.

dansk · Jul 29, 2013

just out of curiosity is your PV radial buried deeper than 50mm? or surface mounted?

fresun · Jul 30, 2013

30mA RCD for the PV radial to follow, as regretably the cabling from fuse cupboard to loft were not buried greater that 50 mm or in metalic conduit.

dansk · Jul 30, 2013

;-) just wondering.

Gavin A · Jul 30, 2013

fresun said:
30mA RCD for the PV radial to follow, as regretably the cabling from fuse cupboard to loft were not buried greater that 50 mm or in metalic conduit.

think you passed that test as well.

Someone might mention manufacturers instruction re 100mA RCD, but BS7671 takes precedent in this case IMO, and we've only had one instance of nuisance tripping from a supposedly 30mA RCD protecting a dedicated circuit for a 16amp or lower inverter out of hundreds, and Power-One tech sales agreed it would usually be fine with a single inverter on a dedicated circuit.... so you did right IMO.

PV connection to grid

fresun

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