Urgent Advice please on connection of AC from inverter to quad CSU setup

[dw89]

Hi All,

Many thanks in advance for any advice, I know this is the place to ask:blush5:

Basically I am a 'consumer' who's having a pv array fitted and I want to check what the contractor's intending to do. I built my current house so I don't want it going up in flames! Unlikely but I'd rather check here first than have something go wrong.

So, I'm clear on everything apart from AC connection from inverter to CSU. I have FOUR CSU's (single phase 18kVA); First 'main' CSU (in garage) takes tails from meter and supplies power to THREE sub-main CSU's (one on each of three floors) via 16mm T&E. Each of them are 10-way Volex dual RCD (one for sockets, one for lighting). I have been told (and not being an PV expert in any way) that they will connect to one of the CSU's (happens to be one on top floor - in warm-roof living space) using a spare way. My questions are as follows:

1) If they connect the AC supply from inverter to this 'sub' CSU surely the power generated will 'only' be available to that CSU and the sockets/lighting connected to it (i.e. everything on top floor) and other floors/equipment will not benefit? It's important to me that the power generated is available to the whole house so how does this work? Is it ok to connect to this sub-CSU or should the connection really be made via SWA through the ceiling voids to the main-CSU which provides power to all the sub-CSU's (i.e. one in garage)?
2) Is it ok just to connect straight to an RCD protected MCB like this in a unit that is already protecting lighting and sockets? I just saw, when googling, this post...which has prompted my worried question here! http://www.electriciansforums.co.uk...m/51532-ok-connect-ac-cable-mcb-consumer.html It may be, of course, that they've just not told me everything but I just want to check obviously because in the wake of the details in that post.

I especially want to get this right as, ultimately, I want to get a PowerWall fitted when they arrive in the UK next year. Oh, and just so you know, equipment will be JA Solar (panels, inverter, optimisers etc).

Any and all suggestions greatly appreciated.

KR, Dave

 

[Worcester]

Which Inverter? That makes a difference

Just as an aside, an 18kVA connection is unusual, even though you may have 80A / 100A incoming fuse, the DNO supplies are usually rated at 15kVA

The house will use the PV generation first, irrespective of which CU it is fitted to.

IN principal it is OK to fit the inverter to a submain CU, so long as the cable connecting it to the main CU is of sufficient size.

How big a PV system are you having fitted. generally PV AC cable conenctions are 2-3 sizes large than normally required for the current flow as you are only allowed a 1% voltage drop from the inverter to the incoming vs 3% for the distribution cable. At 16mm2 I'd be surprised if there would be a problem.

Yes it's OK to fit it to an MCB.

Is it OK to fit on a shared RCD? that depends upon the type, make and model of inverter.

Generally most good PV installers will try to design out the requirement for an RCD if possible.

Are you on a TT or TNC-S (PME) earthing system?

 

[Worcester]

Oh, and why are are you asking here.. If your already doubting your installer.

Get them to expalin fully why they are doing it the way they are.

If you are an avid DIYer, then read this : http://www.microgenerationcertification.org/images/PV Book ELECTRONIC.pdf

Why are you having optimisers fitted? Do you have an unusual roof arrangement or shading issues? Or did they send round a slick salesman?

 

[Gavin A]

1- no the power will flow through the house, so that's fine.

2 - It generally shouldn't be on a shared RCD as this is likely to cause nuisance tripping, apart from other potential concerns about the impact on RCD functioning to protect you in the event of a fault.

 

[TJ Anderson]

Interesting the level of confidence the installer has instilled in you yet is still carrying out the work. These questions should be directed at him that you are then satisfied to carry on.

 

[TJ Anderson]

1- no the power will flow through the house, so that's fine.

2 - It generally shouldn't be on a shared RCD as this is likely to cause nuisance tripping, apart from other potential concerns about the impact on RCD functioning to protect you in the event of a fault.

Gavin, it specifically should not be on a shared RCD as the G83 inverter can output upto 5 seconds after mains disconnection so it could maintain a supply onto an earth fault after the RCD had operated and back feed through PV MCB through the busbar and onto that circuit.

 

[Gavin A]

Gavin, it specifically should not be on a shared RCD as the G83 inverter can output upto 5 seconds after mains disconnection so it could maintain a supply onto an earth fault after the RCD had operated and back feed through PV MCB through the busbar and onto that circuit.

there is an argument that it then becomes a separated circuit without a return path for the earth fault to the power source, but I didn't want to get into that as it's a bit complex, hence my comment.

 

[dw89]

Hi Guys,

Thanks for all the replies, just checking some details and then will reply again.

Cheers, Dave

 

[dw89]

Ok, first of all equipment will be:
JA Solar 3680 Inverter (well 16A 4000 model)
15x JA Solar 265W panels with Optimisers 'in' the panels - JAM6(R)(BK)60-265
Basic Ofgem meter, AC/DC isolators etc
House supply is 18kVA, single phase (I found/checked voltage on supply paperwork), 100A fuse.
Earthing is TN-C-S from 'main' CSU in garage to gas pipe.
As said, from 'main' CSU it supplies, via x3 separate runs of 16mm T&E, x3 sub CSU's (one on each floor) which supply all lighting/sockets to house.

Idea, for me at least, is to get in (just) before FiT's go down (it was always planned from day of build but I got a bit out of touch and didn't cotton on to the FiT's going down until last month!). Then, next year, I'm thinking about the Tesla PowerWall along with the JA StorEdge Interface (basically it's the reason I was going for JA over, say, Fronius). On top of that, being a programmer, I am told there's an API to the JA Inverter that can be unlocked with a 'key' of some kind, which means I can tap into it for Home Automation purposes (i.e. for readings etc - whatever the API allows really).

So, firstly, why Optimisers? They didn't add much to the cost of the panels and, I assume all being JA, that it adds at least some efficiency benefit over 20+ yrs to make the @£2-300 cost back. I could be wrong but hope not It was, of course, suggested but was cheaper to have them integrated in panels rather than 'add' them to each panel at double the cost per unit.

Why, as Worcester asked, am 'I' asking? Well, human nature really! Whenever you come on a forum where people have expertise where they are kind enough to give that expertise/advice for free I feel you get a genuine honest answer and you get multiple answers from which one can make a judgement. However no matter who you employ, in whatever nature, in the real world, as soon as profit is involved, there's the inevitable possibility of things being left out, added unnecessarily or, as you said, possibly being sold things that are not required! So, it's just a case as I said, of me trying to head off any possible issues before they arise rather than having to argue etc after the fact, get someone back etc. A good example of this being the awful install I saw on here of the guy who's landlady had an £7k install of cheap rubbish and there were no stickers, no isolators etc etc. He came on here for advice and I'm just doing due diligence I guess I am sure they 'will' do a good job but knowledge is power and you guys are being good enough to help add to that. Hope that answers On top of that 'I' had seen it installed in a separate way in a standard CSU before and 'assumed' this was correct, my installer stated he was adding one and I asked if it was needed due to the fact I had spare ways. Whether he was agreeing with me because he thinks its 'what I want' (i.e. please the customer) or whether it 'is' right I simply don't know for 'sure' hence the questions! Finally the guy who visited wasn't a spark so asking him what seemed to be a 'non-standard' qu (i.e. 4 CSU's) I didn't think would get me very far on the basis of the other qu's I asked him so if I know then I can speak to the spark directly.

On the technical replies I'm understanding the following:
1) If it's connected to 1 'sub-CSU' it's connected to them all via, I assume, the 16mm connecting T&E?
2) But still slightly confused on the connection of AC inverter output to CSU connection as one reply says it's ok, another says should be separate and then second reply from first contributor says 'should' be connected as otherwise earthing fault 'may' not be spotted if it's separated from system (which also makes sense). So, is there not a 'standard' in 17th etc edition for this particular kind of install or ?

Again many thanks all for taking the time to reply and thanks for the link, I will have a read first chance I get.

KR, Dave

 

[whinmoor]

It sounds like you are getting JA Solar panels with embedded Solar Edge optimisers. The central inverter is from Solar Edge (not JA). We've used this configuration a couple of times with positive results.

It should be compatible with Storedge & Tesla Powerwall when released next year.

 

[Worcester]

We report all our Solar Edge installs both to the SolarEdge monitoring site and also to PVoutput.org which makes it easy to compare with other installations in the near vicinity.
We've got one site which we cannot find out why the main board fuses keep blowing (despite power data logging and analysis), inverter #5 in 12 months...

So we've answered Q1

re Q2 Ftom SolarEdge Installation manual:

If an external RCD is required by local regulations, check which type of RCD is required for the relevant electric code. SolarEdge recommends using a type-A RCD. The recommended RCD value is 100mA or 300mA unless a lower value is required by the specific local electric codes. When required by local regulations, the use of an RCD type B is permitted.

So NO, it must be on a separate RCD from any other circuits, or on a non RCD circuit if that can be designed out. - bear in mind if the supply to the sub CU is on an RCD circuit (which should of course be a time delayed one for discrimination) then you won't be able to connect to that CU and will need to run a dedicated supply cable form the incoming side of the main CU. (Germany requires type B RCD's)

 

[dw89]

Whinmoor: yes, you are spot on I've been told (by company) and seeing literature that Powerwall will work with it. If it doesn't I'd be more than unhappy with them!

Worcester: each 'sub' CSU has twin RCD's (one for lighting, one for sockets). The 'main' CSU (in garage) which supplies a) x3 'sub CSU's b) smoke/heat alarms and c) garage sockets does indeed have an RCD....though I am not sure if it's a time-delayed one or not to be totally honest. If I check the board and give you the code will you know if it is? The guy who did all the electrics (an old friend) was a very good spark but it's always possible that something 'could' have been missed...I don't know. So, from what you've said and what I've confirmed I have, it sounds like I need the following:

1) New 'two way' CSU, supplied from incoming main supply before 'main' garage CSU which will have
2) An RCD (of ? nature)
3) The other way being the connection from the solar pv to be installed.

So, my other question on this basis would be regarding placement of items. The panels will be on the other side of the house (i.e. furthest away from garage as possible! Around 20m of cable at a guess). So what is the best plan for cabling? i.e.

Should I
1) Have inverter in loft to minimise DC cable from panels to inverter (just a meter or so) and have 20m of AC cable to garage OR
2) 20m of DC cable, Inverter in garage and minimal AC cable.
3) In both options above, what T&E and DC cable size should be used?

What's worth bearing in mind is the placement of the Tesla Powerwall which, at 100kg, is probably best in garage (though 'could' be catered for in loft due to construction). I don't know, in advance, if there are/will be restrictions on length of cable to/from it and how it may relate to option/s 1 and 2 above. I just want to make sure one resolution doesn't cause another problem down the line! Ultimately I'm sure you have much greater knowledge on this subject than I do.

KR and thanks again

Dave

 

[jestur]

Dave,
similar here in terms of wanting to get ready for possible storedge and powerwall. on the solaredge website they have a storedge document that goes into details re max cable lengths etc. I had my Inverter sited in the garage (integral) so that powerwall can go next to it along with the storedge and required powermeter.
No idea on prices for storedge / powerwall yet, but it was actually neater to site the inverter in the garage (other side of the wall from the utility meter) so no real harm done and hopefully the best solution for future upgrade.
see http://www.solaredge.com/files/pdfs/preparing_for_storedge_upgrade_on_grid.pdf for info

 

[dw89]

Thanks Jester, Sorry for delay in replying but I didn't get a notification for some reason so missed it! Will look at that doc today.

Any helpful answers anyone on the rest? All very much appreciated

KR, Dave

EDIT:

Hi All, just read Jestur's document and it covers just how far the Tesla should be from the inverter. However I still need to know the wiring implications as per my above post because, if I install inverter etc in garage rather than plant room (to get access to main CSU), then this is @20m away from the PV strings. So I just need to check basic requirements on wiring as per qu's in post. Thanks v much guys.

 

[dw89]

Been told that they will use an RCBO in the sub-csu. I know nothing about RCBO's or whether it's suitable or not. What do you guys think? I ask as noone mentioned this I believe so opinions appreciated.

KR, Dave