Solar farm earthing

[loplug]

Been doing some work today on a solar farm , from the subs there are 95mm 4 core Alu cables running out to the arrays where there is a box that splits the feed between the 2 inverters. Now the cable that comes from the sub is connected to the neutral bar at the mccb panel and marked with blue sleving at the array end it is marked with green and yellows sleaving and connected to bothe the inverter earth and neutral connections. This to me is wrong but what is the correct set up for earthing a solar farm should the inverters be earthed locally from the frame and earth mat system ? Or some other PEN system?

 

[loplug]

dont seem to be geting many responses

 

[loplug]

before

After

 

[Gavin A]

struggling to work out what you're saying the situation is, but the pictures obviously look to be wrong. Needs stripping out and redoing sensibly.

Sounds a bit like someone's not understood about using the armours as the earth or maybe misunderstood about grounding the neutral on the DC side (not usually needed, but is sometimes mentioned in manufacturers instructions).

 

[infinity]

Is the armour used as the earth?

 

[BruceB]

It does look odd. I'll have a go at identifying a few points, but I think I agree with Gavin that it needs stripping out and re-doing.

- Is that armoured cable coming in? With those colours (the fourth core being G/Y not blue) it might not be SWA but RV-K.

- If it is armoured then the armour must be earthed.

- If the fourth core is G/Y it cannot be used as a N, but could in principle be a PEN conductor if other rules are met.

- It appears to have a combined neutral and earth (ie PEN). Although 7671 534.4 allows this sometimes, basically you cannot do it in 'consumer' installations in UK. ESQC reg 8(4) says so. So rather than simply being against non-statutory regulations (7671), it is probably against the law and subject to a fine at level 5 (£5k I believe) on the standard scale.

- 7671 would allow a PEN conductor up to that box and for it then to be split into N and PE if a) it had not been previously split and re-combined in the installation, and b) you had 'authorisation'. But given ESQC Regs and assuming it is a grid connected consumer installation, I cannot see how you get authorisation in UK.

- Do the inverters require a neutral?

More investigation or detail required for certainty.

 

[Gavin A]

Is the armour used as the earth?

it'd appear not from the photos, actually hard to tell it it's even SWA, if not then that's a lot more problematic as there is no separate earth, it looks as if it's got a plastic gland entry so erm.

Looks to me as if someone's ordered and pulled through the wrong cable, then attempted to bodge it.

 

[loplug]

there is no armour on the cable the green and yellow core is conected to the neutral bar at the dist board end which has a link to the earth bar and yes the inverters do require a neutral

 

[davesparks]

They appear to have set it up as a TNC system, with cores correctly marked for this under the current version of bs7671. But that part of the regulations only really exists just in case there happens to be an old TNC installation in existence which needs to be altered or repaired, so they have to make rules for it. I don't think it has been allowed in new installations since the 13th edition.

 

[loplug]

i think it needs to be set up as a TT system now with an earth coonection at each array but i dont know what the normal set up is

 

[davesparks]

It needs another conductor to each point whatever you do, the regulations require a cpc connected to the earthing system in use at the source of the circuit to be present at every point on a circuit.

 

[loplug]

which reg is that i thought most dnos did not alow the export of pme and it is common place to have tt systems in out buildings fed from pme suplied distboards

 

[davesparks]

Yes, but you still take the cpc to the final point of termination, usually in the form of the cable armour, but don't connect it at the load end. You set up the independant TT system at the load end of the supply.

 

[davesparks]

Oh, and you can't export PME, you can only extend the equipotential zone.

Exporting would require shipping it into another country!

 

[loplug]

yes but is the cpc not only there to earth the armour and if it was a double insulated cable unnecessary

 

[davesparks]

I think that would be a departure from the regulations, but would obviously require design justification.

I should think solar installs are a bit different anyway as the inverter is the source of the supply, not the load!

 

[loplug]

I think that would be a departure from the regulations, but would obviously require design justification.

I should think solar installs are a bit different anyway as the inverter is the source of the supply, not the load!

only in sunlight

 

[davesparks]

Yes, but it is still a source of supply at those times, that is the whole point of the system!

As far as I know multiple sources running in synchronisation need to have a single common earthing system.

 

[Engineer54]

Looks as if the two smaller cables in that panel are SY cables ( those with the braided earth link between them) which is a no-no for external cabling before you start to worry about the earthing system....

Is there no ''Approved'' distribution/layout drawings available for this solar farm installation, at least then you'd know what the system design concept is or was, and if it has been altered by others??

 

[Gavin A]

where does the separate earth cable go to that runs out through the bottom of the box?

 

[loplug]

yes that is sy going to the inverters but i know that that is wrong but thats not part of what i have been asked to do at the moment.is there a reg that disalowes sy out side or is it just the manufactures specification?

i havent seen any drawings just been instucted by a consultant from the firm that built it because the company that will be running it wont exept it as it is. when i have questiond what they have asked me to do ive just been told to get on with my work.


the earth wire goes to one of the steals that support the array

 

[Engineer54]

How the hell can you assess this new build solar farm's electrical installation without having the access to the drawings to which it was built too??

EDIT... What work remit exactly have you been instructed to carry out to this Solar Farm and why isn't a technical representative of the company that built it, not come to site to check for themselves what deficiencies (if any) are existing on this installation?? I don't suppose you know the details either, of why the other company are not
accepting the the installation as it stands??

Something sounds a bit fishy here!!

Manufacturers cable description will give you that, these SY cables are not UV protected and the outer transparent sheath will soon start to deteriorate. Some manufacturers will even state not to be used as prime current carrying conductors, they are designed in fact for control/machine wiring and the like....

 

[TedM]

http://www.elandcables.com/Eland/media/assets/product-pdf/SY-Control-Flexible-Cable-to-BS6500.pdf

Can be used outdoors when protected.

SY Cables are not suitable for direct connection to the public mains supply.

IMO the installation is unsafe, unfit for purpose, should be immediately disconnected until redesigned and reinstalled by someone who knows what they are doing.

loplug, you cannot fix a broken leg with a sticking plaster.

 

[loplug]

IMO the installation is unsafe, unfit for purpose, should be immediately disconnected until redesigned and reinstalled by someone who knows what they are doing.

loplug, you cannot fix a broken leg with a sticking plaster.

i agree it should be redesignd and reconnected i cannot see them disconecting it as that would cost them money.

who broke there leg?

does any one know what the normall or an exepted methood of connecting the inverters to the supply?

 

[Engineer54]

I'll ask again, ...What work remit exactly have you been instructed to carry out to this Solar Farm

 

[loplug]

Just to change the connection in the boxes from the first picture to the second picture. So disconnecting the earth neutral from the 4 pole isolator and resleaving then strip the blues leaving from the 95mm

 

[Engineer54]

Well without access to any drawings you can't very well say too much. I'd get on and complete the work contracted to undertake and submit your invoice, perhaps giving some written notice of anything that you consider as deficiencies that you have found. It's then down to this other company that is going to be responsible for the running and upkeep of this solar farm installation, if they are now happy or NOT with the limited remedial work you have provided?? .. lol!!