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