EICR - PV Install

[jibjob]

Hi All,

Carried out an EICR a couple of days ago on a domestic property that incorporates a PV install that I'm not totally sure about. I have no experience in terms of installing or testing PV systems but understand the basic principle of how it should work, ie generating electricity from the sun's rays via an array & an inverter thus providing free electricity. This is the first time I have carried out an EICR on an install with PV.

According to the client the system is only used to generate electricity to feed back into the grid. She was unable to provide me with any certification (installed approx 3yrs ago) or a schematic. Couldn't find it apparently. I have drawn a layout of the install, apologies for it being a bit rough. Does this look right? Should there be over current protection? I'm a little confused by the 2nd AC isolator which is situated in the meter cupboard which houses both meters shown, RCD, fuse board & cut-out. This isolator cuts mains power to the digital meter & the inverter when switched off (as does the RCD).

Any help would be appreciated.

 

[Earthstore]

AC isolators, one near inverter to make safe if working on inverter, the other is at an accessible location, hence why there is two, DC isolater that is good too.

I can see two problems here;

1 AC cable is probably too small so may send the inverter overvoltage, especially if grid voltage is on the high side. (what length is the AC cable and what size system is it?)

2 It looks like it is on a "shared" RCD, something that is a big no no for PV sytems for several reasons.

I hope this helps.

 

[Earthstore]

Just one other point, there have been several threads on the merits of RCD protection on here just search RCD PV and you will find several.

 

[jibjob]

AC isolators, one near inverter to make safe if working on inverter, the other is at an accessible location, hence why there is two, DC isolater that is good too.

I can see two problems here;

1 AC cable is probably too small so may send the inverter overvoltage, especially if grid voltage is on the high side. (what length is the AC cable and what size system is it?)

2 It looks like it is on a "shared" RCD, something that is a big no no for PV sytems for several reasons.

I hope this helps.

Hi Earthstore,

Thanks for your reply. Cable run is probably 7/8 metres, the RCD is existing, making it a shared RCD, system is TT BTW. Basically the RCD is fed from incoming mains with the load going to the fuse board & AC isolator in front of digital meter.

 

[Earthstore]

If you know the size of the system then do a cable loss calculation for the AC cable, it should be less than 1% not the normal 3%, it might be just within tolerance but I would prefer to see 4mm or even a 6mm cable.

A PV system can take up to 5 seconds to shut down, your RCD should be what 0.4 of a second, so even if it trips the PV could be poking power into the house for that 5 seconds, also it is possible that the PV system could balance out a fault so the RCD may not trip at all, PV on a shared RCD can cause nuisance tripping also.

 

[Worcester]

From an EICR aspect
1) The PV installation should have overcurrent protection (consider the mains in as source)
2) The PV system, if it is / needs to be be RCD protected should have it's own dedicated RCD. Depending upon the inverter type and installtion methodology it may not need an RCD.


1) Could be achieved simply by housing a double pole MCB in a simple two gang enclosure (as available from CEF for main switches as incoming isolators) - fed by tails from a Henley block meter side of the RCD - so you might want to put an isolator there as well. Or if you need an RCD as well - rating 30mA / 100mA depends upon type and make of inverter, then a garage CU may be a better option. Main switch, rcd, mcb; though of course depending upon how you read the regs, the main switch may sometimes be omitted as the rcd, so long as it switches both poles may be able to do that function.

From a PV aspect - depending upon the size of the pv system and length of cable, the 2.5mm2 may be undersized from a voltage drop aspect.

- - - Updated - - -

Update, TT the inverter should be on it's own dedicated RCD

 

[Gavin A]

should there be overcurrent protection?

definitely - that's got to be a straight fail without overcurrent protection on 2.5mm t&e coming straight out of the main RCD like that.

I'd think that'd be a dangerous installation notice situation, though tbh I don't do EICR's so haven't ever needed to issue one.

bang a little CU in there with a 16amp MCB in it and you can sleep soundly... no idea how the previous spark could leave it like that.

 

[Gavin A]

Update, TT the inverter should be on it's own dedicated RCD

Is that actually a requirement or a recommendation?

We'd split the tails and install a separate RCD anyway, but if it's TT presumably it'd be a 100mA or 300mA RCD existing, so I doubt that nuisance tripping would be an issue in most cases would it?

I guess I ought to know the answer to this question, but as we do it anyway whether a requirement or not, I can't remember if it is a requirement.

 

[moggy1968]

Gavin: Any circuit on a TT system needs to be on an RCD. Given the debate on the use of Shared RCDs I would definately say it should be on it's own seperate one.

I would split the tails in a henley block, then have the PV in it's own dedicated CU.

It does need overcurrent protection at the CU, 16A will do.

I would have used 4mm AC cable but 2.5 may be ok, you would have to do the calcs.

You would probably get away with using a 30maRCD, I've only had problems with one once, although the Inverter manufacturers recommentsdation is probably 100 or even 300ma so you may want to take a view on that!

Rectifying the problems isn't a massive job TBH

The absence of certification is a concern

 

[jibjob]

Thanks to everyone for the advice, I'm beginning to get my head round it now.

If I've got this right, ignoring the size of the cable for a moment, then best option would be to henley block tails before existing RCD into an enclosure containing a DP RCD/Main switch & OCPD (16a MCB). Then send my 2.5mm2 on it's journey to inverter via AC isolator & digital meter as shown on my work of art from OP.
As mentioned before it's simply feeding into grid & not providing the house with any generated power.

 

[jibjob]

Gavin: Any circuit on a TT system needs to be on an RCD. Given the debate on the use of Shared RCDs I would definately say it should be on it's own seperate one.

I would split the tails in a henley block, then have the PV in it's own dedicated CU.

It does need overcurrent protection at the CU, 16A will do.

I would have used 4mm AC cable but 2.5 may be ok, you would have to do the calcs.

You would probably get away with using a 30maRCD, I've only had problems with one once, although the Inverter manufacturers recommentsdation is probably 100 or even 300ma so you may want to take a view on that!

Rectifying the problems isn't a massive job TBH

The absence of certification is a concern

I should learn to type faster, I think you've answered my last question, many thanks

 

[Gavin A]

Gavin: Any circuit on a TT system needs to be on an RCD.

I know that, my question was whether it actually has to be on it's own dedicated RCD on TT, or can be on the shared RCD.

My thoughts would be that it'd be ok on the shared RCD as it's only going to be around 10mA leakage current from the inverter, leaving a good 90mA spare for leakage currents from other circuits... though there is the issue that if it trips, it trips everything.

 

[Gavin A]

Thanks to everyone for the advice, I'm beginning to get my head round it now.

If I've got this right, ignoring the size of the cable for a moment, then best option would be to henley block tails before existing RCD into an enclosure containing a DP RCD/Main switch & OCPD (16a MCB). Then send my 2.5mm2 on it's journey to inverter via AC isolator & digital meter as shown on my work of art from OP.

sounds good

As mentioned before it's simply feeding into grid & not providing the house with any generated power.

have another look at the diagram - it is feeding the house as well as the grid as it's on the house side of the suppliers meter, so energy generated will get used in the house in preference to grid electricity, then either excess will be exported, or if the house requires more power it will import.

at least it will if your artwork is accurate

 

[Earthstore]

Thanks to everyone for the advice, I'm beginning to get my head round it now.
As mentioned before it's simply feeding into grid & not providing the house with any generated power.

No, if the house is using 3kw and the system is producing 3kw it would use the pv, if the house is using 4kw and the pv is producing 3kw it would use 3kwpv and 1kw mains, if the house is using 1kw and the pv is producing 3kw the it would use 1kw pv and export 2kw pv back into the grid.

Hope that makes.

 

[Earthstore]

My thoughts would be that it'd be ok on the shared RCD as it's only going to be around 10mA leakage current from the inverter, leaving a good 90mA spare for leakage currents from other circuits... though there is the issue that if it trips, it trips everything.

But as the PV can take 5 seconds to shut down it could still be live on the "tripped" side of the RCD for those 5 seconds not the required 0.4.