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.

 

[jibjob]

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.

Ok, I was (mistakenly?) going by what the client told me. I've learnt alot of useful stuff this evening. At least now I can go back with the EICR completed with issues observed & recommendations on how to bring it all up to spec

 

[moggy1968]

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.

sorry Gavin, I wasn't sure which bit you were questioning, although I did answer both aspects in my post.
In view of the complexities of the arguments on shared RCDs I would be inclined to play it safe and put it on it's own dedicated RCD. It becomes part of the regs if it prevents the RCD tripping correctly but is not (as far as I am aware) specifically a part of the regs that PV must have it's own dedicated RCD.

 

[Gavin A]

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.

but an RCD trips due to a live>earth fault (or neutral earth fault) somewhere on the circuit... where is the return path from earth to the inverter once the dual pole RCD has tripped?

If there's no return path to the inverter from earth, then there should be no danger from a live>earth fault.

At least that's how I've understood it.

 

[Earthstore]

My understanding is, an RCD trips because of an imbalance between live and neutral, so a live to earth could cause this,
IE man touches live cable, as he is earthed (unless he is flying) this would cause an imbalance between live and neutral so RCD trips therefore cutting off the live and neutral in 0.4 of a second so all is safe.

If PV is on a shared RCD then the same man would get the live from the PV for up to 5 seconds going through him to earth, it could also put the power into any fault for the 5 seconds.

I could be wrong, but this is my layman's understanding of it.

 

[moggy1968]

there is also some concern that interference currents induced by the PV could prevent the RCD from operating at all, but this is going over old ground. I'm not 100% convinced either way, which is why I wouldn't share an RCD.I would rather play it safe!

 

[BruceB]

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.

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

What we do not know is whether the fuse board drawn is actually a fuse board or say a 16th edition consumer unit. If it is the former then the rcd is probably 30mA and best not to share it as it will be providing the 40ms protection Earthstore refers to, although as we have discussed before the ESC BPG does allow it to be shared. If it is a 16th edition consumer unit already with 30mA rcd for socket circuits, then the rcd might be a 100mA or greater and be a time delayed one protecting for TT reasons. If it is that then I would not have a problem personally 'sharing' the rcd and leaving it as the single point of isolation.

The criminal point is that there is no overcurrent protection.

 

[SolarCity]

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

Perhaps from a damaged cable on the roof that comes into contact with a bonded frame or extraneous roof structure?

On this subject, I've often pondered if there is any real danger to firefighters as the DC side of the inverter shouldn't be referenced to earth anyway.

 

[BruceB]

Perhaps from a damaged cable on the roof that comes into contact with a bonded frame or extraneous roof structure?

Yes, with a transformerless, but that should get picked up by the RCMU with most such inverters and already have tripped it out.

 

[jibjob]

Whilst that is true, as one of the sides of the inverter output is not referenced to earth then there would be no danger from that unless a second fault to earth was also present.

What we do not know is whether the fuse board drawn is actually a fuse board or say a 16th edition consumer unit. If it is the former then the rcd is probably 30mA and best not to share it as it will be providing the 40ms protection Earthstore refers to, although as we have discussed before the ESC BPG does allow it to be shared. If it is a 16th edition consumer unit already with 30mA rcd for socket circuits, then the rcd might be a 100mA or greater and be a time delayed one protecting for TT reasons. If it is that then I would not have a problem personally 'sharing' the rcd and leaving it as the single point of isolation.

The criminal point is that there is no overcurrent protection.

Tis a Wylex box with plug in retro fit BS 60898 MCB's. Standalone 30mA RCD upfront, which is shared with PV as shown in my drawing. RCD? maybe, maybe not, overcurrent/short circuit protection definately.

Thanks guys for all your help

 

[SolarCity]

The lack of overcurrent protection is jaw-dropping. I can't believe that an electrician could actually make such a fundamental error.

 

[jibjob]

The lack of overcurrent protection is jaw-dropping. I can't believe that an electrician could actually make such a fundamental error.

To be honest, doing what I do, lots of domestic testing & lots of maintenance, I come across it a fair bit, showers being the most popular one. Shower has been added to an existing install, with a 6 or 10 mm T&E straight out of the main switch terminals & thru a standalone 30mA RCD completely bypassing any form of OPD. Baffling

 

[sedgy34]

To the OP just test the ac side from the inverter, your not qualified to mess with the DC side (no offence)

 

[Gavin A]

To the OP just test the ac side from the inverter, your not qualified to mess with the DC side (no offence)

bit unnecessary that wasn't it?

The OP hasn't mentioned the DC side anyway, but would probably be better qualified than whichever twunt carried out the initial installation

 

[Gavin A]

To be honest, doing what I do, lots of domestic testing & lots of maintenance, I come across it a fair bit, showers being the most popular one. Shower has been added to an existing install, with a 6 or 10 mm T&E straight out of the main switch terminals & thru a standalone 30mA RCD completely bypassing any form of OPD. Baffling

probably mistaking the rating of the RCD for being the overcurrent trip value of the RCD... tbf it might be that the RCD will burn out before the cable, but that's not exactly a recognised method of over current protection

 

[sedgy34]

bit unnecessary that wasn't it?

The OP hasn't mentioned the DC side anyway, but would probably be better qualified than whichever twunt carried out the initial installation

I did say (no offence) it's fact

 

[jibjob]

Been doing this job for a while now and I'm well aware of my limitations. While no offence was taken it's probably not a great idea to be making assumptions about peoples qualifications. Seen many a topic on this forum take a nose dive when the mud slinging starts :smilewinkgrin:

 

[sedgy34]

Been doing this job for a while now and I'm well aware of my limitations. While no offence was taken it's probably not a great idea to be making assumptions about peoples qualifications. Seen many a topic on this forum take a nose dive when the mud slinging starts :smilewinkgrin:

I didn't assume about your qualifications with Pv YOU actually said in your first post matey :50:

 

[jibjob]

I didn't assume about your qualifications with Pv YOU actually said in your first post matey :50:[/QUOTE
]I know what I said. You said I wasn't qualified to mess about with DC. I think you'll find there's more than just one application that involves DC.
Anyhoo, the forum has once again provided me with some useful info in relation to my original post & I'd like to thank those people who contributed, gotta go now, Doctor Who is on

 

[bkh]

Thank you all, this thread has been very helpful!