Repacing consumer unit that has solar PV, question ?

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wizzer

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Hi,

we have a Crabtree Starbreaker split load consumer unit that has 10 mcb's, 5 of which are protected by an RCD and 5 which aren't.

We recently had a 3kw solar PV system fitted and this is wired into the RCD side, from what I have read on this & other forums some say it's ok this way while others say it's best on the non RCD side, so I would appreciate your guidance on this ? It can easily be altered as there are spare ways in the CU.

We are in the process of having an extension built, this will mean that there will be new circuits that have to be connected to the CU, I'm thinking of either replacing the MCB's on the non RCD side with RCBOs or changing the CU for a one that has all RCBOs.

If we were to go for a new RCBO board can the solar pv be fed into a 16A RCBO or would it be best just to use a MCB ?

If we use an MCB would this be classed as compliant ?

Thanks.

 
This is coming up far too often IMHO.

You need to get your pv installers back to sort out their installation. PV should not share RCD protection with any other circuit as it can carry on generating for up to 5 seconds after the RCD has tripped which is against all electrical guidance and best practice

 
Hi,

thanks for the reply.

Due to the advice and discussions on this forum I raised the issue of the PV being on the RCD side with the installer who could see where I was coming from so contacted the MCS inspector for clarification, the inspector said it was ok to be on the RCD side ...I'm sure the reasoning for this was the same as discussed in this thread:

http://www.talk.electricianforum.co.uk/photovoltaic-panels-pv-solar-panels-green-energy-forum-wind-turbines-renewable-energy/20034-definitive-answer-r-e-disconnection-times-final-circuits-pv-inverters.html

From what I have read I can see why the PV shouldn't be on the RCD side of a CU that is supplying other circuits...I agree with that ...but in reality how can I (Joe public) stand there and tell the installer ("The professional") how to do their job, especially as the MCS inspector is telling him that it's correct to put it on the RCD side ?

I had a good discussion with the installer who understood the point I was making, however the inspector is telling him it should be on the RCD side so he is doing what he has been told to do....if he puts the PV on the non RCD side it won't be in line with what the inspector has instructed...no win situation. for the installer isn't it!

Any advice on the RCBO board?

Thanks.

 
It cant comply EVER it would change your 0.4 second disconnection lighting circuit to a 5 second which clearly isnt to BS7671 its dangerous. The best solutions are a seperate board for the PV or one of the Wylex CUs with the dedicated PV split. If it doesnt comply with BS7671 it cant comply with MIS3002 so the inspector is talking utter tosh.

 
Completely agree with nozspark. I've installed loads of pv over the past 12 months... I would either go for a high integrity cu with an rcbo on the unprotected side of the rcd for solar or a separate cu (garage board) solely for the use of the solar. If you don't do this you run the risk of the solar back feeding onto the bus bar and causing nuisance tripping and or altering the disconnection time of the other circuits... Hope this helps

 
Can you guys point me to any official documents that state that the PV should not be connected to the RCD side of a CU that is supplying other circuits?

I will take this up with the installer again and if necessary the inspector but I will need documentation to back up my argument.

Thanks.

 
but in reality how can I (Joe public) stand there and tell the installer ("The professional") how to do their job, especially as the MCS inspector is telling him that it's correct to put it on the RCD side ?
ask, in writing, how the installation complies with the reg about disconnection times

 
... I would either go for a high integrity cu with an rcbo on the unprotected side of the rcd for solar
Virtually impossible to do; as you cannot "backfeed" an RCBo, which is exactly what this would do.

or a separate cu (garage board) solely for the use of the solar. s
In my opinion, the ONLY way to have a clear & concise install, which will comply with all relevant regulations.

Can you guys point me to any official documents that state that the PV should not be connected to the RCD side of a CU that is supplying other circuits?I will take this up with the installer again and if necessary the inspector but I will need documentation to back up my argument.

Thanks.
Ref:

1. BS7671:2011 - 712.411.3.2.1.1

2. stand by:

 
Hi,

I was present whilst the PV installer was doing the tests when the installation was complete, he performed the RCD tests and the test meter displayed a pass result, so if I were to ask for it in writing he will obviously just give me a copy of the results of the test, that isn't going to get me far if they say all is fine.

Am I correct in thinking that the RCD tests that have been done will not be correct because, when the power to the inverter is lost the inverter shuts down, when power is reapplied it takes the inverter 3 minutes to come back on line, so whilst the RCD tests were being performed there was no output from the inverter hence the pass result.

If each of the RCD tests had been performed whilst the inverter was outputting the disconnection times would have been increased....is this correct?

Can no one point me to any official documents that state that the PV should not be connected to the RCD side of a CU that is supplying other circuits?

Thanks.

 
Can no one point me to any official documents that state that the PV should not be connected to the RCD side of a CU that is supplying other circuits?

Thanks.
KME already has above - 712.411.3.2.1.1 - on the ac side, the PV supply shall be connected to the supply side of the protective device for automatic disconnection of circuits supplying current using equipment

 
Its more the fact the RCD trips supposedly disconnecting the power except the inverter will feed in for a further 5 seconds supplying those circuits and if your hanging off the end of one of them thats not going to be good news, nothing to do with the rcd not operating.

 
Sorry for the cut-short response - tea was served ; then a bit of garden work............then some of mr Artois` best work :x

Anyway -

The second ref is The "Electrical Safety Council`s `best practice guide` no. 3" - page 13 para vii and viii

Although this item is a guide ; and compliance isn`t mandatory (same applies to BS7671, which isn`t statutory) ; failure to comply with them is likely to mean failure to comply with building regulations, and MiS3002 (as previously stated).

If the MCS inspector ( whoever he is, and whatever qualification he is supposed to possess) believes this is an acceptable installation - I, for one, would debate that with him, in a court of law if necessary!

Don`t feel too bad about the installer - many of them don`t understand the implications and ramifications of the PV installs, and just "do what they`re told" - sad and wrong; but unfortunately true. I believe the correct technical term is "muppets"

KME

 
It might be time for the IET and others to reconsider their advice to the MCS about what is compliant and what is not. Otherwise, nothing will change. Somebody needs to try and get the big guns involved.

 
Personally I would not connect to RCD side of the CU for all the reasons outlined above, but also in my experience inveretrs can cause nuisance tripping of the RCD under certain conditions. Not had that aprticular problem with anything other than Fronius units, but I'm a great believer in not making trouble for the customers / myself :)

 
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