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NozSpark

The one point that I'll pick up on is that they removed RCD protection for the circuit.... the regs while the regulations are not retrospective, any work that we do has to comply with the regulations that are in place at the time that the work is carried out,,, so if this cable is buried <50mm in a wall, goes through a metal frame stud work or passes through a bathroom then it needs RCD protection... the best way to achieve this of PV would be to protect it with a RCBO or through it's own consumer unit with appropriate fault and overload protection... as for the type of RCD that it should have,,, I'd say that an "AC" type RCD is no longer appropriate for a new installation or alteration of a PV circuit and that an "A" or possibly even "B" type RCD would be better suited

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binky
6 hours ago, rugbyduffy said:

 

 

1. I'd asked them to provide documentation of this modification for my own records, insurance purposes, etc. They seemed surprised that I'd requested this and stated that they could provide a Minor Works Certificate for me - is this the appropriate documentation for this work? 

 

seems reasonable to me, it's not a new circuit as such, and not a new MCB, so the electrical characteristics haven't really been changed. 

 

6 hours ago, rugbyduffy said:

2. I have been reading the available extracts of BS7671, in particular "522.6.202 Cables in wall less the 50mm from the surface" which I realise stipulates that I require 30mA protection for this circuit - my solar PV cables are within safe zones in plastic capping under render.   Now that this circuit has been modified am I required to comply with this (presumably more recent) regulation? I say 'presumably more recent reg' as I believe this was a 2015 update, which our home pre-dates (built 2012).

 

rediculous as it may seem plastic capping is regarded as 'mechanical protection' same as plastic trunking, ergo any need for RCD is removed in my opinion. I would not be looking to reroute cables to suite 2018 regs or citing current regs as a reason to do so, it is not a new circuit.   Would have to rewire half the houses in the UK if we did. As it stands it is compliant with 2012 and only thing required is the OCPD (cable protection) , so as long as that complies with requirements for overload protection, ie right size MCB then that is fine. Moving cct off RCD has just enhanced your safety. Inverter shut down times can be as long as 3 seconds (in reality most work far faster) so RCD could be tripped out whilst you are cutting through your lawn mower cable and you still get belted by your PV system for up to 3 seconds, rather than 40mili-seconds RCD normally takes to trip. This could kill you!  

 

6 hours ago, rugbyduffy said:

3. Assuming so, is my only option an independent 30mA RCBO for the the single PV circuit, and hope that without any cumulative leakage effects from the "okay, not great" circuits that this will survive my Sunnyboy inverter switching?

 

Sunny boys aren't normally as issue on their own RCD - I still prefer no RCD.  

 

6 hours ago, rugbyduffy said:


4. I have read a lot of manufacturer advice relating to PV nuisance tripping RCD which focuses on uprating to 100mA or 300mA ratings! Am I right to presume that these are applicable only in cases where cables are routed differently to mine, effectively snookering me (as ours were installed in build, not retro-fitted)?

 

See comments in previous discussions.  Power One are effing terrible for earth leakage after being bought out by ABB, my own earlier model Power One has no issues with earth leakage. Later models after a couple of years leak like a sieve hence need 300mA RCD to cope. I've had several long arguments with their technical support and got precisely no where with any complaints, and stopped fitting these invereters - they used to be my favourite unit. Not known earth leakage to be an issue with any other make of inverter. When installing cables I've always routed to avoid RCD requirement under current regs, but any requirement is not retrospective. 

 

6 hours ago, rugbyduffy said:

5. Assuming I do need a 30mA RCBO and this suffers similar nuisance tripping, are my only other options to redesign the wiring routes to not require the RCD protection (Regulation 522.6.204 I think stipulates such examples?), or to upgrade our Inverter which is presumably deteriorating somewhat due to the increased frequency of RCD tripping and its 8 year age (I think we were suggested these had a potential life of 10yrs when we purchased the system, although I got the impression the industry was so new that nobody actually knew this as the time we were quoted it).

 

SMA I would expect to last 15 - 20 years unless subjected to a large voltage spike form something like a lightning strike in your local area, we are still in the dark about actual inverter life, but SMA design for 20/25 year life. 10 years is sales BS for flogging new inverter upgrades or getting foot through your door on pretence of 'safety inspections' or some other BS to sell you other stuff you don't need! The earth leakage issue will not be the inverter on its own, all modern appliances have some earth leakage to protect the electronics, so a build up of earth leakage from multiple sources eventually gets to the magic 30mA (in reality probably more like 25mA) that causes RCD to trip.

 

Hope that helps. 

 

 

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binky
2 hours ago, NozSpark said:

The one point that I'll pick up on is that they removed RCD protection for the circuit.... the regs while the regulations are not retrospective, any work that we do has to comply with the regulations that are in place at the time that the work is carried out,,

 

Interesting point, would correcting a mistake still be subject to todays regs? In this case, inverter should never have been put on a shared RCD (not really known at the time), so moving it off RCD has improved safety, corrected mistake, but not involved any alteration of the cct or OCPD. In my opinion, any requirement to work to current regs is not applicable or a bit over -zealous? If the cct was being alterred to say, add a socket, a modification to the cct, then I would agree with your point.

Edited by binky

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NozSpark
2 hours ago, binky said:

 

Interesting point, would correcting a mistake still be subject to todays regs? In this case, inverter should never have been put on a shared RCD (not really known at the time), so moving it off RCD has improved safety, corrected mistake, but not involved any alteration of the cct or OCPD. In my opinion, any requirement to work to current regs is not applicable or a bit over -zealous? If the cct was being alterred to say, add a socket, a modification to the cct, then I would agree with your point.

 

I'm sorry, but it's a buried cable.... it needs RCD protection...... whilst moving the circuit off a shared RCD has made the installation as a whole safer, removing RCD protection from that cable has made that circuit less safe

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Murdoch
9 hours ago, NozSpark said:

 

I'm sorry, but it's a buried cable.... it needs RCD protection...... whilst moving the circuit off a shared RCD has made the installation as a whole safer, removing RCD protection from that cable has made that circuit less safe

 

Isn't the simple answer replace  the MCB with a RCBO?

 

I find that some nuisance tripping (on dual boards) is due to accumulated leakage across the circuits - seen it more on "16th" boards where all the sockets are RCD protected

 

22mA isn't hard to achieve in the average house

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binky
15 hours ago, NozSpark said:

 

I'm sorry, but it's a buried cable.... it needs RCD protection...... whilst moving the circuit off a shared RCD has made the installation as a whole safer, removing RCD protection from that cable has made that circuit less safe

 

but capping counts as mechanical protection.

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Sharpend
1 minute ago, binky said:

 

but capping counts as mechanical protection.


not sure that it does. 

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Murdoch
16 minutes ago, Sharpend said:


not sure that it does. 

 

Doesn't that depend on how thick it is and what it's made of? 😀

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binky
30 minutes ago, Murdoch said:

 

Doesn't that depend on how thick it is and what it's made of? 😀

 

never seen any 'guidleines' refering to mateial or thickness. Personally I think plastic capping is about as much use as a rich tea biscuit against a drill bit or screw. 

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SPECIAL LOCATION

Most capping is designed so that it can be nailed to a wall...

 

Therefore it cannot be considered as mechanical protection for buried cables...

 

As bullet point (iv) of 522.6.204 specifically states mechanical protection will prevent penetration by nails / screws etc..

 

You can use an 'earthed metallic covering' to protect buried cables..

 

But capping's main function was to protect a cable from the plasterers trowels etc.. 

From the days of wet-plastering, when putting on the first bonding coat.

hence why plastic capping was an acceptable cheaper alternative to metal..

 

With so much dry-line boarding done nowadays..

many don't bother with any form of capping at all over the cables to be hidden behind the boards. 

 

bottom line is.. if you can hammer a nail through it..

It is NOT mechanical protection!

 

Guinness 

Edited by SPECIAL LOCATION

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Sharpend

Concur with Spec as my understanding. 

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rugbyduffy

Thanks everyone for your expertise and guidance! 

 

Thanks to @binky for taking the time to respond to each of my queries, and to @NozSpark, @Murdoch, @Sharpend and Spec @SPECIAL LOCATION for continuing the debate and providing your own thoughts and interpretations.

 

So what I take from your responses:

  • Plastic Capping is unlikely to be classed as suitable ‘mechanical protection’ per the definitions (I must say as homeowner I wouldn’t feel comfortable in relying on it for this purpose);
  • Assuming this, I would need to reinstate the RCD protection of this cable which I have lost since the modification (recognising I have actually made all of the circuits previously shared on the common RCD safer by eliminating the issue of the inverter shutdown lag). The reason for this is that the 17th edition wiring regulations BS7671 cover my system as they apply to all installations after 30th June 2008.
    (An alternative to this would be to re-route the cabling so as not to require RCD protection, which isn’t really practical as its wet-plastered into the walls since the house was built.)
  • My SMA inverter on its own 30mA RCD is not likely to be an issue with nuisance tripping by removing the cumulative earth leakage from the previously shared circuits.
  • The easiest means of achieving this would be to replace the MCB with an RCBO which will add earth fault protection and maintain Overload protection for the PV circuit.
  • An ‘AC’ type RCD is not appropriate for this application and I should seek an RCBO with ‘A’ or ‘B’-type characteristics; I presume my installer will be able to advise on the exact type from OEM recommendations, but any thoughts on this from the experts?
  • The previous MCB move didn’t require a Minor Works Certificate as this wasn’t a new circuit or MCB. On that basis if this were to be replaced with an RCBO should I expect to receive a Minor Work Certificate (or other paperwork for my records)?

Thanks again for all of your times and wisdom.

Cheers,

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rugbyduffy
On 05/11/2020 at 12:25, rugbyduffy said:

Thanks everyone for your expertise and guidance! 

 

Thanks to @binky for taking the time to respond to each of my queries, and to @NozSpark, @Murdoch, @Sharpend and Spec @SPECIAL LOCATION for continuing the debate and providing your own thoughts and interpretations.

 

So what I take from your responses:

  • Plastic Capping is unlikely to be classed as suitable ‘mechanical protection’ per the definitions (I must say as homeowner I wouldn’t feel comfortable in relying on it for this purpose);
  • Assuming this, I would need to reinstate the RCD protection of this cable which I have lost since the modification (recognising I have actually made all of the circuits previously shared on the common RCD safer by eliminating the issue of the inverter shutdown lag). The reason for this is that the 17th edition wiring regulations BS7671 cover my system as they apply to all installations after 30th June 2008.
    (An alternative to this would be to re-route the cabling so as not to require RCD protection, which isn’t really practical as its wet-plastered into the walls since the house was built.)
  • My SMA inverter on its own 30mA RCD is not likely to be an issue with nuisance tripping by removing the cumulative earth leakage from the previously shared circuits.
  • The easiest means of achieving this would be to replace the MCB with an RCBO which will add earth fault protection and maintain Overload protection for the PV circuit.
  • An ‘AC’ type RCD is not appropriate for this application and I should seek an RCBO with ‘A’ or ‘B’-type characteristics; I presume my installer will be able to advise on the exact type from OEM recommendations, but any thoughts on this from the experts?
  • The previous MCB move didn’t require a Minor Works Certificate as this wasn’t a new circuit or MCB. On that basis if this were to be replaced with an RCBO should I expect to receive a Minor Work Certificate (or other paperwork for my records)?

Thanks again for all of your times and wisdom.

Cheers,

Apologies for the bump, just one final call for help in case anyone more informed than me can advise on my assumptions/queries above, so that I know what to ask before I go back to my installer with a query...

 

Thanks in advance for any assistance!

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