For a standard domestic Install, split board with 2x Type AC main switches.
No PV or Car Chargers should this be a C3 or C2?
Thanks in advance
For a standard domestic Install, split board with 2x Type AC main switches.
No PV or Car Chargers should this be a C3 or C2?
Thanks in advance
Yesterday's announcement from the Government: https://www.gov.uk/government/news/government-to-go-further-and-faster-in-becoming-energy-secure
If plug-in PV is being pushed as a way forward, and these are to have a UK standard plug (although BS 1363-1:2023 Clause 5 states that the UK plug shall not be used for connecting generators) then certainly in rented homes, and in flats (rented or otherwise), for the installation to be considered safe, surely:
1. RCDs (RCCBs and RCBOs) for socket-outlet circuits (and upstream distribution circuits if applicable) would have to be at least Type A (because of the way inverters operate, but also for the existing PV inverter standard BS EN 62109-1, this is stated as a requirement for 'pluggable type A' equipment (i.e.. with a standard plug) to be compatible with Type A RCDs; and
2. RCDs (RCCBs and RCBOs) for socket-outlet circuits (and upstream distribution circuits if applicable) would have to be bidirectional (Regulation 530.3.201 introduced in Amendment 3); and
3. RCDs (RCCBs and RCBOs) for socket-outlet circuits would have to disconnect all live conductors (see Regulation 551.7.1)?
The simple fact is that MCBs, RCDs, RCBOs, etc. are unreliable devices which are not (in the domestic case at least) subject to any routine testing. Not being familiar with the product standards for these devices, I don't know what reliability requirements they are subject to, or indeed how compliance with any such requirements is demonstrated or monitored.
One might naively assume that the Wiring Regulations have been written with a full understanding of the reliability of these devices and somewhere in a dusty filing cabinet there is an assessment that says "yes, it is OK to use MCBs rather than fuses because whilst they have a much higher wrong side failure rate they have these benefits and here is a detailed risk assessment comparing the expected equivalent fatalities in comparison". A similar assessment would presumably exist for the use of RCDs and RCBOs which balances a slightly more relaxed approach to accidental contact against the possibility that the device will not operate. As an industry we would be negligent if such analyses didn't exist.
To return to this specific discussion, there will presumably be some form of quantitative assessment when looking at plug in solar which will attempt to balance the societal benefits of plug in solar against the fact that occasionally someone will be injured because of it (probably more likely to be from solar panels falling from high balconies rather than through shock but both need to be considered!).. Such an assessment would have to take account of the failure rate of whatever protective devices are included in the product. On the other hand, maybe my expectation is naïve and we will end up with a politician telling a civil servant to move whatever obstacles are preventing their use out of the way...
I note that the modern approach appears to be for manufacturers to lobby for the creation of a product standard so that they can avoid having to do all this safety stuff themselves and just blame the standard if things go wrong - perhaps I've swung too far from naivete to cynicism now...
The simple fact is that MCBs, RCDs, RCBOs, etc. are unreliable devices which are not (in the domestic case at least) subject to any routine testing. Not being familiar with the product standards for these devices, I don't know what reliability requirements they are subject to, or indeed how compliance with any such requirements is demonstrated or monitored.
They are type-tested. The tests include opening and closing the devices 2000 times and then checking for damage or undue wear.
MCBs rather than fuses
Fuses may be reliable, but replacing the wire is potentially hazardous and of course the terminals have to be tightened properly. Much easier to re-close an MCB/RCD (having identified and remedied the fault).
That type test doesn't give me any hint at all as to how many out of a population of (say) 10 million installed MCBs would actually open if subjected to an appropriate current. That information must surely be a key component in any argument as to why fuses are qualitatively worse. Similarly, I agree that rewireable fuses probably have a much higher failure rate than MCBs once human factors are considered, but those are not the only form of fuse which exists. To be clear I think MCBs are generally the right choice and they are generally sufficiently reliable for the applications we put them to.
Whilst I'm happy to engage in a MCB vs. fuses debate, my point was that many people rely on protective devices every day without really thinking about their reliability. We assume that they are "sufficiently" reliable and the Wiring Regulations back that up by permitting their use as best practice - that doesn't mean that things are "safe", it just means that sufficiently few people will be injured that no-one in a position of power will worry about it. That "sufficiently few" test varies over time in tune with popular sentiment.
Plug in solar will need to meet the same test - if it is to succeed it will need to injure sufficiently few people that overall the population thinks it is a good idea.
As I alluded to in my post, I suspect there may be more risks from insufficiently secure panels causing impact injuries than from faulty RCDs (it isn't clear to me how a RCD helps in the one finger touches the live pin on the plug, another touches the neutral pin case anyway) but that is not to say that we shouldn't be making the electrical side as safe as possible. For me, the big debate is balancing the generation standards which tend to favour slow disconnection of generators in the face of network disturbance with safety standards in a domestic setting which favour rapid disconnection. If we think that plug in solar will only ever make up a tiny amount of the grid's generation mix then the answer is obvious and we can specify inverter shutdown / disconnection times of the same order of magnitude as RCD trip times but if widespread adoption is expected then the discussion is more complex.
Just for clarity, the RCD part of a unidirectional RCBO may fail in such circumstances but will the mcb characteristic remain available?
Does that always matter, for example is the RCD is used for ADS due to circuit length, or in cases such as socket-outlet circuits where additional protection is necessary to meet the requirements for ADS in BS 7671?
One interesting question is why can't we (I) tell if my recent trip of a circuit with RCBO protection was because of overload, or a nuisance leakage scenario?
Because we don't know, we can't explain, and aren't sure if it should have tripped in another scenario.
Is there any evidence that RCDs have saved lives over the past 40 - 50 years?
It has certainly been stated in expert evidence that RCD could have saved a life if one had been fitted.
And anecdotally if not saved , certainly less badly burnt.
I for example have been disconnected by 30mA RCD, just once ,and was very grateful for it, but still painfully shaken. I have also been saved by the prompt action of a colleague, on something that had no RCDs, but that left my hands with lovely entry and exit wounds that took weeks to heal. Both were very close calls, and once (twice?) in a lifetime events that required many things to have gone wrong so unlikely, and that is for one who gets stuck in more than the average member of the public.
Equally there must be millions of RCDs that are never called upon to trip in anger during their whole operational life (and of those that are, as above a small % wont..)
If we assume my life is worth £1Million (!) then that justifies the cost of fitting about 50K RCDs at say £20 each on new circuits to save me once.
To call someone out to do a replacement, and certainly if that involves a new CU, is probably ten times more expensive, now unless someone gets saved once per 5000 RCDs installed, it is a net loss. We have less than 100 electrocutions per year (*), which is a chance of somewhere between one and two per million, per year, per person.
As such the argument for the additional cost vs benefit on new circuits is reasonably in favour, but the argument for "must retrofit" to existing is probably rather weak.
Mike
** Actually a lot of those electrocutions are touching overhead lines with vehicles and poles, and there is no number of additional domestic RCDs that would help with that so maybe more like less than 1 per million. But there is an additional reduction in fires and so on to offset that a bit.
If we assume my life is worth £1Million (!) then that justifies the cost of fitting about 50K RCDs at say £20 each on new circuits to save me once.
It isn't quite that simple. You really need to do a number needed to treat analysis. The difficulty is that electrocution is (mercifully) rare.
Let us suppose that the death rate from electricity is 1 in a million = 10-6 = 10 x 10-7. We have a new gizmo, which reduces the mortality by half, so 5 x 10-7. Absolute risk reduction is (10 x 10-7) - (5 x 10-7) = 5 x 10-7. NNT = 1/ARR = 2 x 106.
So 2 million new gizmos have to be fitted to save one life.
It has certainly been stated in expert evidence that RCD could have saved a life if one had been fitted.
As I stated earlier.
Considering the time it take to write/publish a BS like BS7671 the lifecycle should start to consider the recommendation of of type B as a minimum for BS7671 Ammendment 5 or 19th edition. Ideal for EV chargers, solar PV (inverters). Caveat could be if it a new design or retrofit
Lets not forget the type F as well for inverter driven loads like washing machines and heat pumps.
I am sure that will be an interesting debate for the JPEL Team for UK Domestic Dwellings
As always there is a grey area
What is recommended/mandated for a New Design
What coding is given on an EICR or In Service inspection and testing. This could be 3,5 or even 10 years after initial install depending on usage. If for homeowner usage it could be 10 to 20 years or untill the sell the property. if the property is PRS (Private Rental Sector) then EIC and EICR are needed from day 1 of the rental agreement. In effect theis makes a 2 tear system. Rented dwellings are more upto date (BS7671) than owner/occupied dwellings.
I am sure you family would rather pay £10 per RCBO in the CU and have you still there and very much alive. The £1Million value is just what bank and insurance companies use to quantify a life. Your family would say your life is worth way more than that and may even be priceless.
I am sure you family would rather pay £10 per RCBO in the CU and have you still there and very much alive. The £1Million value is just what bank and insurance companies use to quantify a life. Your family would say your life is worth way more than that and may even be priceless.
I am sure you family would rather pay £10 per RCBO in the CU and have you still there and very much alive.
That may indeed be true or not, and they don't know it but they already have paid for some RCBOs in our home CU. However they are not going to want to pay for lots of RCDs that never get called on to do anything in properties that none of us will ever visit, especially if it takes money from other safety activities like putting winter tyres on the car or boiler checks.. And more generally is not wise to ask family members to estimate your value, as it may be less than that megapound.
Mike
I am sure you family would rather pay £10 per RCBO in the CU and have you still there and very much alive.
What a kind assumption! :-)
Whether the RCD failure rate be 3% or 7%, I'd like to know whether the more expensive brands are more reliable. By and large, I think that a free market decides the question, but I really do not know. £1k SP DBs do exist - are they worth it?
I think that a free market decides the question,
In these areas of safety, the market is rarely able to decide. Placebos are a lot cheaper, and value is difficult to determine.
Second hand car sales has a similar value-price-consequence problem.
I'd like to know whether the more expensive brands are more reliable.
Brands set their testing percentage at point of manufacture. Some like Hager test about 5 to 15% of the RCBO they make, Some cheap imports made in China test less than 1%. Other brands like Navitascp do a far batter job and test every RCBO before shipping. On top of that they are a UK company.
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