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 average consumer will have no idea what sort of RCDs they have.
Neither will yer average politician.
They will be happy until something does happen, it's put forward that the RCD didn't operate and that might have saved a life ... and then all hell will break loose; and it will, of course, be our fault !
Given that in-service RCDs have a general failure rate something in the order of 7% ... aren't we in that situation anyway?
Likewise when the householder admits they haven't pressed the T button in the last 6 months...
- Andy.
Given that in-service RCDs have a general failure rate something in the order of 7% ...
Are we sure this statistic still current? Yes, I'm aware that, what is now quite a long time ago, there was a study that indicated that statistic ... but there have been a number of developments in product standards for RCDs over the past 25-30 years.
In fact, this site proposes 97 % reliable, with an improvement if the devices are tested regularly: https://www.electricalsafetyfirst.org.uk/guidance/safety-around-the-home/rcds-explained/
Compare that with certain unidirectional devices that are known to fail 100 % of the time if they are operated (including by pressing the test button) with a 230 V source connected to the load terminals ...
aren't we in that situation anyway?
So, no I don't think we are.
In fact, this site proposes 97 % reliable, with an improvement if the devices are tested
I really struggle with that. I suppose that it means that if RCDs are tested and are found to fail, they are replaced, which apparently improves the reliability overall.
3% failure rate. What would you accept for the brakes on your car, for example?
What would you accept for the brakes on your car, for example?
Surely there are far more [orders of magnitude more] injuries and deaths due to RTAs than electricity-related incidents?
Need I say more?
In fact, this site proposes 97 % reliable,
OK maybe 3% rather rather than 7% .. but the same point remains I think - we're already in a situation where an RCD may well not save a life when it was expected to. Someone may be called up to explain. The explanation may be entirely reasonable - nothing's 100% perfect - we do the best we can with the technology available and the limits of acceptable costs - the victim was part of the unfortunate 5% or so of the population that isn't fully protected by electrical theory, etc.
Ultimately is it worth upgrading probably millions of RCDs at a national cost of hundreds of millions if not billions of pounds, to achieve, not perfection, but merely something slightly less imperfect? Or would the money be better spent on some better returning safety measures?
- Andy.
Surely there are far more [orders of magnitude more] injuries and deaths due to RTAs than electricity-related incidents?
OK, bad analogy.
How about seatbelts? In the vast majority of journeys, they provide no restraint because none is required.
Is there any evidence that RCDs have saved lives over the past 40 - 50 years? Even if electrical fatalities have reduced, it could be for other reasons, so difficult to prove.
Compare that with certain unidirectional devices that are known to fail 100 % of the time if they are operated (including by pressing the test button) with a 230 V source connected to the load terminals ...
Just for clarity, the RCD part of a unidirectional RCBO may fail in such circumstances but will the mcb characteristic remain available?
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).
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.
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