The Value of R.C.D.s

I do think safety is a consideration and thus an RCD. Please refer to the post above and perhaps consider what it says. An installation disconnected as a whole with a double pole RCD is absolutely safe, it may have other problems but they are not electrically dangerous. A smart meter is no different from a single RCD, it disconnects the electrical installation for some reason, perhaps loading, but this is not considered dangerous. You will notice that smart Gas meters do not have this function, because turning off gas can be inherently dangerous.

I agree that its dangerouse to turn gas off without certain precautions before turnning it back on again  thats what the professionals say and thats good enough for me.  Now protecting a whole installation with a single up front RCD is not ideal in many ways putting g a whole house in darkness for a single fault dangerouse so if its possible to avoid it then its sensible to avoid doing that individual circuit RCBOs are far better  because at least you still have some power and also an idea of what area the fault us in. The advice and regulations given by the IET try to be best practice both in technical terms and from a safety of persons angle  so the two things are linked no doubt about it. 

I would hope most electricians would follow the guidance of GN1 on reg 314.1 on selection of types of RCD. 

If money and time were no object, we'd all have an RCBO for each socket, on an individual radial, probably wired in MICC and all DNO wiring would be TNS with big RCDs at the substation end. But that is not true.

So we have to ask how risky. It may actually be better for the customer's life expectancy to have a more dangerous wiring installation not updated, but use the money saved and get  the car tyres replaced instead. We cannot know in advance for any one person of course , but rather as throwing a bucket of coins, half of them come land ‘heads’ and half tails, we can talk in with confidence with the statistics of the large population and big numbers. Even in a bad year less than 50 folk a year are killed by domestic wiring installations and faulty appliances combined. 

See here for electrocution figures UK  as spreadsheet.

In the 1970s  it was perhaps half as much again.

Far more in fires https://www.gov.uk/government/collections/fire-statistics-monitor

So now it gets sticky - we need to assign a cost value to life - perhaps a million pounds per  life saved, perhaps a bit more for youngsters with a bright future ahead and and rather less for those if us  who are already partly time expired ?  (after all most of us will not last more than 3000Ms (100 years) even if all the wiring we see is perfect)

So if fitting an RCD costs £100, and it has a service life of perhaps 25 years, then on average every 10,000th RCD needs to save a life at least once over a 25 year period., or it was not worth it. That you can probably justify, so long as the other risks it introduces , of falling down the stairs in the dark or something do not undo the good. You also need the works doing to such a standard that the risk of a loose connection during the works causing a fatal fire is quite a bit less than 1 in 10000 as well, or you have lost all the advantage.

The advantage falls if the price goes up (say to a full consumer unit at a few K), or if the service life is shortened. Going the other way, if you could do the job for say ten pence, it would be a clear must-have, but you can't 

So RCDs are a good idea on new work. But the safety argument alone for a new consumer unit is  not justifiable until other factors drive it.

By simple mathematical analysis, we can show that applying the regs in this way is not about a balanced approach to safety.

Mike.

Colin Haggett: 
 

Maybe because it’s not good practice to always put a single RCD on the supply to a consumer unit? 

Is a single RCD for an entire home considered acceptable anyway? Regulation 531.3.2. Often standing “leakage current” of between 4 and 10 mA, but when appliances are switched on, a single RCD is likely to operate frequently. 

However, a split-load board with 2 RCDs would be OK for most domestic installations.

I would hope most electricians would follow the guidance of GN1 on reg 314.1 on selection of types of RCD. 

I guess this is the same point.

Colin Haggett: 
 

You might be very thankful of an RCD when you pick up the lawn mower cable you’ve just sliced in half. 

I have two words…. hedge trimmers… ? ?

davezawadi (David Stone): 
 

I do think safety is a consideration and thus an RCD. Please refer to the post above and perhaps consider what it says. An installation disconnected as a whole with a double pole RCD is absolutely safe, it may have other problems but they are not electrically dangerous. A smart meter is no different from a single RCD, it disconnects the electrical installation for some reason, perhaps loading, but this is not considered dangerous. You will notice that smart Gas meters do not have this function, because turning off gas can be inherently dangerous.

If anyone thinks “other problems” are OK … well, your insurer won't pay out for freezers full of food repeatedly … and then there's the point that protective devices are only specified for a finite number of operations.

Cost of a life?

It strikes me that the relaxation of covid restrictions is causing more deaths. The current rolling average in UK is 29 per day. It had been down to 6, so that's 23 excess deaths per day.

Let's assume that the relaxation leads to a recovery of GDP by 1%. Annual GDP = 500 Bn, = 1.4 Bn/day. That's about £60 million pounds of economic recovery per person, which seems to be a good cost-benefit ratio.

Now we ought to subtract the daily cost of hospital care. There are currently about 400 extra admissions per day. Assuming an average stay of 7 days at £2000 per day, that's a loss of £5.6 million.

Currently rolling average number of positive tests is 30,000. 14 days of self-isolation at the average wage of £500/week costs £30 million.

So the net gain in GDP looks pretty good.

Of course analysis of populations in this way is all well and good, but if you are the one who dies, that's a problem!

314.1 is often cited, but this is about individual circuits, not RCDs, and relates to faults in the Installation not particularly connected appliances.

Are you sure you don't have an out of date copy of BS 7671? In my copy 314.1 specifically talks not only about RCDs but also protective conductor currents ‘not due to a fault’ - which I presume is referring chiefly to leakage currents from appliances. 314.2 then talks about giving consideration to the consequences of the operation of any single protective device - not just overcurrent protective devices - so would seem to include RCDs too.

   - Andy.

davezawadi (David Stone): 
 

More what Z? Do you mean more doubt and uncertainty? In my experience, the only reason for any uncertainty is poor EICRs. I have seen many where the “Inspector” says that an RCD needs to be fitted without any specific information on the non-compliance, usually with a high quote for the work. There is zero data on how many people are “saved” by RCDs and going by the accident statistics there cannot be very many.

If an installation needs an RCD because of specific non-compliance then it seems that everyone wants to “Upgrade” the CU. This is not necessary or in many cases desirable. Why not just fit an RCD in the tails, job done in an hour and for £40 maximum for materials? 

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Z's Reply. Not a good idea as if the R.C.D. trips off everything is lost and that may introduce an additional risk. 132.1 (ii). and 361.1.

Z.

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But no that is apparently not good enough, and there is much hand waving. Almost immediately a new board full of RCBOs is “necessary”, for a cost of £600-£1000 at least, in Bristol anyway. Does this make the installation one tiny bit safer than a single RCD? It does not, so why is it apparently necessary? Then when you see the mess that is made trying to extend all the old wiring and trying to fit a new bigger board in a small space and even bonding all the pipework when this is not necessary, has anything improved at all?

Here is a good one too. An advert in a local ad magazine:

*** Electrical, NICEIC approved contractor and Domestic Installer. 

(I'm still not sure why you would be both, they are different in requirements)

Call in the Professionals

-Electrical Inspection Condition Reports (EICR)

Keep people safe with an inspection every 5 years

 

Would you trust that level of competence? They haven't even got the name right! The content will probably be equally imaginary.