The Value of R.C.D.s

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.

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.