240v from Sink

[JohnW2]

My recollections are that RCDs save lives by reducing the number of dangerous, potentailly fatal, situations by tripping before a person comes in contact with a Live item.

That obviously could happen, but I'm not sure how common these 'non-negligible-impedance' faults actually are. The fault would have to have an impedance of 'a good few ohms' to prevent an MCB tripping within an hour or so - and one would very very unlucky to touch the part (and something else) during that hour!

Whatever, even though that mechansim has the potential to 'save lives', whether or not it actually has saved an appreciable number of lives by that mechanism is a different matter. There certainly has not be a marked reduction in recorded domestic electrocutions in the period during which RCDs have moved from being 'rare/unknown' to 'pretty ubiquitous'.

It is said ( by fire protection officer ) that RCDs reduce the number of fires ignited by electrical faults ( Live to Earth via a resistive short that heats up will trip the RCD before ignition temeperature is reached )

That, of course, is even more intangible, and almost impossible to quantify. Again, I have to wonder how common it is to get a fault which results in high enough temperatures to start a fire without an OPD operating fairly quickly. Furthermore, on the very rare occasions I have experienced a fault in an appliance/equipment which has caused high currents to flow, it has most commonly been due to a L-N fault (which caused an OPD to operate), so an RCD would not have helped.

Don't get me wrong. I'm a great believer in RCDs (as an extra protection against the 'very unlikley'), having been using them (for virtually all circuits) since long before there was any regulatory requirement to have them. I'm just uncertain as to how many lives they have actually saved, or serious injuries they have prevented.

Kind Regards, John

 

[JohnW2]

Sorry my point was inaccurate and muddled, what I should have said is an RCD doesn't make things safe, the circuit is supposed to be safe from basic protection and then disconnection time from short circuits as they were before RCDs became common place.

Fair enough. That's obviously all true, for a TN installation (assuming that the 'short circuits' you mention are L-E ones).

In my mind the RCD would more often detect faults not of negligible impudence, which was a big gap in the previous editions of the regs ....

Before we had RCDs (or, at least, VOELBs) there was, of course, no way of detecting/terminating a fault which was not 'of neglible impedance'. You may be right but, as I've just written to bernard, I'm not sure how common these postulated L-E faults with impedances of a good few ohms actually are.

... but clearly in the less likely case of direct contact, the consequences would be worse without an RCD.

As I've said ... "possibly".

I think more RCD trips have been from circuit faults than current flowing through a person ...

Undoubtedly - but in many of those cases an OPD would probably have operated if an RCD had not been present. In practice, I imagine that the great majority of RCD trips are either 'nuisance' (sporadic and no cause ever found) or else are due to people working on an SP-isolated circuit and touching N and E together (and at least that 'exercises' the RCD )!

Kind Regards, John
Edit: typo corrected (thanks to EFLI)

 

[John D v2.0]

Interesting thread, thanks all!

 

[EFLImpudence]

people working on an SP-isolated circuit and touching L and E together (and at least that 'exercises' the RCD )!

Typo? Did you mean N and E.

 

[JohnW2]

Typo? Did you mean N and E.

I did . Thanks for pointing that out, I'll correct it!

Kind Regards, John

 

[jg321]

In practice, I imagine that the great majority of RCD trips are either 'nuisance' (sporadic and no cause ever found) or else are due to people working on an SP-isolated circuit and touching N and E together (and at least that 'exercises' the RCD )

Been there, done that, in my previous property, where the RCD was being used as the main switch. In a room with no windows, at night, when I'd just moved in (so didn't instinctively know my way back to the CU).

In fact, googling as to why that happened (having been used to working on non-RCD supplies over the years and N-E contact never being an issue), is likely what made me discover this forum (so RCDs do have something to show for themselves in this regard at least!).

I'll never forget my girlfriend shouting "Jon, was that meant to happen?!" from the pitch dark lounge!

Jon

Edit to add: Incidentally, after living in RCD protected properties for around 10 years, I've never experienced a nuisance trip, or indeed a trip other than that mentioned above, or me pressing the "test" button when I move in!

 

[JohnW2]

Edit to add: Incidentally, after living in RCD protected properties for around 10 years, I've never experienced a nuisance trip, or indeed a trip other than that mentioned above, or me pressing the "test" button when I move in!

Similar here. I've been living with many RCDs (probably about a dozen) for ~20years and have experienced virtually no 'nuisance' (unexplained) trips. However, it's clear from seeing what some people say and write that there are those who are much more 'unlucky'.

Kind Regards, John

 

[bernardgreen]

after living in RCD protected properties for around 10 years, I've never experienced a nuisance trip,

For me it is more than 30 years and counting.

 

[John D v2.0]

Edit to add: Incidentally, after living in RCD protected properties for around 10 years, I've never experienced a nuisance trip, or indeed a trip other than that mentioned above, or me pressing the "test" button when I move in!

Although there should be a sticker on your cu telling you to "test" the RCD every 3 months. Actually it's not specifically to check it's working it's also to exercise it to stop it seizing up/getting slow.
Although you'd struggle to find people who do that in the real world.

 

[JohnW2]

Although there should be a sticker on your cu telling you to "test" the RCD every 3 months. Actually it's not specifically to check it's working it's also to exercise it to stop it seizing up/getting slow.

Indeed - it fulfills both functions.

Although you'd struggle to find people who do that in the real world.

One of my daughters used to religiously test her RCDs very regularly. Unfortunately, she has moved into a "never again" frame of mind - and I suppose one can't blame her (even though I've attempted to reassure her that what she experienced is incredibly rare!) - (click here to learn what she experienced, and why) !

Kind Regards, John