Price idea please

[bernardgreen]

the previous owner did fit an unnecessary RCD FCU.

and then finding it unnecessary removed it.

( it is be kind to Winston hour here )

 

[JohnW2]

the previous owner did fit an unnecessary RCD FCU.

and then finding it unnecessary removed it. ( it is be kind to Winston hour here )

More seriously, as I've just written in another thread, this "unnecessary" is, IMO, open to some debate. IF one believes that RCDs are worthwhile (to protect life and limb), and IF one believes that the in-service failure rate of RCDs is anything like as high as some reports suggest, then there would be a pretty strong case for having two (or more!) in series.

If I thought that there was anything remotely like a 7% chance that the seatbelt or airbags in my car would fail to function satisfactorily if/when 'needed in anger', then I would certainly want some secondary (if not also tertiary!) back-up systems in place!

Kind Regards, John

 

[AndyPRK]

I'm with you John until the reports I've heard on here about the rcd fcu's smoking. I think this worries me more. Maybe that's rare too.

 

[JohnW2]

I'm with you John until the reports I've heard on here about the rcd fcu's smoking. I think this worries me more. Maybe that's rare too.

Fair enough, but if RCD FCUs are 'smoking', that's presumably due to a design and/or manufacturing problem (which would clearly need to be resolved/rectified), and does not alter the concept of what I was saying.

Kind Regards, John

 

[333rocky333]

More seriously, as I've just written in another thread, this "unnecessary" is, IMO, open to some debate. IF one believes that RCDs are worthwhile (to protect life and limb), and IF one believes that the in-service failure rate of RCDs is anything like as high as some reports suggest, then there would be a pretty strong case for having two (or more!) in series.

Though a lot of these fcu's and sockets use a dual button for off and test, it could be a pain if you trip the circuit every time you turn it off, though i see your point.
I wonder how much faster, if at all an rcd located near an appliance would operate in a fault as opposed to one in the board, 10 metres away.
Your good at maths john

 

[JohnW2]

Though a lot of these fcu's and sockets use a dual button for off and test, it could be a pain if you trip the circuit every time you turn it off, though i see your point.

It would be a pain, but does it actually happen? Whatever, my point was a general one about the possible wisdom of having two (or more!) RCDs in series - the problem to which you refer could be eliminated by using RCDs sockets/FCUs etc. which had proper functional switches.

I wonder how much faster, if at all an rcd located near an appliance would operate in a fault as opposed to one in the board, 10 metres away. Your good at maths john

As I'm sure you understand, it's not really worth doing any maths - current in a cable 'travels' at a speed approaching the speed of light, so I presume that L-N imbalances will become apparent to a distant RCD roughly that quickly. Light travels at roughly 300,000,000 metres per second (electricity in a cable perhaps about half of that), so you could do the sum yourself (for 10 metres) if you really thought it would be worthwhile

Kind Regards, John

 

[ekmdgrf]

As I'm sure you understand, it's not really worth doing any maths - current in a cable 'travels' at a speed approaching the speed of light, so I presume that L-N imbalances will become apparent to a distant RCD roughly that quickly. Light travels at roughly 300,000,000 metres per second (electricity in a cable perhaps about half of that), so you could do the sum yourself (for 10 metres) if you really thought it would be worthwhile

Isn't it more of a Newton's Cradle effect? So you stick an electron on one end of the cable and one drops off the other end? So you're not really waiting for an electron to travel the length of the cable at 150,000Km/s or whatever the speed of light in copper is.

Of course, this gives rise to another of my hair brain ideas: if we could get the electrons to exceed the speed of light in Copper, we could turn the wire into a nice, gentle, blue strip light. Great for lighting the bathroom in the small hours.

 

[JohnW2]

Isn't it more of a Newton's Cradle effect? So you stick an electron on one end of the cable and one drops off the other end? So you're not really waiting for an electron to travel the length of the cable at 150,000Km/s or whatever the speed of light in copper is.

As you imply, it's nothing to do with the speed of movement of electrons, which is very slow.

However, nor is it an 'instant' phenomenon (i.e. one electron does not drop off the other end the very instant that one is 'stuck in' to the other end. It's similar to the situation in which one is attempting to 'communicate' by pulling on a very long piece of string, or by pushing/pulling a very long stick. When one initiates a movement at one end of the string/stick, it propagates to the other end as a 'wave', which travels at finite speed, and it hence takes a finite time before one's movement of one end of the string/stick shows itself at the other end. In the case of electricity, it's an electromagnetic wave, and that travels at whatever is the 'speed of light' in the medium/media concerned (and don't forget that the wave extends outside, as well as inside, the electrical conductor concerned).

Kind Regards, John