phil d
Well-known member
What is the point of the RCD? I ask this in the hope of instigating an intelligent debate, recently there was a post on a forum somewhere about an issue with an RCD under test. The chap had tested an RCD, by plugging his tester into a socket outlet and the RCD had failed to trip within the required time. He had tested at the device's outgoing terminals (load disconnected) as per GN3 and it tripped within the time required.
He was querying whether this device should remain in service, I said that I would be unhappy if it didn't trip at the "point of use" and therefore be inclined, in the absence of any other reason for it not to trip at the socket to replace it. My argument being that I would not like to have to stand up in court and state "yes your honour, I'm aware of the fact that the RCD didn't trip when tested at the socket, but it did at the board" . It seems pointless having a device that is widely regarded as a safety device if it doesn't work at the point it's needed, Imagine fitting a car with airbags then saying, "oh by the way, they won't deploy in a crash if you have the radio on, or the wipers working".
Most domestic installations require RCD protection as more often than not the method of installing the cables doesn't meet the criteria for not requiring RCD's, depth of cables, construction of wiring system etc. Now we are all aware of what the requirements are, so I'm not going to go into them here, however I would like to throw the following open to debate and see what we come up with, I'm not trying to prove who's cleverer than who or who knows the regs better than who, that's not the point of this, it is merely the point listed below.
Now as far as I'm aware the only requirement of an RCD when being tested is, that it must trip within the stated time for the particular device rating, there is no mention of or indeed requirement to record an actual measured tripping current on the test sheet, in fact there is not even a place to record it. Also afaik there is nowhere that states an RCD must trip when the test is performed at a socket outlet, in fact GN3 tells you to perform the test at the device itself. So if the only concern is whether the device trips at it's terminals then what is the point of fitting them? We are told that if we fit a normal ring final in an ordinary house in the normal way, I.E 2.5 t&e in capping beneath plaster, then that circuit must be protected by an RCD. This we are told is to afford protection in the event somebody drives a nail into the cable for example, now if there is no requirement to test said device for correct operation at some point on said circuit, and even worse that we are told that provided the device trips when tested at it's terminals then it is fine, subject to meeting the required trip times then what is the point of the device? If it doesn't trip when tested at a socket then how do we know it will trip if somebody drives a nail into the cable it is "protecting" , we don't do we? There was also a comment made by someone that "certain devices can affect the tripping of RCD's when they are on the same circuit", does that again not come back to my "airbags and wipers" analogy?
As I said guy's I don't want this to turn into a points scoring exercise, or for anyone to start having a go at anyone, re their interpretation of the regs, what my point is, is given the way things are worded, note I said worded, not interpreted, what exactly is the point of the RCD?
He was querying whether this device should remain in service, I said that I would be unhappy if it didn't trip at the "point of use" and therefore be inclined, in the absence of any other reason for it not to trip at the socket to replace it. My argument being that I would not like to have to stand up in court and state "yes your honour, I'm aware of the fact that the RCD didn't trip when tested at the socket, but it did at the board" . It seems pointless having a device that is widely regarded as a safety device if it doesn't work at the point it's needed, Imagine fitting a car with airbags then saying, "oh by the way, they won't deploy in a crash if you have the radio on, or the wipers working".
Most domestic installations require RCD protection as more often than not the method of installing the cables doesn't meet the criteria for not requiring RCD's, depth of cables, construction of wiring system etc. Now we are all aware of what the requirements are, so I'm not going to go into them here, however I would like to throw the following open to debate and see what we come up with, I'm not trying to prove who's cleverer than who or who knows the regs better than who, that's not the point of this, it is merely the point listed below.
Now as far as I'm aware the only requirement of an RCD when being tested is, that it must trip within the stated time for the particular device rating, there is no mention of or indeed requirement to record an actual measured tripping current on the test sheet, in fact there is not even a place to record it. Also afaik there is nowhere that states an RCD must trip when the test is performed at a socket outlet, in fact GN3 tells you to perform the test at the device itself. So if the only concern is whether the device trips at it's terminals then what is the point of fitting them? We are told that if we fit a normal ring final in an ordinary house in the normal way, I.E 2.5 t&e in capping beneath plaster, then that circuit must be protected by an RCD. This we are told is to afford protection in the event somebody drives a nail into the cable for example, now if there is no requirement to test said device for correct operation at some point on said circuit, and even worse that we are told that provided the device trips when tested at it's terminals then it is fine, subject to meeting the required trip times then what is the point of the device? If it doesn't trip when tested at a socket then how do we know it will trip if somebody drives a nail into the cable it is "protecting" , we don't do we? There was also a comment made by someone that "certain devices can affect the tripping of RCD's when they are on the same circuit", does that again not come back to my "airbags and wipers" analogy?
As I said guy's I don't want this to turn into a points scoring exercise, or for anyone to start having a go at anyone, re their interpretation of the regs, what my point is, is given the way things are worded, note I said worded, not interpreted, what exactly is the point of the RCD?
