live to earth short circuit tripped mcb but not rcd?

[333rocky333]

Pressing the test button, how much current would pass through an Rcd, is it a standard value.
Surely the Test button tests the unit, though granted it cannot test the Operation speed

Is it possible for a devices test button to work , but the unit not trip with a L to E fault under normal circumstances, don't most Rcds Fail because they trip too slow rather than not trip at all.
I have encountered the reverse problem, where Trip button fails, but Rcd tests ok, but take it that was more Trip Mechanism failure responsible.

 

[Taylortwocities]

@jim63 Your RCD should have a label near it that says this.

Note the bit about using the test button quarterly. Have you been doing that.
RCDs are known to get a bit stuck if they aren't exercised for a long time (hint)...

 

[JohnW2]

Pressing the test button, how much current would pass through an Rcd, is it a standard value.

We've discussed that before and, if I recall correctly, I think it seems (on the basis of the value of resistors people have found in dissected ones) around double the IΔn (i.e. around ~60mA for a 30mA device).

Kind Regards, John

 

[jim63]

@jim63 Your RCD should have a label near it that says this.
View attachment 149440

Note the bit about using the test button quarterly. Have you been doing that.
RCDs are known to get a bit stuck if they aren't exercised for a long time (hint)...

Like most people, I have never really bothered to test the rcd monthly, I don't know anyone who does? The rcd has tripped in the past where there has been a faulty iron, and sometimes when I accidentally touched neutral to earth when replacing sockets, although touching neutral and earth didn't always trip the rcd, I'm sure it saved my life years ago from a very powerful shock, I can still remember the huge sensation running up arm through my body and my head feeling funny as if I was going to pass out, the shock was only for a brief second but very intense then the rcd cut the power. You'd think I'd learn my lesson by now by switching the power off before loosening accessories even if you are not necessarily going to touch the terminals.

 

[Taylortwocities]

Personally, I would have the RCD tested, to be sure it is operating to spec.

 

[333rocky333]

@jim63 Your RCD should have a label near it that says this.
View attachment 149440

Note the bit about using the test button quarterly. Have you been doing that.
RCDs are known to get a bit stuck if they aren't exercised for a long time (hint)...

Never realised till now, the new 18th regs has changed the label to test 6 monthly.

 

[JohnW2]

Never realised till now, the new 18th regs has changed the label to test 6 monthly.

How odd - I hadn't noticed, either. The result of that will presumably be an increase the number of people who do not remember to test at all.

Kind Regards, John

 

[333rocky333]

...

 

[Risteard]

How odd - I hadn't noticed, either. The result of that will presumably be an increase the number of people who do not remember to test at all.

Kind Regards, John

I was aware of the change.

I would suggest it could actually help in that (like in many other places) it can now be suggested to test when the clocks change (as they will need reset anyway).

 

[JohnW2]

I would suggest it could actually help in that (like in many other places) it can now be suggested to test when the clocks change (as they will need reset anyway).

Good point - I hadn't thought of that way of getting a 'cue'/ reminder. Mind you, for those who get quarterly electricity bills, it could be suggested that appearance of such a bill would be a very apposite cue that a 3-monthly test was due!

In the absence of any such cues, remembering to do things regularly tends to get worse with increasing intervals. That's certainly true in terms of taking medicines. Even though one might think that 'the weekend' was a fairly good cue, compliance in taking tablets 'once per week' is usually far worse than with 'once per day'.

Kind Regards, John

 

[Risteard]

Good point - I hadn't thought of that way of getting a 'cue'/ reminder. Mind you, for those who get quarterly electricity bills, it could be suggested that appearance of such a bill would be a very apposite cue that a 3-monthly test was due!

In the absence of any such cues, remembering to do things regularly tends to get worse with increasing intervals. That's certainly true in terms of taking medicines. Even though one might think that 'the weekend' was a fairly good cue, compliance in taking tablets 'once per week' is usually far worse than with 'once per day'.

Kind Regards, John

Indeed. I suppose there is never any guarantee that people will do what you instruct them, even if it has been made clear to them that it is for their own good/safety.

 

[JohnW2]

Indeed. I suppose there is never any guarantee that people will do what you instruct them, even if it has been made clear to them that it is for their own good/safety.

True, but it's not necessarily a deliberate failure to follow instructions - it's often simply a case of failings of memory. If you told people they had to test their RCD every day, or every week, at least a few might actually find that easier than 3-monthly or 6-monthly!

Kind Regards, John

 

[ericmark]

MCB tripping time 1/2 cycle = 10 mS, RCD tripping time 2 cycles = 40 mS so the MCB should trip first.

 

[JohnW2]

MCB tripping time 1/2 cycle = 10 mS, RCD tripping time 2 cycles = 40 mS so the MCB should trip first.

I'm not sure to what extent one can rely on tripping times in 'cycles', since many of the factors determining disconnection time are 'mechanical' in nature, and therefore unrelated to anything electrical.

In any event, a device will probably 'pass the point of mechanical no-return' fairly early in the tripping process. Hence, even if the figures above were correct, whilst it should mean that the MCB would 'trip first', if the RCD had passed it's 'point of no return' in the first 10 ms, it would also trip - albeit not completing its trip process until up to 30 ms later than the MCB.

Kind Regards, John

 

[jim63]

Hello again, having done further inspection, it turns out if I touch the neutral and earth together the rcd does not trip at all, I tell a lie it does trip but only when heavy loads are switched on such as the kettle, Do I have an earthing or insulation problem? I heard somewhere that a nicked neutral somewhere can cause an rcd to become less sensitive due to a slight capacitance in its coil or something along those lines. does this sound likely? I have pressed the test button on the rcd on a daily basis now and it trips every time, so I'm not sure if it is faulty, Could I have a pinched neutral conductor somewhere or a broken earth somewhere, or is it something more sinister? My main concern now is the rcd may not trip if someone was to receive an electric shock.
Am I worrying over nothing, could it be there is just not enough leakage on the system? the rcd does seem to be less sensitive as it was before. The rcd in question is roughly 20 years old, but I would think if it was faulty it would be more sensitive not the reverse.
thanks