Indeed. Nor even <30mph! The threshold is 30mph, and the criterion for 'being legal' is ≤30mph.
Kind Regards, John
Contact voltage on PE-conductor
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Kind Regards, John
And the threshold for the device indicating danger is < 35V.
I suspect bad translation/clumsy expression of concept is to blame.
I suspect that what they are trying to say is that the threshold which, if crossed, would flag an alarm is somewhere below 35V, but exactly where they cannot predict, all they know is that it will never be 35V or more.
But to be sure, clarification from the maker should be sought. One of my installation testers (also German) has the same feature - I'll try to remember to dig out the manual and see how it describes it.
I suspect bad translation/clumsy expression of concept is to blame.
I suspect that what they are trying to say is that the threshold which, if crossed, would flag an alarm is somewhere below 35V, but exactly where they cannot predict, all they know is that it will never be 35V or more.
But to be sure, clarification from the maker should be sought. One of my installation testers (also German) has the same feature - I'll try to remember to dig out the manual and see how it describes it.
... which seems to be an echo of ...
The more I think about it, the more it seems to me that (whatever the 'threshold') the "contact potential test" functionality of the Schneider IMT23003 has to be a bit 'iffy', in the sense of being unreliable, hence potentially misleading and even potentially 'dangerous', if too much is read into the results it gives.
After all, it surely has to be just a variation on the theme of a 'neon test screwdriver' and, worse than that, a neon screwdriver being used to confirm the absence of a dangerous voltage - in effect, 'testing for dead', but presumably with a lower voltage detection threshold than a neon-test-screwdriver.
The voltage-sensing circuitry will have a finite 'input resistance/impedance', and there will have to be a very high value resistor in series with the 'touch button' (for safety reasons). However, since both those resistances/impedances are known, that can be taken into account, so one can easily design sensing circuitry that would give an indication if the pd between CPC and the body of the person touching the test 'button' was above some (precisely specified) threshold.
However, that's about it. The device can accurately give an indication of the pd between CPC and the user's body, but nothing can be known about the potential of their body relative to earth. That will be dependent upon the effective impedance of the coupling between that person's body and true earth - which, during the test, will form a potential divider between CPC and true earth (one part of the divider being that impedance plus the 'safety resistor' and the other part being the input resistance/impedance of the sensing circuitry).
Hence, just as with a neon screwdriver, it is possible for it not to 'indicate', despite a substantial PD between the 'test point' (CPC) and true earth, if the coupling between the user's body and true earth is poor (high impedance).
In a literal sense, I suppose it does what it says on the tin - determines whether the 'touch voltage', when a particular person in a particular place and position on a particular day (who is not touching anything else relevant) touches a CPC (or nearby exposed-c-p), but it could 'pass' that test and yet would still leave a person in danger if they simultaneously touched CPC/exposed-c-p and something closer to true earth potential (i.e. in the presence of a 'faulty' equipotential zone, which is really the risk we are talking about).
I would personally regard this as just being a 'slightly better' version of a neon screwdriver being applied to a CPC or exposed-c-p to confirm that it was 'dead' - I say 'slightly better' in the sense that the threshold could be set at anything one liked (e.g. 35V), whereas a neon screwdriver's 'threshold' will be dictated by the striking voltage of the neon, probably around 90V - but, apart from that, I see little difference.
Am I wrong in thinking like this?
Kind Regards, John
After all, it surely has to be just a variation on the theme of a 'neon test screwdriver' and, worse than that, a neon screwdriver being used to confirm the absence of a dangerous voltage - in effect, 'testing for dead', but presumably with a lower voltage detection threshold than a neon-test-screwdriver.
The voltage-sensing circuitry will have a finite 'input resistance/impedance', and there will have to be a very high value resistor in series with the 'touch button' (for safety reasons). However, since both those resistances/impedances are known, that can be taken into account, so one can easily design sensing circuitry that would give an indication if the pd between CPC and the body of the person touching the test 'button' was above some (precisely specified) threshold.
However, that's about it. The device can accurately give an indication of the pd between CPC and the user's body, but nothing can be known about the potential of their body relative to earth. That will be dependent upon the effective impedance of the coupling between that person's body and true earth - which, during the test, will form a potential divider between CPC and true earth (one part of the divider being that impedance plus the 'safety resistor' and the other part being the input resistance/impedance of the sensing circuitry).
Hence, just as with a neon screwdriver, it is possible for it not to 'indicate', despite a substantial PD between the 'test point' (CPC) and true earth, if the coupling between the user's body and true earth is poor (high impedance).
In a literal sense, I suppose it does what it says on the tin - determines whether the 'touch voltage', when a particular person in a particular place and position on a particular day (who is not touching anything else relevant) touches a CPC (or nearby exposed-c-p), but it could 'pass' that test and yet would still leave a person in danger if they simultaneously touched CPC/exposed-c-p and something closer to true earth potential (i.e. in the presence of a 'faulty' equipotential zone, which is really the risk we are talking about).
I would personally regard this as just being a 'slightly better' version of a neon screwdriver being applied to a CPC or exposed-c-p to confirm that it was 'dead' - I say 'slightly better' in the sense that the threshold could be set at anything one liked (e.g. 35V), whereas a neon screwdriver's 'threshold' will be dictated by the striking voltage of the neon, probably around 90V - but, apart from that, I see little difference.
Am I wrong in thinking like this?
Kind Regards, John
Maybe you are over-thinking it.
As long as they caution people not to rely on it, and not assume that lack of an indication equals lack of a problem, then even if it only "works" some of the time, that has to be better than having nothing, which is clearly "works none of the time".
False positives might cause unnecessary worry and expense, but that's about it.
I don't know what the gubbins inside does, but they are in a position to know if the cpc appears to be present, so could leave the button unconnected if not, but in any event touching it would be no more dangerous than touching an earthed exposed-conductive-part of any accessory or appliance in the same installation. If the plug-in tester had an earthed metal body, would you shy away from using it?
As long as they caution people not to rely on it, and not assume that lack of an indication equals lack of a problem, then even if it only "works" some of the time, that has to be better than having nothing, which is clearly "works none of the time".
False positives might cause unnecessary worry and expense, but that's about it.
Would there?
I don't know what the gubbins inside does, but they are in a position to know if the cpc appears to be present, so could leave the button unconnected if not, but in any event touching it would be no more dangerous than touching an earthed exposed-conductive-part of any accessory or appliance in the same installation. If the plug-in tester had an earthed metal body, would you shy away from using it?
Put another way ... if someone had some reason to think that some exposed-c-p might possibly be at a dangerous potential, would we be happy to suggest that they applied a neon screwdriver to it in order to 'confirm' that it was 'safe'?
Kind Regards, John
Kind Regards, John
Put it another way ... would we suggest that nobody ever touched an exposed-c-p in case it might possibly be at a dangerous potential?
Put it another way ... if someone made a plug in tester like this, and to make it nice and robust used a metal case, which was earthed, would you refuse to plug it in unless wearing rubber gloves?
Put it another way ... when you encounter metal accessories, do you refuse to operate them unless wearing rubber gloves?
This device is not to test for the presence of a risk which would not be a risk to anybody if they didn't use it to test for it. It is to alert people to the presence of a risk to which they are exposed, whether they know it or not, every time they clap hands on an exposed-conductive part.
If there is a fault, then using this tester does not make life an iota more dangerous. But it might lead to it being a great deal safer. Ignorance is not always bliss.
Put it another way ... if someone made a plug in tester like this, and to make it nice and robust used a metal case, which was earthed, would you refuse to plug it in unless wearing rubber gloves?
Put it another way ... when you encounter metal accessories, do you refuse to operate them unless wearing rubber gloves?
This device is not to test for the presence of a risk which would not be a risk to anybody if they didn't use it to test for it. It is to alert people to the presence of a risk to which they are exposed, whether they know it or not, every time they clap hands on an exposed-conductive part.
If there is a fault, then using this tester does not make life an iota more dangerous. But it might lead to it being a great deal safer. Ignorance is not always bliss.
I've asked the question twice, and it is really important.
Touching the button on that tester is exactly the same as holding the earthed metal case of it would be if it were made like that.
So if it were made like that, then would you be happy to plug it in? For the avoidance of any doubt, that is neither a rhetorical not a Socratic question.
Touching the button on that tester is exactly the same as holding the earthed metal case of it would be if it were made like that.
So if it were made like that, then would you be happy to plug it in? For the avoidance of any doubt, that is neither a rhetorical not a Socratic question.
Hi,
Thank you for all the thoughts, very helpful in trying to get my head around it.
One thing I perhaps should have added, was that the Schneider warning symbol shows even when the circuit is off, and when the socket switch is off.
An update:
To try to identify possible village leaking appliances, I unplugged everything I can get to on the circuit and turned the rest off (light and extractor fan, on a fused spur from what I can tell so far), the same results show on both socket testers.
Using a two pole voltage tester on two of the 'warning symbol showing' sockets, and testing them a few times to be sure : L-N 235ish V, L-E 235ish V, N-E 0V
Does this mean that the cause of the warning symbol is me, rather than the CPC ( I'm at a higher potential than the CPC, probably by >/=35V, although it could be less due to an undefined threshold)?
Most importantly, I think, does it mean that the CPC appears to be doing it's job?
Thanks,
Thank you for all the thoughts, very helpful in trying to get my head around it.
One thing I perhaps should have added, was that the Schneider warning symbol shows even when the circuit is off, and when the socket switch is off.
An update:
To try to identify possible village leaking appliances, I unplugged everything I can get to on the circuit and turned the rest off (light and extractor fan, on a fused spur from what I can tell so far), the same results show on both socket testers.
Using a two pole voltage tester on two of the 'warning symbol showing' sockets, and testing them a few times to be sure : L-N 235ish V, L-E 235ish V, N-E 0V
Does this mean that the cause of the warning symbol is me, rather than the CPC ( I'm at a higher potential than the CPC, probably by >/=35V, although it could be less due to an undefined threshold)?
Most importantly, I think, does it mean that the CPC appears to be doing it's job?
Thanks,
Or Occam's razor. The Scneider is faulty.
That would be expected, since it is only 'testing' the CPC which is not switched.
However, everything you have told us continues to make me think that you are simply being misled by an iffy function of a tester.
Kind Regards, John
I doubt that it is 'faulty', rather merely an unreliable tool.
In fact, can't really see how it could be 'faulty', since it almost certainly is nothing more than a passive indicator of the presence of a certain pd between the body of a person and the point being tested (in this case a CPC), just as with a neon screwdriver. If that is what it is, then just as with a neon screwdriver, it can only give 'a warning' if there IS a pd between the person and the test point - but what that pd means is an entirely different question.
Kind Regards, John
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The threshold can be <35 in the same way that a 30ma RCD has a tripping threshold less than 30ma and more than 15ma. There's always a tolerance on the things, and presumably this thing only has an upper bound.
Edit didn't spot the second page, agreed with the consensus and that the tool is not really that reliable but it is a useful indication of a possible issue with the equipotential zone
Edit didn't spot the second page, agreed with the consensus and that the tool is not really that reliable but it is a useful indication of a possible issue with the equipotential zone
No, the threshold is that it must trip at 30mA. That it may trip at less than that does not alter that threshold.
The requirement is that it must trip at 30mA. That a particular device may have a trip threshold of less than that does not alter that requirement.