Contact voltage on PE-conductor

[JohnW2]

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.

Indeed. It's just a slightly unusual way of putting it. One wouldn't normally say that an RCD had a trip threshold of <30mA - rather, one would say that it had a maximum threshold of 30mA (and a minimum threshold of 15mA).

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

Despite some of the things that have been said in its defence, I still don't see it as qualitatively different from a neon test screwdriver. Whilst the latter might also to be said to be a "a 'useful' indication of a possible issue with the equipotential zone", I doubt that one would find many people defending it's use for such a purpose!

Kind Regards, John

 

[JohnW2]

No, the threshold is that it must trip at 30mA. That it may trip at less than that does not alter that threshold.

That's not "the threshold" - it's the maximum threshold.

Kind Regards, John

 

[EFLImpudence]

The requirement is that it must trip at 30mA.

So, that is THE threshold.

That a particular device may have a trip threshold of less than that does not alter that requirement.

It does not have a trip threshold less than that; the threshold is still 30mA.

That it trips at less than the threshold does not alter that required threshold.

 

[EFLImpudence]

That's not "the threshold" - it's the maximum threshold.

I disagree. That is the only stated value at which it must trip, so that is the threshold.

 

[JohnW2]

I disagree. That is the only stated value at which it must trip, so that is the threshold.

We may have different ideas about what "threshold" means.

Although Schneider have chosen to use it, it's not a word normally used in specifying requirements of operating characteristics. The normal language is to specify a maximum and/or minimum requirement for the quantity in question.

Kind Regards, John

 

[EFLImpudence]

Yes, perhaps that is the problem.

 

[JohnW2]

Yes, perhaps that is the problem.

Indeed. "Threshold" is usually used to indicate the value of some quantity above/below which 'something changes' (e.g. an income level at which rates of tax or NIC change), rather than a specified 'limit' of some quantity.

Kind Regards, John

 

[EFLImpudence]

Indeed. "Threshold" is usually used to indicate the value of some quantity above/below which 'something changes' (e.g. an income level at which rates of tax or NIC change), rather than a specified 'limit' of some quantity.

Even so - I don't see how one can have a threshold of "less than {a quantity}".

The VAT threshold, for example.

 

[JohnW2]

Even so - I don't see how one can have a threshold of "less than {a quantity}". The VAT threshold, for example.

In terms of the normal use of language, I don't think one normally can.

I suppose that one could have a situation in which one was free to choose a 'threshold of choice', but within certain specified limits.

Similarly, I suppose that one could talk of a 'threshold' between the residual currents at which an RCD would be tripped or non-tripped - which would not be a fixed current (but, rather, anything in the range 15-30mA) - but we don't say things like that.

Kind Regards, John

 

[Bryn2017]

Hi,

So, how will the possible problem be ruled in or out definitively?

Any thoughts on why some sockets on the same circuit show the warning sign, and others don't? It consistently shows the same ones as a problem. One is a spur, the others are on the ring. This has made the situation more confusing to me, as surely they would all respond the same, or if the Schneider was a bit random, it wouldn't show the same sockets as the problem every time?

Thanks,

 

[JohnW2]

So, how will the possible problem be ruled in or out definitively?

You would need to use some 'proper' 2-pole measuring device to measure any voltage between the 'earths' of the sockets concerned and some manifestation of 'true earth' - or, as a second best, between 'earths' of sockets which exhibited this problem with your tester and ones which didn't.

Any thoughts on why some sockets on the same circuit show the warning sign, and others don't? It consistently shows the same ones as a problem.

The tester relies upon the 'coupling' between your body and anything else around (hopefully 'true earth', but it could also be electrical fields created by currents in nearby cables etc.). If, as is probably the case, your body is in different places when testing different sockets, then that could explain differences.

I really very much doubt that there is any problem but if you feel the need for reassurance, you'd probably need to get an electrician, with appropriate test equipment, to check it out.

Kind Regards, John

 

[ban-all-sheds]

So, that is THE threshold.

No - it's the maximum threshold required by the standard.

It does not have a trip threshold less than that; the threshold is still 30mA.

No, a device can have a threshold different to the one required by the standard, as long as it is different in the right direction and the standard only requires a minimum, or maximum, threshold.

That it trips at less than the threshold does not alter that required threshold.

Indeed it does not, but it does "alter" the threshold for operation of that particular device.

In terms of the normal use of language, I don't think one normally can.

I suppose that one could have a situation in which one was free to choose a 'threshold of choice', but within certain specified limits.

Similarly, I suppose that one could talk of a 'threshold' between the residual currents at which an RCD would be tripped or non-tripped - which would not be a fixed current (but, rather, anything in the range 15-30mA) - but we don't say things like that.

Kind Regards, John

IMO all of us, you, me, EFLI, Schneider, are being a bit sloppy, or at least elastic, with our use of "threshold".

Let's remember that a threshold is actually a physical barrier across the bottom of a doorway into a building or room which is there to stop the thresh used as a floor covering from escaping, i.e. to hold it in place in the room.

Regulations or standards can require a device to have a maximum (or minimum) threshold, the crossing of which causes it to do something. IHNI if the requirements for RCDs specify minima, but if they don't then one which tripped after an imbalance of a microamp was sustained for a microsecond would comply with the requirements for the 30mA device we all know and love. Its threshold would be way below the maximum required, but the fact that it was would not change the fact that the standard specified a threshold, nor that the device had a different one. (Although I suspect that such a device would not be well loved.)

I think we do all know what Schneider are trying to say, and it does make sense - the device will flag a problem if a PD between true earth and installation earth exceeds X volts, where X is to some extent indeterminate, but which they say will never exceed 35V.

It's threshold, i.e. the line which it recognises has been crossed is variable, and will vary from minute to minute, I expect, and will be influenced by any number of external factors, but what they are saying is that at any given point in space-time it will have a threshold which is < 35V.

 

[ban-all-sheds]

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.

Well I'm sorry, John, that you feel unable to answer that question, for it really is not a trick one, nor one where any games are being played.

The Schneider device invites the user to touch an earthed exposed-conductive-part, so I was genuinely interested to understand why you regarded that as an undesirable thing to ask people to do unless you regarded the whole idea of there ever being exposed-conductive-parts as equally undesirable.

 

[John D v2.0]

regarded the whole idea of there ever being exposed-conductive-parts as equally undesirable.

Let's not go down that road again

 

[John D v2.0]

It's threshold, i.e. the line which it recognises has been crossed is variable, and will vary from minute to minute, I expect, and will be influenced by any number of external factors, but what they are saying is that at any given point in space-time it will have a threshold which is < 35V

Agreed, indeed I think we can zoom in or out. wI,fe zoom in. slightly, we can see that although each individual device has a threshold that it trips at, which may very depending on temperature, load, etc. There is also an additional threshold which is the threshold for devices being compliant with the spec. If the device's threshold crosses this more abstract compliance threshold then it's no longer compliant.
So to use the original definition, the devices are a room with current on the floor that may cross the threshold. The set of compliant devices are also in a room with a threshold where the non compliant devices are outside the threshold.

Or you can look at it with set theory of you like. The set of all currents for one device that would trip it, and the more abstract set of all devices all their individual tripping points which comply with the spec