Weird extension lead test results?

[SUNRAY]

I don't get that. How could high resistance conductors get described as a 'short circuit'?

Kind Regards, John

supposition: the test(er) places a s/c on the end of the lead and it reads the loop resistance, there is a maximum resistance set in the tester[ let's give it a random figure, say ½Ω. Plucked out of thin air] a simple pass/fail report if under/over that figure. Therefore report of 'fails short circuit test' as resistance is >½Ω and abreviated to 'Short circuit'.

Just an offering.

 

[mattylad]

OKikoki..
So today I I/R tested L-N using a safeblok so one was used as the earth, this gave a 0.2 MegaOhms reading, this will explain the fault with the 240v lead
and thats considered failed and Im recommending a complete replacement.

The 110v lead doesnt have anything like that but Im just doing the same, or if they can get a length of cable Ill just swap the cable, however given the cost its probably gonna cost less to simply replace them.

I'm also going to have a discussion about how long I should spend trying to figure out a fault, I need to set a limit otherwise it could cost more than it's worth -next time a fail will have a quick check and repair otherwise it will just be failed and a new one sought.

I also found that the 240v extension was good because having 1.5mm wires in the cable, it got used for the portable welder (most likely accounting for the scorch marks in the sockets and the fault in the first place).

I have no way of setting any of the tests apart from making the tester test longer extension leads. As said above - its cheap.
The Metrel is just so simple - that too cannot be changed nor gives anything other than a flashing LED pass/fail. It does however have the 25A earth test.

Cheers.

 

[JohnW2]

supposition: the test(er) places a s/c on the end of the lead and it reads the loop resistance, there is a maximum resistance set in the tester[ let's give it a random figure, say ½Ω. Plucked out of thin air] a simple pass/fail report if under/over that figure. Therefore report of 'fails short circuit test' as resistance is >½Ω and abreviated to 'Short circuit'. Just an offering.

Who knows?! - but, if you are right, then I doubt that one could get much more confusing than describing a test to measure L+N loop resistance as a "short circuit test"!

I think this perhaps illustrates one of the issues about "PATesting". If such testing were undertaken by people who had an adequate understand of what electrical characteristics of the equipment had to be tested (and why) and how to interpret the results, and if they measure those characteristics (all of which will have results in units of volts, amps or ohms, with or without multipliers) using standard measuring equipment, then there presumably would never be a need for discussions like this one.

It seems that an issue may arise when one has some sort of "dumb PATester" kit, which presumably requires little understanding to use, and which results in a discussion (even amongst those with a reasonable degree of understanding) about what/how it is actually testing and why it has declared something as a 'fail'!

Kind Regards, John

 

[SUNRAY]

Who knows?! - but, if you are right, then I doubt that one could get much more confusing than describing a test to measure L+N loop resistance as a "short circuit test"!

As I mentioned before I have a coax cable tester which does call the 3 basic tests: Open, Load & Short because that's exactly what is done on the end of the cable. The measurements & calculated results are a different ball game

I think this perhaps illustrates one of the issues about "PATesting". If such testing were undertaken by people who had an adequate understand of what electrical characteristics of the equipment had to be tested (and why) and how to interpret the results, and if they measure those characteristics (all of which will have results in units of volts, amps or ohms, with or without multipliers) using standard measuring equipment, then there presumably would never be a need for discussions like this one.

Correct.

It seems that an issue may arise when one has some sort of "dumb PATester" kit, which presumably requires little understanding to use, and which results in a discussion (even amongst those with a reasonable degree of understanding) about what/how it is actually testing and why it has declared something as a 'fail'!

Kind Regards, John

The first PAT testing I did entailed building the tester first, this was for BT and a boffin came up with a design, all the tests were a key switch and a pair of pass & fail lamps. completely un calibrated and idiot proof without giving a clue as to what the test really did or an idea of the numerical result.

 

[JohnW2]

As I mentioned before I have a coax cable tester which does call the 3 basic tests: Open, Load & Short because that's exactly what is done on the end of the cable. The measurements & calculated results are a different ball game

Indeed you did, and I don't feel much different about the names of those tests than I do about describing measurement of L+N resistance/impedance as a "short circuit test" !!

Correct. ... The first PAT testing I did entailed building the tester first, this was for BT and a boffin came up with a design, all the tests were a key switch and a pair of pass & fail lamps. completely un calibrated and idiot proof without giving a clue as to what the test really did or an idea of the numerical result.

Exactly. The clue is in "idiot proof", since it would only be an idiot who would be happy to use and trust some machine without understanding what it was doing, how/why it was doing it or what it's 'results' actually meant.

There's an awful lot of this about these days, in any number of fields, facilitated by 'what is now possible' by virtue of all the technological advances (quite unthinkable just a few decades ago) that have occurred - in relation to both 'hardware' and 'software' (both in the most general of senses).

I see this a lot with software - highly sophisticated software (e.g. to do highly complex mathematical things) is now readily available to 'one and all' (and maybe even run it on their mobile phone!), and it's only easy for anyone, including idiots, to feed in data, press a button and get a whole pile of 'output'.

However, far too many people do that without having a clue about what they should be doing, what maths (or logic, or whatever) is going on (and should be going on), whether or not they have 'pressed the right button' and, above all, how to correctly interpret the resulting 'output'.

These technological advantages are invaluable as aids to those who have an adequate understanding (allowing one to do things dramatically more quickly, and to do things which are much more complex than would otherwise be possible) but are incredible potential liabilities in the hands of those who 'know nothing' and simply treat them as 'black boxes' to replace the need for them to understand anything.

Kind Regards, John

 

[mattylad]

Thing is I don't trust the tester I'm using, neither do I trust the megger I have been given (it doesn't give good understandable results).

The PAT tester does an Earth continuity test and gives the resistance with a pass or fail, then it does an IR test and gives the results including a pass or fail, then for extension leads it does a polarity check - it may also be doing a resistance check - possibly along each individual wire (end to end) and comparing them and shorting the ends out (I think I hear a relay click) and doing a full loop (possibly) however when it has finished it either gives it a pass or if it fails it might (just might) give a vague reason why.
Short - indicates a short between the connections - does not say which (although logic suggests its L>N as otherwise it would fail the IR).
Open - indicates the L>N are open circuit

The tester nor its manual actually give much of a clue to whats going on.

The thing that really puzzled me about these leads is that it says there is a short yet I cannot find it using other equipment, it does not say its a direct short, or a high impedance short - just "short" (not very helpful).

That's why I fudged an IR test on the L>N which suggested its 0.2meg so its a high resistance short, possibly a feint whisker, moisture or carbon buildup.
Given that there is damage to the cable half way along its length and that the lead is a few years old so has taken some battering I'm simply failing it and getting it replaced.

And your partially right John, in that I'm not 100% in what I am doing or the results as AC theory was a long time ago for me and I have not had much dealings with it at this level since, so I have forgotten a lot of it, I'm more of a lower voltage electronic person.

Would you be comfortable figuring out the impedance characteristics and keeping multiple set of differential pairs within their correct skew while routing a PCB with them on, going to an IC with over 2000+ connections on? I would! So "idiot" is a rather offensive term to be using in a reply.

 

[bernardgreen]

Measuring insulation resistance with steady state DC ( no ripple voltage ) will give a true result that will not take any account of the capacitance of the cable. If the test applies a DC voltage with some ripple then the capacitance of the cable will allow current to flow and the resistance reading will be lower than the actual resistance of infinity. The higher the frequency of the ripple the lower the false resistance reading will be.

 

[SUNRAY]

And your partially right John, in that I'm not 100% in what I am doing or the results as AC theory was a long time ago for me and I have not had much dealings with it at this level since, so I have forgotten a lot of it, I'm more of a lower voltage electronic person.

Would you be comfortable figuring out the impedance characteristics and keeping multiple set of differential pairs within their correct skew while routing a PCB with them on, going to an IC with over 2000+ connections on? I would! So "idiot" is a rather offensive term to be using in a reply.

I don't see anyone calling you an idiot, neither do I think anyone is an idiot if they are asking for advice on something which is outside their knowledge base.
Quite the opposite, I would call them an idiot for not asking.

We all have out skill sets and I'm happy to admit when I don't know something and rely on others to fill the gap, as indeed I'm happy to fill the gap for others.

 

[JohnW2]

Thing is I don't trust the tester I'm using ...

Indeed - and, as I've said, I'm not sure that any of us do - or, rather, that any of us are are sure what it is doing and what its reported results mean, even if it is 'working as intended' (which it may not be). ... and you seem to be in the same position, given the "may", "possibly" (x2) and "might" (and your last sentence) when you write:

The PAT tester does an Earth continuity test and gives the resistance with a pass or fail, then it does an IR test and gives the results including a pass or fail, then for extension leads it does a polarity check - it may also be doing a resistance check - possibly along each individual wire (end to end) and comparing them and shorting the ends out (I think I hear a relay click) and doing a full loop (possibly) however when it has finished it either gives it a pass or if it fails it might (just might) give a vague reason why.

You go on to write:

Short - indicates a short between the connections - does not say which (although logic suggests its L>N as otherwise it would fail the IR).
Open - indicates the L>N are open circuit

Given the above, how are you sure of that - is that stated in the manual? As SUNRAY has said "Short", or even "Short circuit test" has been known to be used to mean an L+N loop resistance/impedance test undertaken when the L&N were 'shorted together' at the other end!

That's why I fudged an IR test on the L>N which suggested its 0.2meg so its a high resistance short .... The thing that really puzzled me about these leads is that it says there is a short yet I cannot find it using other equipment, it does not say its a direct short, or a high impedance short - just "short" (not very helpful).

That's the crazy thing about what you are seeing/reporting - and the reason why I suggested early on that I 'suspected' your machine. To electricians, there is really no such thing as a "high impedance short" - a "short" is generally taken (often defined) as being 'of negligible impedance' (usually <1Ω, certainly less than a few kΩ). If the "short" test is looking at the L-N resistance/impedance, then it's doing the same as an L-N IR test - so it's impossible that that resistance can be high enough to pass the IR test yeat also low enough to be called "a short"!

And your partially right John, in that I'm not 100% in what I am doing or the results as AC theory was a long time ago for me and I have not had much dealings with it at this level since, so I have forgotten a lot of it, I'm more of a lower voltage electronic person. ... Would you be comfortable figuring out the impedance characteristics and keeping multiple set of differential pairs within their correct skew while routing a PCB with them on, going to an IC with over 2000+ connections on? I would! So "idiot" is a rather offensive term to be using in a reply.

You seem to have misunderstood. I certainly was not suggesting that you are an idiot, and am sorry if you got that impression. Indeed, the fact that you are querying this result, have investigated it logically (using other equipment) and are discussing it knowledgeably and sensibly indicates that you are anything but an idiot!

What I was doing was commenting, in general, on the mention of attempts to produce (what are colloquially described as) "idiot-proof" products ('hardware' or 'software') - designed to be theoretically usable by people who had no understanding of what they do, how they do it, what should be done (and why) and no real understanding of what the 'results' mean.

I'm sure that there are many things that I do professionally (in fields remote from anything electrical) that you wouldn't have a clue how to do, and equally sure that the converse will also be true - but that does not make either of us idiots. What I would not be 'comfortable' with would be for you to be given 'a box', or piece of software, which seemingly enabled you to do what I do without any knowledge or understanding (just 'an answer') and I'm sure you would feel similarly if I were given a box or software which seemingly allowed me to do your PCB design - again, with minimal understanding.

So, 'idiocy' does not really come into it (for either of us!). I would, however, personally say that it is 'unwise' (i.e. I would be uncomfortable to do it myself) to utilise (let alone 'rely on') a bit of hardware or software if I did not have a reasonable understanding of what it was doing, how it was doing it and what the 'results' actually meant.

We all know of the potential pitfalls of 'blindly' relying on 'black boxes' or machine logic. In the early days of computer, an oft-quoted hypothetical example was that of a piece of software designed to advise the user which of two watches they should buy - one that lost a second every day and the other that didn't work at all. Needless to say, the computer chose the latter. Someone who 'actually understood what it was doing' would/should have realised that what it was doing was calculating how often the time it indicated would be 'correct' - and that the "buy the one that doesn't work at all" result arose because that one would indicate the correct time twice every day, whereas the former would only be correct about once every 118 years! An understanding of what technology 'is actually doing' can be useful in such situations!

Kind Regards, John

 

[JohnW2]

I don't see anyone calling you an idiot, neither do I think anyone is an idiot if they are asking for advice on something which is outside their knowledge base. ... Quite the opposite, I would call them an idiot for not asking. ... We all have out skill sets and I'm happy to admit when I don't know something and rely on others to fill the gap, as indeed I'm happy to fill the gap for others.

Indeed. As you will see, I was busy writing exactly the same (very much less succinctly!) when you posted this.

Kind Regards, John

 

[bernardgreen]

We all know of the potential pitfalls of 'blindly' relying on 'black boxes' or machine logic.

I was reminded this morning of this misplaced trust in a "black box" with unknown technology inside it.

It was an intentional fraud but an extreme example of people having blind faith in the words of the salesman who was selling useless equipment.

LINK

 

[JohnW2]

I was reminded this morning of this misplaced trust in a "black box" with unknown technology inside it. It was an intentional fraud but an extreme example of people having blind faith in the words of the salesman who was selling useless equipment. LINK

Interesting, but I would say that 'fake products' are very different from what I was talking about.

I was talking about 'real' products which properly do what they purport to be doing, but which can result in all sorts of problems if/when used by people who do not have an adequate understanding *(of what the 'boxes' are doing, whether that is appropriate for their situation and how to interpret ;'the results' etc. etc.).

Kind Regards, John

 

[bernardgreen]

Where does one draw the line between items that are "absolutely fake" and those that are badly designed / documented leading to confusion of the person using it.

 

[JohnW2]

Where does one draw the line between items that are "absolutely fake" and those that are badly designed / documented leading to confusion of the person using it.

I was perhaps wrong to use the word 'fake', since that includes functional products which are (usually inferior) 'impersonations' of proprietary products.

What I was meaning to refer to are "fraudulent" products, in which no attempt has been made to produce a product which could possibly do what it claims to do - e.g. the "MCBs" which contained nothing but a switch, "laptops" which contain no electronics or, maybe per your link, a bomb detector which contains nothing that could detect bombs.

My earlier comments were about something very different - often excellent, well designed and documented, products, but which are very easily misused by people who do not have the necessary understanding (of everything relevant). There must be an almost astronomical list of products (anything from a screwdriver to an A380) which are excellent in the hands of those who understand how, why and when to use them, but not (sometimes dangerously) in the hands of those who do not.

The specific concern I was voicing related to attempts to produce "idiot-proof" products, deliberately intended to be 'usable' by people with no relevant knowledge understanding. If it were 'perfectly idiot-proof' I suppose that might be OK, but such is probably an impossibility.

You are introducing a third category - that of poorly designed/documented products which, if bad enough, might not be 'fit for purpose', but that's a different matter.

Kind Regards, John

 

[mattylad]

https://www.jprelec.co.uk/pdffiles/uni_t_ut528_pat_tester_user_manual.pdf
Page 16.
Although as per some other things, it does not conform exactly to what the manual says.