Failed PAT

[JohnW2]

In theory no. In practice? I'll draw a comparison; plug an equivalent coiled cable into a balanced amplifier input and turn the volume up, then unroll it.

If I understand you correctly, that surely has absolutely nothing to do with what we're discussing, since its not a case or two identical AC currents flowing in opposite directions along two intimately related conductors in a cable? Indeed, if (as I think you're suggesting) there is nothing connected to the far end of the cable, there will be virtually no current flowing at all, in either conductor.

Indeed, IF it were a truly (perfectly) balanced amplifier, then you would only hear something if the two conductors in the cable were picking up different things (by inductive and/or capacitive coupling) from the same 'external source(s)' - and it seems hard to believe that would happen given the intimate proximity of the two conductors (whether coiled or not).

Am I missing something?

Kind Regards, John

 

[SUNRAY]

If I understand you correctly, that surely has absolutely nothing to do with what we're discussing, since its not a case or two identical AC currents flowing in opposite directions along two intimately related conductors in a cable? Indeed, if (as I think you're suggesting) there is nothing connected to the far end of the cable, there will be virtually no current flowing at all, in either conductor.

Indeed, IF it were a truly (perfectly) balanced amplifier, then you would only hear something if the two conductors in the cable were picking up different things (by inductive and/or capacitive coupling) from the same 'external source(s)' - and it seems hard to believe that would happen given the intimate proximity of the two conductors (whether coiled or not).

Am I missing something?

Kind Regards, John

The result of the test will be noise, possibly even detecting a radio transmission then when unrolled the noise will be massively reduced. the difference only being the inductance (possible capacitance) and the noise is the PD between the balanced pair. If it happens on that test then it stands to reason there will be noise (however little) on a mains cable too.

 

[ericmark]

The main problem at you say is lack of ventilation and bunching, one only has to look at derating factors in the regs to see what difference it makes.

In the main there are over temperature cut outs to protect the cable, however seen nothing to say without these it should be a fail.

As to a caravan with the 25 meters of 2.5 mm² cable I have not seen a real problem with 16 amp, the problem seems to be when lighter cable is used. I found the cable tidy

would not take 25 meters of 2.5 mm² normally I would lay as figure of 8, however is this cable part of the installation or an appliance? I have seen once or twice where sites have asked for an electrical certificate, but I would say it is only valid until unplugged and moved, so one would need a loop impedance meter and RCD tester with the caravan. I do see how a simple plug in tester is a good idea to ensure there is an earth and line and neutral correct way around

and yes the plug in tester would show this, however to complete paperwork every time you moved site is not really practical. It would need some one who could show they had the skill required.

 

[RandomGrinch]

. I do see how a simple plug in tester is a good idea to ensure there is an earth and line and neutral correct way around

and yes the plug in tester would show this,

And now for a metaphysical question - Is the plug-in tester an appliance that needs PAT'ting?
Plugging test devices like this into a tester will throw up all sorts of errors!

We were often asked facetiously, if our PAT testers had been PAT'ted, and we have to reply 'No'!
However, they were calibrated and inspected anually by the manufacturer

 

[JohnW2]

The result of the test will be noise, possibly even detecting a radio transmission then when unrolled the noise will be massively reduced. the difference only being the inductance (possible capacitance) and the noise is the PD between the balanced pair.

Yes, I understood what you were suggesting would happen but, as I said, that really shouldn't happen with an amplifier which has differential inputs (i.e. a 'balanced amplifier'), since I can think of no reason why there should be any significant difference between what was 'picked up' (by whatever process) by one conductor and what was picked up by the other one - hence little or no PD between the two.

If the amplifier did not have differential inputs then it could be totally different, since one would then really be talking about an 'antenna' connected to the input, and what noise, radio transmission or whatever that then got picked up (and amplified) would vary considerably according to how the cable was physically arranged - and we are, of course, now talking of frequencies much higher than 50Hz

If it happens on that test then it stands to reason there will be noise (however little) on a mains cable too.

Maybe, but not 'different noise' in the two adjacent conductors - so little or no PD between them.

Anyway, as I think you'll agree, this tangent is totally irrelevant in relation to this thread (and quantitatively irrelevant to anything), so I really don't think it's worth pursuing further.

Kind Regards, John

 

[JohnW2]

And now for a metaphysical question - Is the plug-in tester an appliance that needs PAT'ting?

If they are mains-powered and/or designed to sometimes be connected to live 'mains', then I see no reason why they shouldn't 'need PATesting' - but therein, of course, starts an endless "and then ... and then.... and ...." chain of required events

We were often asked facetiously, if our PAT testers had been PAT'ted, and we have to reply 'No'! However, they were calibrated and inspected anually by the manufacturer

Given that there appears to be no legal definition of what PATesting consists of (or even what should be subjected it), would not "the annual calibration and inspection by the manufacturer" qualify as something which would satisfy the owner's obligations?

Kind Regards, John

 

[RandomGrinch]

If they are mains-powered and/or designed to sometimes be connected to live 'mains', then I see no reason why they shouldn't 'need PATesting' - but therein, of course, starts an endless "and then ... and then.... and ...." chain of required events

The only reasonable test to do on an item like this is the visual inspection (Not a big issue, >90% of our failures are found during visual inspections, or the rattle test!).
But we still need to record the results and afix a tiny little green label!

would not "the annual calibration and inspection by the manufacturer" qualify as something which would satisfy the owner's obligations?

Yes, exactly!

 

[Harry Bloomfield]

The inductance does have a little effect and I stress LITTLE. If the cable is wound in a non inductive way it makes a 'just measurable' difference.

If L and N closely follow the same route - the current flow in one, will precisely cancel the flow in the other.

 

[JohnW2]

If L and N closely follow the same route - the current flow in one, will precisely cancel the flow in the other.

Exactly (provided, of course, the two conductors are carrying current to/from the same load) - and, as I've been saying, that remains the case whether the cable is straight, coiled or anything else.

SUNRAY's comments amount 'noise pickup' relates to a totally different situation. In that case there are not 'currents travelling in opposite directions' in the two conductors and, in terms of the actual 'pickup', I see no reason why the two conductors should pick up anything different. Hence, as I've said, since there should be no 'noise PD' between the conductors, a true balanced/differential amplifier should not see any 'signal'.

Kind Regards, John

 

[RandomGrinch]

in terms of the actual 'pickup', I see no reason why the two conductors should pick up anything different.

The earth conductor may do though!

 

[JohnW2]

The earth conductor may do though!

If it's an intimately associated with the other two conductors, I don't see why it should - but, even if it did, that should not be seen by a true differential amplifier.

In any event, the earth conductor has not been part of the equation in relation to what people have been arguing about!

Kind Regards, John

 

[SUNRAY]

As said before it is a number of tens of decades since I'd seen one of these 'screw top' 5A plugs:

Monday I attended a fault reported as 'Everytime I touch the computer I get electrocuted'.
I found an extension lead plugged into the adjacent room:

At least someone had thoughtfully marked the positive and negative pins:

And the wiring side of it:

At least the 'cable grip' had been used but not big enough for 2 lots of insulation.

The annoying thing it the 5A switched socket is on the elderly 3/0.029" lighting circuit but the surface mounted ring circuit is brown/blue T&E in trunking. Adding a couple of DSSO's into the ring was exceptionally easy from the trunking the other side of the wall as the hole was already there, presumably from a previous pipe.

 

[JohnW2]

As said before it is a number of tens of decades since I'd seen one of these 'screw top' 5A plugs:...

I think I still have some 'hoarded' ones somewhere (and certainly plenty of light switches with 'screw off' {'without a tool'} covers)!

Kind Regards, John

 

[plugwash]

The only reasonable test to do on an item like this is the visual inspection

Unfortunately I think you are probablly right, you could measure the earth leakage, but without documentation from the Manufacturer on what is expected (I looked in the manual and couldn't find any numbers) you would have nothing to compare it to. As test equipment you can't reasonably expect it to conform to the levels expected of a normal appliance.

 

[SUNRAY]

I think I still have some 'hoarded' ones somewhere (and certainly plenty of light switches with 'screw off' {'without a tool'} covers)!

Kind Regards, John

Sadly I think I do too and when I can shift enough rubbish to get to those drawers I hope I will be able to dump it all, contents and drawer unit.

EDIT: I'll add to that and say I still have a suitcase full of the cables we used for public address going back to 1960's when we used loads of 5A plugs and sockets for mains and 2A for loudspeakers.