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Topic Title: Spread spectrum time-domain reflectometry
Topic Summary: Implications for UK fixed wiring installations
Created On: 28 January 2013 02:48 PM
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 28 January 2013 02:48 PM
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rogersmith7671

Posts: 882
Joined: 04 November 2004

Normally this sort of stuff is used for telecom networks or aircraft wiring inspection and the expensive nature of the test kit might rule out its use for anything else but very complex installations.
However, US manufacturers are offering very good hand instruments at the moment which may bring the cost-benefit ratio towards parity soon and therefore, bring about a time when the old "IR"test might become redundant. I am thinking about the advantage that "SSTDR" tests, can provide useful information such as; insulation resistance measurement while the conductor is live, and what possible regulatory (BS:7671) changes might be made to accommodate such technology, especially when there might even be "an app for that" in the not too distant future.

Regards.
 28 January 2013 03:08 PM
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rocknroll

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This is one of the many systems being looked at in preparation for the influx of pre-wired, pre-plumbed, pre-vented modular zero carbon houses that will start to appear in more numbers around 2016, could be a usb socket or socket like the one on your car at the consumer unit, simples, plug in a laptop and go.

Buy your 2, 3 or 4 bedroomed house by mail order.

I keep telling you, do you want to spend the rest of your life as a sniffy nose maintenance electrician changing a few lights and sockets or do you want to be a Building Services Engineer, the clocks ticking.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 28 January 2013 at 03:15 PM by rocknroll
 28 January 2013 03:29 PM
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rogersmith7671

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For a pre-fab building this sort approach would be just right.
Do you think it could be used effectively for custom builds if say, ring circuits and loop in lighting circuits were no longer permitted by regulation? I ask this because the efficacy of this test system relies on near perfect terminations. It may be that the tester may not be able to distinguish between a poor termination and the cable/insulation disconituity they are trying to find.
Ring circuits where brought in simply to save copper (which was in very short supply).

Regards.
 28 January 2013 03:30 PM
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OMS

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It's in use now Roger - one site I work at uses it in conjunction with thermal imaging on safety critical systems supporting Class 1 installations.

At a more mudane level, I've used it (or recommended use of) for identifying cable fault locations - the wheatstone bridge is dead !! -

I don't think it will become a replacement for simple IR testing - and BS 7671 will eventually (possibly via the Guidance Notes) recognise the methodology and equipment.

Regards

OMS

-------------------------
Failure is always an option
 28 January 2013 03:35 PM
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rocknroll

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The reality is that technology that replaces flawed human intervention such as bad decision making and human error has been in place for some time now and is getting more abundant and cheaper by the minute, this is the future.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 28 January 2013 03:48 PM
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rogersmith7671

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Identifying cable fault locations is the good use for which this sort of testing is being promoted. BT are using it to prevent cable theft, by providing an alarm and location of the disturbance.
I assume that once the "test meter" indicates a discontiuity and gives the distance to it from the "tester", the position of any break would be subject to to the building layout, therefore an "as fitted" installation drawing might be desirable regulatory requirement, for a new build say.
I do realize such things are "required" already, but perhaps, not quite specific enough.
Regards
 28 January 2013 03:50 PM
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OMS

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LoL - Human Eyeball Mk1 connected to an engineering brain isn't quite yet defunct, sailor.

Didn't you ever watch "War Games" in the eighties - Defcon 1 based on the Gold Club wi-fi virtual PIR isn't a good plan

Regards

OMS

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 28 January 2013 04:13 PM
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rogersmith7671

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Quote;
"I don't think it will become a replacement for simple IR testing "
Yes i agree, the test methods are very different,and possibly results could be misinterpreted as a safe circuit. perhaps then, the "IR test" tick-box should remain and an "SSTDR" tick-box should be added (with adequate guidance notes of course)?

Regards
 28 January 2013 04:58 PM
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rocknroll

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Originally posted by: OMS

LoL - Human Eyeball Mk1 connected to an engineering brain isn't quite yet defunct, sailor.

Didn't you ever watch "War Games" in the eighties - Defcon 1 based on the Gold Club wi-fi virtual PIR isn't a good plan

Regards

OMS


Fortunately I have already seen applications relating to this subject in one of your ole stomping grounds across the channel, based on the 'black box' principle, a lead to each outgoing ways, one to earth and one to neutral, its surprising what digital technology can do these days that makes the above more of a reality than a dream.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 28 January 2013 05:26 PM
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OMS

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LoL - well, that's the continentals for you - exitable chaps with a Disque Blue on lip and a striped T don't need much encouragement to "do minimum" trust me

Going back to the fault location and BT using it to identify "tampering" I was recently involved in a project that uses TDR on what are basically electric cattle fences but with many more strands (and a lot of volts)

If someone was foolish enough to touch it then the software identifies the location and reports it - once you know where it is then the "appropriate" response can be made in terms of observation, intervention or denial -

Regards

OMS

-------------------------
Failure is always an option
 28 January 2013 11:57 PM
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alancapon

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The TDR is a good tool, but the limitations of the chosen device need to be known. It is likely that any tees will cause a problem, due to the reflection at the joint position, and the question of which branch had the fault reflection on it. Changes in cable size can also cause problems. Often they help in the LV Distribution Network, but sometimes "throwing in a fuse" and listening for the location of the bang gives an faster and more accurate fault location!

Regards,

Alan.
 29 January 2013 09:20 AM
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Jobbo

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Last year Geoff Stokes was advertising his invention in the papers, where the testing engineer was doomed. Has anyone seen his invention in use? He won an award from the IET for it.

http://www.testmarshal.co.uk/
 29 January 2013 02:34 PM
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AJJewsbury

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Originally posted by: Jobbo

Last year Geoff Stokes was advertising his invention in the papers, where the testing engineer was doomed. Has anyone seen his invention in use? He won an award from the IET for it.



http://www.testmarshal.co.uk/


Very interesting. Am I right in thinking it just addresses occasional testing of the installation though?

I've thought for a while that in future we're likely to have "electronic" CUs - with current sensing coils on L and N on each outgoing way, they'd not only offer conventional circuit protection but continuous monitoring & recording. So if you had to come to attend to an RCD trip you could look back through the log to see what the leakage current, voltage and load was at the time, and generally over the days and weeks before. Energy metering per-circuit and alerts (e.g. e-mail to warn that standing leakage current had increased to a worrying level, but before RCDs start to trip). With arduino/raspberry-pi available for £20-£30 now, it doesn't seem impossible.

- Andy.
 29 January 2013 02:41 PM
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Avatar for OMS.
OMS

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that reminds me of the estory of the computing grad sitting at a stand alone terminal and typing in the question "Is there a God" - after a long while the screen flashed back - insufficient capability - unable to answer.

So he linked up all the computers in the university and tried again - after a while back came the same answer.

Some years later he was dealing with a world wide linked system of computers - and his memory drifted back to the same question - so again he typed "Is there a God" - after a brief pause he heard a chuckle - and the screen flashed back the answer - "There is now"

regards

OMS

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Failure is always an option
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