Be great to see a few high res-shots inside.
Matt
On 25/1/21 10:45 am, James Hodgkinson wrote:
This matches with what I've seen/heard/read - the clicking is the NTD turning
off/on power to the DPU, while it tries to check if it's coming online.
We had a DOA DPU and have had one since after a storm, in ... under three
months.
James
On 2021-01-25 09:30 Matt Perkins wrote:
There’s nothing quick about a disconnecting relay. But I do have the
reports of them clicking so perhaps power is applied and they are
looking for some condition that does not appear so power is removed a d
re-applied. Whatever condition they are looking for can not be sensed
due to the fault perhaps there’s some type of op-amp in that sense
circuit that’s sensitive to potential difference and the problem lies
there. Wherever the problem lies given the massive volumes involved
there appears to be a design fault / fit for purpose issue at play
here.
Matt
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/* Matt Perkins
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Office 1300 133 299 m...@spectrum.com.au
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On 25 Jan 2021, at 10:24 am, Thomas Jones <m...@thomasjones.id.au> wrote:
There is definitely a relay internally, not sure what it's actually there for
though - could be for applying power to the line when attempting to power the
DPU, if a short is detected it can disconnect quickly.
Kind regards,
Thomas Jones
-----Original Message-----
From: AusNOG <ausnog-boun...@lists.ausnog.net> On Behalf Of Matt Perkins
Sent: Monday, 25 January 2021 9:17 AM
To: Jrandombob <jrandom...@darkglade.com>
Cc: AusNOG@lists.ausnog.net
Subject: Re: [AusNOG] Lightning and FTTC - is it really this bad?
They had a few hundred to replace in the eastern suburbs in the first week of
Jan the cable there is almost all underground. If anyone has one and can post a
detailed photo of the PCB we can get to the bottom of it but suspect the HV
protection is non existent.
I have heard mention from customers that there is some sort of clicking sound
on a dead NTD not sure what that would be why there would be a relay in there.
Might be just false info Matt
--
/* Matt Perkins
Direct 1300 137 379 Spectrum Networks Ptd. Ltd.
Office 1300 133 299 m...@spectrum.com.au
Fax 1300 133 255 Level 6, 350 George Street Sydney 2000
SIP 1300137...@sip.spectrum.com.au
Google Talk mattaperk...@gmail.com
PGP/GNUPG Public Key can be found at http://pgp.mit.edu
*/
On 24 Jan 2021, at 7:00 pm, Jrandombob <jrandom...@darkglade.com> wrote:
Mea Culpa.
That makes perfect sense. I was considering it from an RF perspective
wherein the mass of earth would theoretically shield the buried
copper. I'd failed to consider that in the case of a ground strike the
buried copper presents a low-resistance path through the lumped
resistance of earth, so it will be the preferential path for the
current to take.
In which case the best I can offer is that perhaps the apparent higher
NTD mortality rate in high lightning areas with aerial lead-ins is
maybe due to them being more susceptible to higher-frequency
components which are induced RF-wise into the aerial cable?
Though without solid data it's hard to say if there's actually a real
correlation between the aerial lead-ins and failures. Since most
aerial cables end up being underground somewhere along the line it
could well be a remote ground strike that is to blame and it's just
the human propensity for pattern matching telling us there is a
correlation.
On Fri, Jan 22, 2021 at 12:51 PM Ross Wheeler <aus...@rossw.net> wrote:
On Fri, 22 Jan 2021, John Edwards wrote:
Underground copper is probably more vulnerable than aerial to lightning.
Lightning strikes the ground, not the copper, but a voltage gets induced
in the copper due to the nearby electromagnetic charge - something that
doesn't happen in air because it's a fairly good insulator.
My experience has shown a different path to lightning damage.
When lightning strikes the ground, or a grounded object, that current
dissipates through the soil, which has a typical resistance of around 500
ohms per metre. If you have tens of thousands of amps flowing, then ohms
law tells us we have potentially huge potential differences over even
fairly short distances.
The copper cable has a very low resistance (by comparison).
If that cable happens to be radial (or oblique) to the current path from
the point of entry, the potential difference from one end of the cable to
the other will be hundreds to many thousands of volts.
Even the insulation of the cable may not be enough to save it, and any
components connected to it which happen to be physically close to the
ground will certainly break down.
This can happen at distances far further away than magnetic induction
alone would explain. It also explains (to me anyway) why I've seen burried
cables damaged part way along their length (where the greatest potential
difference has been).
Just my take on it.
R.
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