[AusNOG] Lightning and FTTC - is it really this bad?
Matt Perkins
matt at spectrum.com.au
Mon Jan 25 11:00:01 EST 2021
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
>>
>>
>>
>> --
>> /* Matt Perkins
>> Direct 1300 137 379 Spectrum Networks Ptd. Ltd.
>> Office 1300 133 299 matt at spectrum.com.au
>> Fax 1300 133 255 Level 6, 350 George Street Sydney 2000
>> SIP 1300137379 at sip.spectrum.com.au
>> Google Talk MattAPerkins at gmail.com
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>>
>>> On 25 Jan 2021, at 10:24 am, Thomas Jones <me at 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-bounces at lists.ausnog.net> On Behalf Of Matt Perkins
>>> Sent: Monday, 25 January 2021 9:17 AM
>>> To: Jrandombob <jrandombob at darkglade.com>
>>> Cc: AusNOG at 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 matt at spectrum.com.au
>>> Fax 1300 133 255 Level 6, 350 George Street Sydney 2000
>>> SIP 1300137379 at sip.spectrum.com.au
>>> Google Talk MattAPerkins at gmail.com
>>> PGP/GNUPG Public Key can be found at http://pgp.mit.edu
>>> */
>>>
>>>> On 24 Jan 2021, at 7:00 pm, Jrandombob <jrandombob at 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 <ausnog at 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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--
/* Matt Perkins
Direct 02 8916 8101 Spectrum Networks Ptd. Ltd.
Office 1300 133 299 matt at spectrum.com.au
ABN 66 090 112 913 Level 6, 350 George Street Sydney 2000
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