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 [email protected]
Fax 1300 133 255 Level 6, 350 George Street Sydney 2000
SIP [email protected]
Google Talk [email protected]
PGP/GNUPG Public Key can be found at http://pgp.mit.edu
*/
> On 25 Jan 2021, at 10:24 am, Thomas Jones <[email protected]> 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 <[email protected]> On Behalf Of Matt Perkins
> Sent: Monday, 25 January 2021 9:17 AM
> To: Jrandombob <[email protected]>
> Cc: [email protected]
> 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 [email protected]
> Fax 1300 133 255 Level 6, 350 George Street Sydney 2000
> SIP [email protected]
> Google Talk [email protected]
> PGP/GNUPG Public Key can be found at http://pgp.mit.edu
> */
>
>> On 24 Jan 2021, at 7:00 pm, Jrandombob <[email protected]> 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 <[email protected]> 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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