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. > _______________________________________________ > AusNOG mailing list > AusNOG@lists.ausnog.net > http://lists.ausnog.net/mailman/listinfo/ausnog _______________________________________________ AusNOG mailing list AusNOG@lists.ausnog.net http://lists.ausnog.net/mailman/listinfo/ausnog _______________________________________________ AusNOG mailing list AusNOG@lists.ausnog.net http://lists.ausnog.net/mailman/listinfo/ausnog