4 ms·

I'm a little confused why he replaced direct burial CAT6 with fiber because of fear regarding lightning strikes versus the easier and more cost effective soluti

by tssva 5y ago

I'm a little confused why he replaced direct burial CAT6 with fiber because of fear regarding lightning strikes versus the easier and more cost effective solution of installing Ethernet surge protectors at each end.

deleted 5y ago
[deleted]
lazide 5y ago
Surge protectors offer quite limited protection - most will not fully protect against a nearby strike. That said, surely it would also whack everything through the mains connections or gen feed if that was the case? shrug
h2odragon 5y ago
"surge protectors" arent that reliable, and are sacrificial parts. Any length of wire between two electrical ground points might, if there's a lightning strike in the vicinity, be subjected to huge "ground surge" currents. I buried 25 pair copper in a conduit and saw it vaporized; both ends of the conduit run belched flame and smoke and molten bits from a lightning strike that wasn't that close (half mile or less), and certainly not direct.
- ComputerGuru 5y ago
  If you have buried conduit carrying fiber plus Ethernet for redundancy, is disconnecting the Ethernet (when not needed) only at one end sufficient?
  - h2odragon 5y ago
    I'm sure it would have to help; but i would not make any bets in the close presence of lightning and long wires. weird shit happens. My experience says that a free length of wire grounded at a midpoint (like when you disconnect the far end) will still be a potential resonator for enough volts to cross a respectable gap; so unplug it and insulate the unplugged end. Been there, seen the sparks. I maintained various configurations of wire and fiber across a 1/4 mile run through heavy woods on a ridge that gets direct lightning strikes a dozen times a year. nothing involving a conductor that length is simple in that circumstance: see the things the power companies have to do.
    - ComputerGuru 5y ago
      Thanks. I do have the other end up bundled up, but I guess I might as well make a note to disconnect and bundle up the remaining side, too. > I maintained various configurations of wire and fiber Separately or at the same time? What was the wire for in your case if you had it parallel to the fiber, and what did you do to protect it against the lightning strikes? We have it between two directly adjacent buildings that are maybe only 150ft apart (mostly underneath an asphalt access road) but there are no lighting strike rods/redirector on either structure.
      - h2odragon 5y ago
        I had this link between two buildings (no line of sight and radio was too expensive and slow then anyway), it began as redneck engineered "leased line" with modems on either end, with multi pair copper and replacing the modems periodically. The battery that floated that line was kept outside because it would occasionally "vent vigorously" with storms. USR modems had good isolation hardware those so they were pretty robust. Upgraded that to coax Ethernet as soon as I could, 3c509 cards in cheap linux routers at either end of the link, with "modem failover" until the incident that blew away the 25pair. Those cards would lose one or both with every other storm it seemed; but were ~$2/ea off ebay at that point so not so bad. I've got at least one of those motherboards still, somewhere, with multiple bodge wires where i repaired traces blown off by lightning strikes. When we got the fiber we buried the first run, with coax beside it, in conduit again. That lasted a few years before a "landscaping accident" tore out enough that there was no fix. Then we went to suspended coax, and then another fiber tied to that, for a few years, before the business folded. I tried various grounding strategies over the years. The power companies and "best practice" suggest regular connections throughout the span of the line, and at both ends. I found that seemed to invite strikes by being a very good RF ground in the air. Grounding at both ends is bad because of ground surge, pick one or the other end and have the best ground point there you can get, but let the other float, and hope. Also, any actual power system imbalances between two ends of a grounded line will seek to use that nice conductor rather than the cold earth. 150ft isn't that far. Also you haven't got trees to complicate things, they draw lighting and ground it deep. Hickory trees were my bane; they got deep roots that found our high iron sandstone layer and combed the sky for electrons. I'd say consider the switches at either end of that link to be sacrificial buffer parts, and not really worry about it. If its worth considering running fiber under a street, it might be worth considering a free space laser link or something.
dragontamer 5y ago
Surge protectors are for standard load dumps, like air conditioners or other engines that can dump 1000V into your powerlines. Lightning is like 300,000,000 volts. No surge protector is strong enough for that.
- ComputerGuru 5y ago
  You’re not going to see the 300MV unless you had the lightning strike a pole with your cables connected to it, though. I wonder if optically isolated Ethernet couplers (do they even exist??) could work instead of the much more expensive fiber hardware on either end.
  - AdrianB1 5y ago
    Completely optically isolated Ethernet couplers requires a power source on each side, but it can be done; the most accessible one is a set of media converters with a very short optical patch cable. In this particular case to protect both the garage and generator side keeping the CAT6 cable underground you need one optical double conversion on each side and an independent, sacrificial power supply for the copper part converters. Doable, but too complicated.
    - ComputerGuru 5y ago
      Right, that's the obvious option. I was thinking of a barebones "on the wire" approach but I'm not sure that's possible. The fastest integrated optoisolators I can find seem to all max out at 50MBd/s which simply isn't going to be enough to switch 100BASE-TX (which has a ~125MBd/s rate) without needing some sort of ethernet-aware logic (e.g. a primitive MAC controller) on either end to handle buffer overruns. 10BASE-T should be plenty possible though: it only needs a 16MHz channel and even sampling that 2x at the Nyquist rate of 32MHz is still within the capabilities of the $1 optoisolators. 10Mbps is plenty for an application like this one (and probably most industrial control purposes) but it's not exactly something anyone will publicly confess to wanting or using even if it's in order to pay two orders of magnitude less.

by tssva 5y ago

deleted 5y ago

[deleted]

lazide 5y ago

Surge protectors offer quite limited protection - most will not fully protect against a nearby strike. That said, surely it would also whack everything through the mains connections or gen feed if that was the case? shrug

h2odragon 5y ago

"surge protectors" arent that reliable, and are sacrificial parts. Any length of wire between two electrical ground points might, if there's a lightning strike in the vicinity, be subjected to huge "ground surge" currents. I buried 25 pair copper in a conduit and saw it vaporized; both ends of the conduit run belched flame and smoke and molten bits from a lightning strike that wasn't that close (half mile or less), and certainly not direct.

ComputerGuru 5y ago
If you have buried conduit carrying fiber plus Ethernet for redundancy, is disconnecting the Ethernet (when not needed) only at one end sufficient?
- h2odragon 5y ago
  I'm sure it would have to help; but i would not make any bets in the close presence of lightning and long wires. weird shit happens. My experience says that a free length of wire grounded at a midpoint (like when you disconnect the far end) will still be a potential resonator for enough volts to cross a respectable gap; so unplug it and insulate the unplugged end. Been there, seen the sparks. I maintained various configurations of wire and fiber across a 1/4 mile run through heavy woods on a ridge that gets direct lightning strikes a dozen times a year. nothing involving a conductor that length is simple in that circumstance: see the things the power companies have to do.
  - ComputerGuru 5y ago
    Thanks. I do have the other end up bundled up, but I guess I might as well make a note to disconnect and bundle up the remaining side, too. > I maintained various configurations of wire and fiber Separately or at the same time? What was the wire for in your case if you had it parallel to the fiber, and what did you do to protect it against the lightning strikes? We have it between two directly adjacent buildings that are maybe only 150ft apart (mostly underneath an asphalt access road) but there are no lighting strike rods/redirector on either structure.
    - h2odragon 5y ago
      I had this link between two buildings (no line of sight and radio was too expensive and slow then anyway), it began as redneck engineered "leased line" with modems on either end, with multi pair copper and replacing the modems periodically. The battery that floated that line was kept outside because it would occasionally "vent vigorously" with storms. USR modems had good isolation hardware those so they were pretty robust. Upgraded that to coax Ethernet as soon as I could, 3c509 cards in cheap linux routers at either end of the link, with "modem failover" until the incident that blew away the 25pair. Those cards would lose one or both with every other storm it seemed; but were ~$2/ea off ebay at that point so not so bad. I've got at least one of those motherboards still, somewhere, with multiple bodge wires where i repaired traces blown off by lightning strikes. When we got the fiber we buried the first run, with coax beside it, in conduit again. That lasted a few years before a "landscaping accident" tore out enough that there was no fix. Then we went to suspended coax, and then another fiber tied to that, for a few years, before the business folded. I tried various grounding strategies over the years. The power companies and "best practice" suggest regular connections throughout the span of the line, and at both ends. I found that seemed to invite strikes by being a very good RF ground in the air. Grounding at both ends is bad because of ground surge, pick one or the other end and have the best ground point there you can get, but let the other float, and hope. Also, any actual power system imbalances between two ends of a grounded line will seek to use that nice conductor rather than the cold earth. 150ft isn't that far. Also you haven't got trees to complicate things, they draw lighting and ground it deep. Hickory trees were my bane; they got deep roots that found our high iron sandstone layer and combed the sky for electrons. I'd say consider the switches at either end of that link to be sacrificial buffer parts, and not really worry about it. If its worth considering running fiber under a street, it might be worth considering a free space laser link or something.

dragontamer 5y ago

Surge protectors are for standard load dumps, like air conditioners or other engines that can dump 1000V into your powerlines. Lightning is like 300,000,000 volts. No surge protector is strong enough for that.

ComputerGuru 5y ago
You’re not going to see the 300MV unless you had the lightning strike a pole with your cables connected to it, though. I wonder if optically isolated Ethernet couplers (do they even exist??) could work instead of the much more expensive fiber hardware on either end.
- AdrianB1 5y ago
  Completely optically isolated Ethernet couplers requires a power source on each side, but it can be done; the most accessible one is a set of media converters with a very short optical patch cable. In this particular case to protect both the garage and generator side keeping the CAT6 cable underground you need one optical double conversion on each side and an independent, sacrificial power supply for the copper part converters. Doable, but too complicated.
  - ComputerGuru 5y ago
    Right, that's the obvious option. I was thinking of a barebones "on the wire" approach but I'm not sure that's possible. The fastest integrated optoisolators I can find seem to all max out at 50MBd/s which simply isn't going to be enough to switch 100BASE-TX (which has a ~125MBd/s rate) without needing some sort of ethernet-aware logic (e.g. a primitive MAC controller) on either end to handle buffer overruns. 10BASE-T should be plenty possible though: it only needs a 16MHz channel and even sampling that 2x at the Nyquist rate of 32MHz is still within the capabilities of the $1 optoisolators. 10Mbps is plenty for an application like this one (and probably most industrial control purposes) but it's not exactly something anyone will publicly confess to wanting or using even if it's in order to pay two orders of magnitude less.