Is reddit right about copper cables between buildings?

[wpiman]

As an electrical engineer myself, they've answered all your questions pretty well, in what I think is pretty understandable language. I'm not sure where the disconnect is.

Much appreciated since I had a few glasses of wine and didn't have my glasses on when I typed it out on my phone.

I think the confusion is that all the "grounding" on the sides of the transformers is done at each house side is done in the equipment itself per the spec. If you tried to run a RS-232 or another comm with a ground pin, then this discussion has some merit and becomes very interesting.

 

[wpiman]

Not strictly correct.
When PoE is used - there are direct connections to the internal circuitry, and therefore often to the body or case, of both the PD (Powered Device) and the PSE (Power Sourcing Equipment) as those who have mounted metal bodied cameras to metal flashing well know.

The last time I looked at this, this is usually done using isolated DC to DC converters which have the transformer embedded right into the substrate.. So they are still magnetically coupled..... just within a single part....

The overall point being the user (and/or installer) doesn't need to worry about grounding. It is all handled in the equipment (assuming it is make properly of course). Still recommend surge protection...

But again, optics still might be the way to go here if you trust the power at the other house....

 

[alastairstevenson]

The last time I looked at this, this is usually done using isolated DC to DC converters which have the transformer embedded right into the substrate.. So they are still magnetically coupled..... just within a single part....

Implementation methods vary - that's one approach - but a simpler and cheaper commonly used approach uses a downconvertor with an inductor, not a transformer, therefore having a direct connection to the internal circuitry.

 

[wpiman]

Implementation methods vary - that's one approach - but a simpler and cheaper commonly used approach uses a downconvertor with an inductor, not a transformer, therefore having a direct connection to the internal circuitry.

On the receive side obviously? Would that then require that the transmitter be isolated?

I feel like my day is about to be wasted rereading the IEEE PoE specs.........

 

[alastairstevenson]

Would that then require that the transmitter be isolated?

You would certainly think so, but I've seen a couple of Hikvision NVRs where the ethernet cables were at a solid -48V to ground.
All the outputs have TVP (transient voltage protection) diodes to ground, I didn't check if one or more had gone short due to an overload.

 

[Sybertiger]

I'd pay $100 to not have to dig and screw around with proper burial.

Amazon.com

 

[TonyR]

I'd pay $100 to not have to dig and screw around with proper burial.

Amazon.com

View attachment 180385

Not to mention not having to deal with the issue of metallic cable between buildings, use shielded or not, grounding methods, etc.....the whole kit and kaboodle.

In and working in half a day or less.

I'm next door to FL, which is called by many the U.S.'s lighting capital and I've personally repaired/replaced in 10 years a half dozen such building-to-building CAT-5e cable installs after nearby lightning strikes sent many of the connected devices to the electronics afterlife. The 6 Ubiquiti Layer 2 Transparent Bridges have been purring along nicely since.

Ah, yes as long as there's reasonable LOS, it's my go-to method.

 

[wpiman]

Low voltage only needs to go down 6 inches. I have a conduit out to our generator-- and then I used a trencher to go another 100 feet to an outdoor wifi access point... Through the woods so it isn't like equipment runs over it.

I'd love to see the SNR with those things being 10 feet apart...

 

[TonyR]

I'd love to see the SNR with those things being 10 feet apart...

FWIW, the transmit power on Ubiquiti (and most other mfgs.) can be dialed way down as needed.

 

[pete_c]

Helped a buddy here who built a new home on his farm 10 years ago. He was cheap and went to using cat6 between homes which is working fine today.
That said I originally suggested a wireless bridge to his apartment building in town 13 miles away. This is related to internet. His home is about a mile from the main road near his new home. We prewired his new home before the walls went up all wires went to com closet in the basement.

He is non technical and non dependent on the internet and surfs via his mobile phone.

 

[tigerwillow1]

Not strictly correct.
When PoE is used - there are direct connections to the internal circuitry, and therefore often to the body or case, of both the PD (Powered Device) and the PSE (Power Sourcing Equipment) as those who have mounted metal bodied cameras to metal flashing well know.

Unless the following document is bogus, IEEE 802.3af requires port isolation from the body or case. There are 2 types of isolation, one where all the ports are isolated as a group, the other where every port is isolated individually. See "Electrical Isolation" near the end of the document.
Navigating the IEEE 802.3af Standard for PoE

 

[tigerwillow1]

Low voltage only needs to go down 6 inches.

Since our cameras use nominal 48 vole POE, I'll point out that the 6-inch rule is only for landscape and irrigation control wiring not more that 30 volts. Otherwise it's 6 inches with heavy metal conduit, 18 inches with PVC conduit, or 24 inches for direct burial. This is from NEC table 300.5(A). Is there an exception somewhere for network cables that I can't find? That would be nice.

 

[wpiman]

Since our cameras use nominal 48 vole POE, I'll point out that the 6-inch rule is only for landscape and irrigation control wiring not more that 30 volts. Otherwise it's 6 inches with heavy metal conduit, 18 inches with PVC conduit, or 24 inches for direct burial. This is from NEC table 300.5(A). Is there an exception somewhere for network cables that I can't find? That would be nice.

True, but my assumption was he was trying to go building to building here where each had their own power/ground. POE doesn't necessarily apply in this case...

My access point is currently uses 24VDC injector.

24V DC PoE Adapter - Ubiquiti Store

Ubiquiti 24 V DC PoE Adapters providing a variety of features to help protect your PoE devices.

store.ui.com

With the amount of pine needles that fall in my woods, I expect my 12" cable burial will be 2 feet by the time someone else moves in or I decide to use the 60V injector... I think my extension cord that runs through the woods for the past year on the ground (covered by pine needles now) is a much larger concern.

 

[Sybertiger]

Spectrum buries their network cables from the outside of the house to the pedestal by splitting the ground with a shovel then pushing the wire down. Usually it's 3 to 6 inches and this is common practice here in Florida where we have high sand content. Mine runs about 120 feet but you can see how they bury the cable when they don't feel like messing with tree roots. It's been that way for about 2 years.



And not that low voltage lighting wire is a communication protocol but it's 12-15VAC and typically is just thrown on the ground and maybe mulch or leaves covers it slightly over the years. That's how mine has been for 30+ years.

 

[tigerwillow1]

Spectrum buries their network cables from the outside of the house to the pedestal by splitting the ground with a shovel then pushing the wire down. Usually it's 3 to 6 inches and this is common practice here in Florida where we have high sand content.

I can't offhand quote chapter and verse, but there's an exception to the burial and some other NEC rules that says (in my words) "utilities can do whatever they want to".

 

[TonyR]

I can't offhand quote chapter and verse, but there's an exception to the burial and some other NEC rules that says (in my words) "utilities can do whatever they want to".

To some degree, yes. But like most things, there are exceptions, depending who you are. In this case, it's the railroad...they're older than dirt and pretty much do what they want to and when they want to do it.

I recall, I think it was late 79's or early 80's, the NEC threatened to withhold Federal funding from CA's DOT, CalTrans, if they continued in their plans & specs to allow use of a conductor with green insulation for anything but earth ground. At the time we had red, yellow and green wires for...you guessed it...for the 120VAC red, yellow and green traffic signal indications, white was neutral and earth ground was bare copper. It is a controlled-access situation, only permitted and certified individuals allowed in the traffic signal pull boxes and cabinets, but the NEC prevailed, the hot for the green traffic signal was changed to brown insulation....for everyone BUT.....the railroad! They could color anything anyway they desired but not so the State of California.

 

[Starglow]

Spectrum buries their network cables from the outside of the house to the pedestal by splitting the ground with a shovel then pushing the wire down. Usually it's 3 to 6 inches and this is common practice here in Florida where we have high sand content. Mine runs about 120 feet but you can see how they bury the cable when they don't feel like messing with tree roots. It's been that way for about 2 years.

View attachment 180408

And not that low voltage lighting wire is a communication protocol but it's 12-15VAC and typically is just thrown on the ground and maybe mulch or leaves covers it slightly over the years. That's how mine has been for 30+ years.

Here in NC Spectrum uses a special machine to bury the cable so tree roots aren't a problem. I have seen AT&T hand bury fiber cable the way you described.

 

[rumplestiltskin]

True story: I worked in Juarez 30+ years ago. We had two buildings across the street from one another and wanted to connect them via LocalTalk using those little boxes that plugged into the AppleTalk port of a Mac (and printers). The boxes were daisy-chained with flat phone wire cables and RJ11 connectors. In order to get the two buildings connected, our maintenance crew dug up the street, placed PVC pipes across, and pushed phone wire through. No problem, right?

Well, I was called back to the facility one evening when a cat apparently bridged the terminals of a transformer outside the building and vanished in a puff of smoke. The power cable from the city's electric pole dropped to the ground and sent a strong jolt through the ground which then reached to either end of the phone line under the street. The ends of that cable were connected to a Mac on one side and a laser printer on the other side. Both LocalTalk boxes smoked--literally; I found exploded transistors(?) inside and these two boxes were non-functional. As well, the AppleTalk ports on the two devices were fried. As the Mac had two such ports, I just swapped in a new LocalTalk box and connected it to the other port. One the other side, the printer's AppleTalk board was fried but the company (TI) sent me a new one gratis. No damage occurred to any other devices on the daisy-chain.

I'll note the phone wire that bridged the street (underground) survived the surge and, once the new LocalTalk board/boxes were put into place, we was a stain on ere back up and running. Yes; the maintenance crew had neglected to include any safety grounding/isolation/whatever to the original setup but added it after the incident.

BTW: I still remember the "shadow" of the cat that remained on the wall of the building adjacent to the transformer.

 

[rolibr24]

Spectrum buries their network cables from the outside of the house to the pedestal by splitting the ground with a shovel then pushing the wire down. Usually it's 3 to 6 inches and this is common practice here in Florida where we have high sand content. Mine runs about 120 feet but you can see how they bury the cable when they don't feel like messing with tree roots. It's been that way for about 2 years.

View attachment 180408

And not that low voltage lighting wire is a communication protocol but it's 12-15VAC and typically is just thrown on the ground and maybe mulch or leaves covers it slightly over the years. That's how mine has been for 30+ years.

Before we moved into our house Spectrum was the provider for tv, internet etc. They had their ground tied to the natural gas line coming into the house about a food under grade.........

 

[newfoundlandplucky]

Just finished connecting my detached garage to the house using 10G Ethernet over multi-mode OM3 fiber. The cost difference between copper and fiber was not a big deal. Fiber has less cost these days although SFP+ equipment may be slightly more because it usually supports 2.5G ports in addition to 10G and 1G and PoE.

I peeked at direct burial Ethernet cable too. It has extra water penetration protection using a long lasting gel of some kind. Messy of you have to add RJ45 connector. AFAIK the copper transceivers have magnetics to measure differential signals and are also optically isolated from the rest of the electronics. This is all packaged in a nice little integrated circuit possibly within the RJ45 connector of your equipment's circuit board. Shielding protects all this from external electrical phenomena. These cables break down over time and if they become energized externally you lose. Depends how they degrade.

Lots of effort was spent on trenching, PVC conduit, drainage, and lumber to protect against a shovel strike down the road when I forget where I buried all this stuff. Trenching was the big effort. My only fear is that 40G and 100G in the home is around the corner and none of this really matters because it will have to be done again in a few years.