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I use Powerline Ethernet in my house. I know it essentially broadcasts Ethernet to any outlet in my house via a 2 MHz to 86 MHz signal (source).

My question is, what stops Powerline Ethernet's signal from propagating to the grid, and then to my neighbors' outlets?

I think the grid also uses 60-Hz (source), so it seems like the signals can (in theory) go to my entire neighborhood. What stops this from taking place?

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  • \$\begingroup\$ "What stops this from taking place?" Depending slightly on what the infrastructure of your neighborhood looks like, it's not stopped. Who told you it would be stopped? \$\endgroup\$
    – Mast
    Commented Dec 20, 2023 at 18:54
  • \$\begingroup\$ A filter could stop it, if you're worried about your data leaking to the grid. If I'm not mistaken, something as simple as a properly sized capacitor from phase to neutral in your distribution board. Note there may be safety-related issues, and this is not professional advice. \$\endgroup\$
    – swineone
    Commented Dec 21, 2023 at 13:45
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    \$\begingroup\$ A corollary question - how far could powerline ethernet reach? \$\endgroup\$
    – Criggie
    Commented Dec 22, 2023 at 2:20
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    \$\begingroup\$ @PeterMortensen PoE and Powerline Ethernet are two different things. OP is asking about the latter. I rolled back your edit. \$\endgroup\$
    – winny
    Commented Dec 23, 2023 at 16:08

7 Answers 7

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Nothing stops the signal. Unless you are completely off-grid and as long as the signal is strong enough, you can connect powerline adapters across flat/house boundaries.

I have accidentally "hacked" into my neighbour's unencrypted powerline network and succeeded in using his internet connection. I had to ask him to encrypt his network because my adapters kept connecting to his network.

I was unable to easily establish my own separate network because each time my pairing attempt ended up with my adapters paired to his network.

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    \$\begingroup\$ You should be able to set up your own network if you use a line filter in front of a power strip, then connect both adapters involved in the power strip, set up the network there, and then move them to the final location. Sure it's better if the neighbor has their network secured, but in case of unwilling neighbors this might help. \$\endgroup\$
    – Arsenal
    Commented Dec 20, 2023 at 11:46
  • \$\begingroup\$ Or I could connect the power strip to a battery (with an AC output). I never thought of a line filter, I used the "talk to my neighbor" solution (had to ring a lot of door bells). This happened few years in the past though. \$\endgroup\$
    – andowero
    Commented Dec 21, 2023 at 21:07
  • \$\begingroup\$ AFAIK, most HomePlug adapters come with software to manually set the network key from the Ethernet side. (The ones with Qualcomm/Atheros chipsets are all compatible and have an open-source version on GitHub as 'open-plc-utils'.) \$\endgroup\$
    – user1686
    Commented Dec 22, 2023 at 16:27
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As explained by others the signal has a hard time going through quite a few things, most notably transformers.

But even if the signal goes beyond where you want it to go, powerline communications adapters include encryption, and only adapters that have been paired together can communicate (and decrypt data encrypted by another of the adapters).

If you buy a set they will usually be paired together during manufacturing. If you add an adapter you will need to go through the pairing process before it will work, which requires physical access to the device (usually pressing a button).

So while there could be a signal outside your home, no one can transform that signal into actual data (and vice versa).

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    \$\begingroup\$ The adapters I know are not specifically paired but share a network key ("HomePlugAV") with all other adapters in the world. \$\endgroup\$
    – AndreKR
    Commented Dec 20, 2023 at 5:11
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    \$\begingroup\$ @AndreKR That's just so idiotic. So you can basically only use them when you're somewhere off-grid. Who makes those? All HPAV adapters I ever used had a pairing button and wouldn't connect without it. \$\endgroup\$
    – TooTea
    Commented Dec 20, 2023 at 7:57
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    \$\begingroup\$ the ones I have have pairing buttons and they do sometimes need to get re-paired. \$\endgroup\$ Commented Dec 20, 2023 at 9:05
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    \$\begingroup\$ It seems my comment was misleading. I meant: they all can be paired using the control software or the pairing button, but when you buy them they all come with the default network key, even if you buy them as a set. If you want a private pair, you have to pair them yourself. \$\endgroup\$
    – AndreKR
    Commented Dec 21, 2023 at 4:36
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It basically relies on the power wires not really being very good at carrying the frequencies involved. The signal might be able to propagate to your neighbors in an apartment building, but they'd have to have the correct adapter and possibly overcome some security to access it and that's not very likely. Things like wiring inductance, capacitance, GFI and surge protectors can degrade the signal quite a bit and it's probably not going to get through a pole transformer at all.

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I am using Ethernet over power line at home. If two adapters are on different phases, the signal hardly passes between, and the communication speed is slow.

If one of adapters is connected to power via an extension cord with some kind of overvoltage protection, the signal does not pass. The signal does not pass transformers.

If you live in a private house, the power comes from separate windings, and your neighbors are fed from another winding. If it is apartments (UK as flats), it is possible the neighbors may connect to your network. Adapters have an option to encode transmission; read the manual.

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As others already said power line signals easily can leave your home and spread to the neighbourhood.

This effect can no be avoided completely but can be minimized physically with what can be called "powerline reject filters".

These are filter modules intended to de-couple powerline networks inside of a building (or between buildings, flats, floors etc.).

They strongly suppress the frequency range used by powerline devices - in other words they strongly decrease the spread distance of powerline signals.

An example is the "ALLNET Powerline reject-filter 2,0 - 40Mhz 16A" (use Google to find it), very likely there are other such parts from other manufacturers around.

Of course it is strongly recommended to enable encryption on your powerline network. Thats makes it even harder for "intruders". Encryption does not prevent powerline from spreading out, but it limits the access to it.

Using such a filter does also prevent foreign powerline networks to enter your home. Thus they reduce interference of your own powerline network and may even improve connection quality and bandwidth of your devices.

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Conversely, I know this "feature" was very useful for a friend who did want to network with a neighbour 6 houses down the road.

Here in New Zealand, there are three phases at 120 degrees, connected along the street, but only one is brought into each property, alternating. Thus every third house is on the same 240 V 50 Hz supply, along with every third streetlight. (We don't have 180 degree split-phase 240 V like the US.)

So if one phase drops, it’s possible to see every third house/streetlight is dark, but the other two thirds are normal.

The upshot: the two houses were on the same phase and could have "Ethernet" connection over about 150 metres apart. It was carrying IPX initially for network Doom, and later progressed to carrying IP for accessing media, etc.

Performance was something between 2 and 3 Mbit/sec, so it wasn’t fast, but perfectly adequate.

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I had powerline ethernet adapters in the past in my LAN and found that input power filters on the near apparatus (say printers and PC itself) can "short" the signal and limit speed and distance of communication. Such filters use capacitors between live and neutral wires and they are practical shorts for high frequency signals (that's what they are designed for) while don't drain so much current at mains frequency (50 or 60 Hz, IEC norms limit them at 5 mA max for each device). So I put INDUCTANCES in series of devices power input to avoid such "black hole" for the powerline signal. You can use suitable coils with adequate wire current capability depending by the device power, but I also made some ones just winding PVC insulated wire around a plastic tube (an empty vitamine pills tube, say 1 inch diameter 6 inches long, filled with old rusted iron nails to greatly increase the inductance). It worked! So if you want stop your powerline signals out of your home I could suggest to put large inductances between your home wiring and electricity meter/switchboard (where electricity enters you home), but be sure the coil wire size can bear all your home power! Here in Europe a supply of 3 kW electricity is quite normal and with the voltage of 230V the maximum current reaches 16A, so a 2.5 square mm section (13 AWG) is theoretically sufficient to bear it, but in US I think you need larger wires ...

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  • \$\begingroup\$ This is not a job for a DIY hack and would definitely have insurance consequences in the event of a fire. Your 16 A is per circuit and the filters would have to go upstream of all the socket distribution if the signal is to pass between sockets on different circuit breakers. That means capacity of 40 - 100 A depending on the size of the property. \$\endgroup\$
    – Transistor
    Commented Dec 23, 2023 at 22:30

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