Ethernet Surge Protection - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: November 28, 2016, 07:58:12 pm
content: It seems yesterday we copped a bit of a storm. When I got home I found that my cheap Netcomm modem/router completely died and a surge also took out one of my Sonos speakers. Luckily the switch both were connected to was fine.I was looking at Ethernet surge protectors in order to protect the incoming phone line (and also downstream devices if a surge does make it through and destroy the switch). They come in varieties from several hundred dollars to a more modest AUD$38 for the Tycon ESP-1000-POE. Specs and schematic are as follows:Operating Voltage:Data 5v; POE 48vClamping Voltage:70v POE (All 8 Pins)Max. Surge Discharge Current:5KA (8/20 us)Peak Pulse Current:100A (10/1000 us)Protection Mode:Differential & Common ModeInsulation Resistance:>1000 MOhmShunt Capacitance:<25 pFResponse Time:<5nsThere is also a 100Mbps, 24v POE model with the same specs except the clamping voltage is 7.5v on the Data pins and 40v on the POE pins.Not knowing much about this kind of stuff, would this offer reasonable protection for non-direct lightning strikes? We mostly have overhead power and telephone cabling.

author: fubar.gr
author_rank: Unknown
timestamp: November 28, 2016, 08:23:55 pm
content: I guess the surge came through the telephone line, so that's what you should protect first!

author: Halcyon
author_rank: Unknown
timestamp: November 28, 2016, 08:26:33 pm
content: Quote from: fubar.gr on November 28, 2016, 08:23:55 pmProbably. This is why I posted the question. I don't care if the crappy modem blows up, as long as it doesn't take anything else with it.

author: bktemp
author_rank: Super Contributor
timestamp: November 28, 2016, 08:50:53 pm
content: Quote from: Halcyon on November 28, 2016, 08:26:33 pmBut telephone lines are much easier to protect than ethernet cables, because telephone lines operate at a lower frequency and can tolerate a much higher voltage.Adding some large TVS diodes + gas discharge tubes can easily shunt 20kA, much more than your ethernet protector can handle.

author: Monkeh
author_rank: Super Contributor
timestamp: November 28, 2016, 09:04:21 pm
content: Quote from: Halcyon on November 28, 2016, 08:26:33 pmGrab a pair of media converters, use fibre.

author: Halcyon
author_rank: Unknown
timestamp: November 28, 2016, 09:20:12 pm
content: Quote from: Monkeh on November 28, 2016, 09:04:21 pmYep, good idea! My switch has SFP modules anyway, may as well use them.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2016, 09:51:27 pm
content: I wouldn't suggest putting TVSs directly on Ethernet wires, but as mentioned, GDTs are good for big surges (including lightning induced surge). And making sure the outward-facing equipment (the modem), and any protection it might contain, is well grounded, will shunt that energy away from the rest of your system, as well as possible.Not that the rest your system necessarily will be well shielded or grounded, with respect to that ground, either -- which is another thing to try and arrange. Yes, design includes where power and signal cables are routed in the building!...Tim

author: Halcyon
author_rank: Unknown
timestamp: November 29, 2016, 03:06:46 am
content: Thanks for your feedback Tim. Yeah it's going to be hard grounding everything properly as I have Ethernet running all over the place. The best thing I can do I think will be to create an air gap as much as possible between the modem and the rest of the network by using fibre optic as Monkeh suggested. For other items such as my Sonos speakers, I might create a separate VLAN and run them purely off the Wi-Fi network.I've traced the surge back to the phone line, not the power cabling. It entered the house via the modem and blew the arse out of that (the 12v plug pack survived though). It then travelled up the Ethernet cabling and into a Cisco catalyst switch, from there I guess it found the nearest ground and blew the Sonos speaker that was connected to the Ethernet port right next to the router. The switch and both ports survived though.Almost everything else (desktop PC's, servers, media centre) are all protected by AC surge protectors and/or a UPS with some surge protection built-in.If I can at least isolate most of the risk to the new modem and media converter, we're talking <$100 of equipment to replace if it happens again. That I'm happy to wear if it means the rest of the network is safe(er). I'm more annoyed that I have no internet at home until the new modem arrives today or tomorrow.

author: Monkeh
author_rank: Super Contributor
timestamp: November 29, 2016, 03:07:51 am
content: Keeping spare modems on hand is wise with overhead cabling.

author: SeanB
author_rank: Super Contributor
timestamp: November 29, 2016, 04:17:58 am
content: At phone service entry put a GDT arrestor, with a heavy cable going straight down ( short as possible) to a ground rod ( or more if the soil is dry or a poor conductor) right below it. Wind a common mode choke out of extra cable ( a loop of around 20 turns around 20cm diameter) ahead of the GDT unit so the spike will have some attenuation.

author: Halcyon
author_rank: Unknown
timestamp: November 30, 2016, 07:44:16 am
content: Damage count so far:1x Netcomm Modem/Router1x Sonos Play:3 Speaker1x NIC on my desktop machine (lucky I have two)1x Line card/whatever is at the node that makes the internet workIt's more of an inconvenience than anything. This wouldn't have happened if NBN Co. just installed bloody fibre to the premises to begin with!

author: BBBbbb
author_rank: Unknown
timestamp: November 30, 2016, 01:29:53 pm
content: wow, that phone line surge propagated nicely!That is a decent damage list.When it comes to connected medical devices, it is a must that all devices have galvanic isolation from the rest of the private network, so something like this is usually used:Your story reminded me of a few cases I heard during dial-up era, where people had their computers damaged by a surge through the phone line during thunderstorms.

author: Ian.M
author_rank: Super Contributor
timestamp: November 30, 2016, 01:47:25 pm
content: During a lightning induced surge, you are likely to get a significant voltage differential between systems grounded to different grounding rods. Therefore if the phone entry point and GDT arrestor is far from the power entry point, it can be very difficult to protect the modem and thus the network. You could fit a whole house ADSL splitter after the incoming phone GDT and run the ADSL signal to the modem via a GDT grounded to the power entry point grounding rod, to minimise the risk of an excessive potential difference between ADSL wiring and the power wiring ground, but that may not meet local code. Otherwise the modem must be treated as sacrificial.

author: madires
author_rank: Super Contributor
timestamp: November 30, 2016, 02:34:11 pm
content: Quote from: BBBbbb on November 30, 2016, 01:29:53 pmTypical ethernet magnetics are rated for 1500V isolation. They already provide galvanic isolation, just saying. But they are not suited for medical grade isolation.Regarding using a TVS I like to note that a standard TVS got a high capacitance (a few nF), which creates a low pass filter. There are special data line protection ICs hiding the TVS' high capacitance by diodes. Common protection adapters got those plus GDTs.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 30, 2016, 04:39:32 pm
content: Quote from: Ian.M on November 30, 2016, 01:47:25 pmJust get a cheap but good plug in surge protector with phone line protection and call it done.