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I've been investing in some new surge protectors lately – a fraught process at best given the difficulties of comparing model and brand quality. Things were even trickier when looking into ethernet (rj45/cat5e) surge protectors, so I fell back on Tripp Lite since they seem to be lots of folks' favorite brand. I just got off the phone with a Tripp Lite representative who told me all of their ethernet protection products cap out at 100Mbps, and they expressed skepticism that there was anything reliable and faster on the market.

Is there:

  1. An electrical reason surge protector speeds don't go higher?
  2. Not enough demand to justify faster protectors because people don't typically protect ethernet connections or protect them through other means?
  3. Something else I've not considered?
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3 Answers 3

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There are TVS solutions that cover not only Gbit Ethernet, but even faster standards like HDMI 2.x and USB3.

Not sure where the Tripp-Lite guy is getting his info, but here's an appnote from Semtech for Ethernet protection: https://interferencetechnology.com/defending-ethernet-ports-from-electrical-transient-events/

tl; dr: they offer the RClamp3374N for Gbit Ethernet.

Higher speed standards get fussy about the TVS diode capacitance affecting the eye diagram too much. HDMI2.x in particular is sensitive to this, so the TVS must be chosen with care.

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  1. No, there is no reason, and in fact faster do exist - available even from Tripp-Lite, so maybe you should be very sceptical about their salesperson.

  2. No, it's usually just that people run Ethernet only inside their house, so unless you have Ethernet running between two buildings, you have little reason to protect Ethernet from surges that come from outside due to lightning strike or such events.

  3. Yes - why do you need Ethernet surge protection to begin with - it's an isolated interface, so most of the time items inside your house do not need one.

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  • \$\begingroup\$ Re 3: are you suggesting that so long as switches and routers are themselves powered on surge protectors, that ethernet connected devices are isolated from surges over ethernet? For example, say I had a router not on a surge protector and connected over ethernet to a switch which was powered behind a surge protector, which was in turn connected to a computer on a surge protector. In the event of a surge, the router is unprotected and so a surge could reach the switch over ethernet, but not the computer beyond? \$\endgroup\$
    – fedora
    Aug 18, 2021 at 18:27
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    \$\begingroup\$ @fedora If it is necessary to consider such situations, fibre connections would eliminate those problems. \$\endgroup\$
    – Andrew Morton
    Aug 18, 2021 at 19:01
  • \$\begingroup\$ @fedora you would at least have to explain what surges you are talking about. Where would the surges come from? Via mains power - but power supplies are transformer isolated. Via phone line to the modem/router - but the phone line is also transformer isolated. \$\endgroup\$
    – Justme
    Aug 18, 2021 at 19:53
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Something else I've not considered?

Think about what ethernet has that most other data comms don't have; namely, the magnetics: -

enter image description here

They provide surge voltage isolation. Picture from this Farnell data sheet

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  • \$\begingroup\$ Those magnetics aren't perfect: they can have some coupling from large common-mode transient events. The TVS diodes on the PHY side will suppress these. \$\endgroup\$
    – hacktastical
    Aug 18, 2021 at 17:28
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    \$\begingroup\$ Yes, and that's the thing that I believe might be adding to the confusing the op. A lightweight TVS that doesn't upset the data rate due to high capacitance isn't a problem and, it isn't a problem because the majority of the energy of the surge just cannot reach the PHY due to the isolating nature of the magnetics. \$\endgroup\$
    – Andy aka
    Aug 18, 2021 at 18:12
  • \$\begingroup\$ The technical nuance is a bit over my head, so I appreciate your patience helping me sort it out. I think I follow the idea of the magnetics isolating devices over Ethernet. It's easy to find lots of anecdotes from people who had networked devices damaged by surge over Ethernet though. How do such things happen if it's an isolating interface? \$\endgroup\$
    – fedora
    Aug 18, 2021 at 18:20
  • \$\begingroup\$ My own, direct experience (set-top boxes) is that relying on the magnetics to block common-mode fast transients isn't enough - they need suppressors to get the residual energy that manages to sneak through. Magnetics with protection in them were also more expensive / harder to multiple-source than using a separate TVS solution on the PHY side. \$\endgroup\$
    – hacktastical
    Aug 18, 2021 at 18:20
  • \$\begingroup\$ If we are talking about proper surges i.e. indirect lightning strikes then the standard ethernet magnetics will do the job up to a couple of thousand volts. CM fast transients are different and much faster but, they are generally not called or referred to as surges (as per the question title and text). \$\endgroup\$
    – Andy aka
    Aug 18, 2021 at 18:25

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