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Does this type of lightning/surge protection on ethernet couplers depend on a connection to ground through the shielding of the connected ethernet cables? Considering UTP (unshielded twisted pair) is used in most places, this would be useful to know before deciding on what type of coupler to get.

How does TVS (transient voltage suppression diodes?) protection work, and is it worth it?

adatum
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  • "Anti-thunder" (in the image) is a useless capability. What is "thunder damage"? Is there a language translation problem? – sawdust Apr 02 '23 at 00:45
  • @sawdust Yes, clearly a language issue. It's about surge protection. I doubt any such device can protect against direct lightning strikes. As for what it does or how it's wired.. well that is the question. – adatum Apr 02 '23 at 01:01
  • "*I doubt any such device can protect against direct lightning strikes.*" -- There is nothing that can protect a connection after a direct strike. Remember, there is so much voltage that lightning can use air as a conductor. I've read about unplugged devices getting fried; apparently the strike jumped from the outlet to the plug. I recall industrial xDSL products needing similar "lightning protection" on the phone wires for UL approval. The other end would be connected to chassis ground. – sawdust Apr 02 '23 at 01:16
  • @sawdust Yes, I think the "lightning protection" is mostly a marketing term referring to some form of surge protection. Hence the quotes in the title. But the questions remain: does this protection require shielded/grounded ethernet cables, and even then does it provide any appreciable benefit, as well as does it introduce any disadvantages? – adatum Apr 02 '23 at 01:40

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A lightning strike creates a magnetic field with a high rate of change which induces voltage into any loops made of conducting material. It works like a transformer. The primary coil of this transformer is the lightning bolt itself, and the secondary is any cable loop in the vicinity.

In this case the cable loop could be something like:

Mains - Switch power supply - Ethernet switch - Ethernet cable - Desktop PC - Mains

...but really, any cable loop will be hit with induced voltage, which means devices which are at the intersection of several networks (electrical grid, telephone, cable TV, ethernet, etc) have a chance of being part of these loops.

The larger the loop (in terms of surface area) the higher the voltage. So the loop created by two twisted wires inside a cable receives a very small voltage because the wires are close together, whereas the example loop above will receive a much higher voltage, because the cables involved can be far apart.

It is not possible to prevent this induced voltage from happening when lightning strikes. What the protection device does is provide an easy path for the surge current to flow, so it flows through the protection device and not through the sensitive device it's supposed to protect. The usual way is to use a TVS diode or other voltage limiter between the wire to be protected and the Earth conductor.

In the example loop above, if the devices are equipped with surge protectors this means the loop becomes:

Earth - Switch power supply - Ethernet switch chassis - TVS - Ethernet cable - TVS - Desktop PC chassis - Earth

So the current goes from the cable through the TVS, the chassis, then Earth, and closes the loop through Earth back to the cable. In both cases it doesn't go through the network interface chips at both ends of the cable.

However the surge protector in the question doesn't have any connection to Earth... so the only thing it can do is protect against high voltage between the wires in the Ethernet cable (which never happens) but it can do nothing against high voltage between the cable and Earth. So it's going to be completely useless.

This has nothing to do with the shield on the cable: without a connection to Earth, a surge protector can't sink the surge current to Earth to protect sensitive devices.

bobflux
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  • Are you saying that the TVS diodes in those couplers are useless? At least for UTP? I'm not sure how the TVS are wired. However as for shielded cables, those are supposed to be grounded at the ends, so that would be the path to ground, no? – adatum Apr 01 '23 at 22:08
  • The surge protection might be connected to signal ground, so it may not be "*completely useless*". – sawdust Apr 02 '23 at 00:40
  • @sawdust I'm not too familiar with this, but I believe twisted pair like ethernet uses differential signals between pairs of wires, and not relative to any reference ground. Is there even any wire that is considered "signal ground" in ethernet? I doubt. – adatum Apr 02 '23 at 01:12
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    @adatum -- Oops, you're correct on both counts. Wrote that comment too quickly. – sawdust Apr 02 '23 at 01:23
  • @adatum "*those are supposed to be grounded at the ends*" -- An EE grad from CalTech told me (a long time ago) to ground only one end of the shield rather than both ends. The practice seems to vary according to cable & signal type. See https://www.cablinginstall.com/connectivity/article/16465477/grounding-shielded-cable – sawdust Apr 02 '23 at 01:33
  • @sawdust The issue with grounding at one or both ends is still unclear, but seems to be about the potential for ground loops. However, an expert-based article referenced in another SU answer suggests it is mostly a non-issue. I'm not about to get into this famous internet debate here, and hopefully just focus on the title question. FYI: article: https://www.cablinginstall.com/home/article/16467568/the-myths-and-realities-of-shielded-screened-cabling SU answer: https://superuser.com/a/1295287/933126 – adatum Apr 02 '23 at 01:46
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    @adatum For UTP, useless. For STP, it depends if the shield is connected. There is no signal ground in Ethernet, it's all differential. It is transformer-coupled at both ends so equipment will only be damaged if the high voltage due to lightning exceeds the transformer's insulation and it arcs over the windings and into the chip. – bobflux Apr 02 '23 at 05:12
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    If shielded connectors are used then STP shield will be connected to chassis of receiving device, but many devices are not earthed. In this case if the TVS are between the ethernet wires and shield they could work. I wouldn't use a surge protector that depends on so many conditions to work... – bobflux Apr 02 '23 at 05:15
  • I guess if the equipment is expensive enough to protect it, better use a 10€ surge protector from a reputable manufacturer (with Earth) instead of a 1€ device from aliexpress XD – bobflux Apr 02 '23 at 07:43
  • @bobflux Exactly, most routers use two prong plugs. The issue isn't one of cost, since the TVS models are only slightly more expensive, but nowhere does anyone say that shielded connectors are necessary, though I don't see how surge protection could work without some ground. Also curious whether they introduce any downsides. But in any case I'm thinking to skip the TVS coupler models if they don't offer a benefit. – adatum Apr 02 '23 at 08:19
  • Well if the router is not grounded, and there are TVS between signal lines and shield, and shield is connected to routed chassis ground, then there won't be high voltage between signal lines and router ground, so this router port will survive. But the surge will pass through the chassis to all the other cables, so all the other ports need to be protected too, and the stuff at the other end XD much simpler to dump the surge into Earth – bobflux Apr 02 '23 at 08:33
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    @bobflux Certainly, if the goal is surge protection, then something with a separate ground connection seems better. The point of my question is to know whether a TVS-equipped coupler, considering the marginal cost, has any benefits (and/or drawbacks) that should be considered when shopping for a coupler for UTP ethernet cables. It appears the answer is no. – adatum Apr 02 '23 at 08:41