After my router broke in a thunderstrorm, I am trying to establish surge protection for power lines as well as (this question) for telephone/internet lines.

I found devices such as Tupavco TP302, using gas discharge tubes. It is placed between the TAE wall data outlet and the router. In contrast to others, it has also a grounding cable. I thought a grounding cable would offer additional security to get rid of surges, but...


  1. Is this truly beneficial? Isn't it enough to shortcircuit the 2 wires with the potential difference? Or is it simply "faster" for the current to escape via a (thicker) grounding cable? (The attached grounding cable is quite thin, I'd say less than the standard 1,5 mm for AC wiring :-(
  2. Could it be even a disadvantage? What about surges that might possibly enter via ground, especially if the telecommunication line is not connected to the "same" ground (main grounding terminal). Could temporary transients (as explained here) between the main grounding terminal of the house ("Potentialausgleichsschiene", AC power for router) and telecommunication ground (data lines) after an (indirect) flash of lightening rather cause destruction?
  3. Would ignoring the grounding wire of the data surge protector (i.e. not attaching it to ground) result in a disadvantage compared to a device that simply does not have a grounding cable in the first place? (I assume the grounding cable simply the center tap of the gas discharge tube(s)?)
  4. Most important: Would it be safe to connect the grounding cable of the data surge protector to AC power ground (PE contact, e.g. via a plug where I connect only the grounding (PE ) wire?)** I am hesitating to touch AC power outlets/plugs. Commercial grounding plugs I found so far have 1 MOhm resitance (necessary for EMD protection while touching electronics), thus not suitable. Alternatively I thought of iron water/heating tubes, but would have to determine resistance/impedance to earth and possibly introduce a "third" ground potential. Better than nothing?

AC power network is most likely TN-C in Germany as far as I found out so far.


I found the following schematic drawing (Tupavco website) of a rack-mountable version of the device (I can only guess it uses the same technique as my not-rack-mounted device), showing GDT betweeen paired lines, with the center tap connected to ground:

enter image description here


2 Answers 2


The ground cable should be connected to AC Earth (aka Ground) else it will not work. The goal is to divert transient current to Earth. Not between lines, as shown on the diagram.

Transient can indeed come from the Earth line, but it's rather rare, if not exceptional, and, in this case no device will be able to protect your installation anyway.

You can attach the Earth cable inside a wall plug or any Earth terminal block. Make sure to turn off the circuit braker before opening the wall plug.

Also, and this is very important: Check the Earth connection. The fact that a Earth cable is present doesn't mean it's properly connected.

  1. Yes. Having a suppressor just between wires wouldn't suppress the common mode transient, present in "both" wires. I said both, because the ethernet has 8 wires, so it makes further complicated to have supressors placed in between each wire.

  2. I don't think so. Where does your ISP cable comes from?

  3. Without connecting the ground wire, the protection won't work. There is no schematics or photo of the centrally positioned GDT, so these are only guessings.

  4. "Commercial grounding plugs I found so far have 1 MOhm resitance" . It could be that you are wrong? 1M resistance is for some ESD mats, bracalets - this is not grounding. Grounding is a direct connection to PE.

  • \$\begingroup\$ @Marco Buršič: ___[ad 2] ISP cable: cannot track physically and no answer from landlord. Most likely earth cable (common in Germany, connot see any "air" cable), and likely not attached to main grounding terminal. Is this what you were asking by where the ISP cable comes from? ___[ad 3] I added a schematic drawing of the electric construction of the SPD. May I ask to explain/link why the center tap is necessary? (sorry for my ignorance). ___[ad 4] Yes, 1 MOhm for ESD protection only, not proper grounding - this is why I cannot use it and am looking for a save alternative. \$\endgroup\$
    – Martin
    Commented Sep 1, 2019 at 14:21

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