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Surge Protector for TN-CS Network: Installation, Recommendations & 3/4-Pole Options

paweldre 30939 12
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  • #1 16836575
    paweldre
    Level 9  
    Hello,
    I have a question about the surge protector, which is planned to be installed in the RG, which parted with modernization.
    The type of home network is TN-C - connect e NN braid (?) (L1, L2, L3 and PEN) However, behind the meter in RG there is a division on the PE strip into N and PE, and the distribution point is grounded with a 16 mm2 PE conductor (stranded) Earthing value after 4.5 Ohm measurement (in Poland - ohms) . -> GSU
    From the distribution points of this network is TN-CS later in the installation.
    An electrician will recommend me to an electrician, but I would like to ask what colleagues would use in such a system. There are many manufacturers, different prices, so any optimal solution?
    There are 3 and 4 fields and various opinions I have read, Should TN-CS have 3-pole L1, L2, L3 and the fourth grounding terminal? Is there also to be an N terminal?
    Eg.
    http://www.forumsep.com.pl/viewtopic.php?t=7772
    And so the tasks are divided as to the type of protective.
    I have an idea, please?
    Thank you for reply
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  • #2 16836632
    globus
    Level 24  
    4 poles and no discussion (N are treated normally as phased for many years). In addition, they SHOULD be on a separate connection directly to your earth electrode than the rest of the switchboard cy ". This is most preferably looking at the distribution of voltages in the system when the surge arrester works during a discharge. The voltage drop at the earth electrode - arrester connection does not directly affect the potential of the remaining installation.
    And as for the costs, evaluate it yourself, even if you spend with 500, what is the cost with any losses in home electronics? However, if you do not have one there, is it worth it at all?
    According to me, don't be fooled by the replaceable inserts "Because you can only replace one" and it is "cheaper", and so after a few years it turns out that the producers have stopped producing this model, the other one doesn't fit and you once paid more to have exchangeable and now and yes you have to buy the whole thing again.
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  • #3 16836979
    emigrant
    Level 29  
    paweldre wrote:
    4 and no discussions

    Since the supply network is TN-C, the chapter is in RG and there is also to be SPD there, why do he need the N-PE module? After separation, the PE bus is actually a PEN bus with a separate N. Between the PE bus (PEN) and N there is such a small distance within the switchboard that the N-PE module is not needed here. The SPD for the TN-C system should be used.
    It is different if someone has a PEN division in the connector, or a meter box on the facade, and WLZ to RG is 5-wire and has a few or several meters. Then use SPD for the TN-S system, with the N-PE module, preferably 3 + 1 (with summing spark gap). Then we have galvanic separation of N from PE. There is no possibility of short circuits between N and PE or L and PE.
    paweldre wrote:
    And as for the costs, evaluate it yourself, even if you spend with 500, what is the cost with any losses in home electronics?

    There is no SPD for PLN 500 T1 or T1 + T2. As they are, they should not be on the market because they do not have a cutting off member. For this the author has an overhead connection. The cheapest spark gap T1 + T2 is probably DEHNshield monoblock, the price of which fluctuates around slightly over 1000 zlotys. I think Hager also has something, a DEHNshield clone. It should be cheaper.
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  • #4 16843369
    paweldre
    Level 9  
    Thank you for the reply, but I am surprised by the price. This is even more to ponder, because I do not have such expensive equipment at home and for almost 40 years I have not had experience with surges.
    I also read in a few places about the redundant N-PE module in this system.

    Hager e.g. here:

    https://www.hager.pl/files/download/0/515663_...PL_2014_hager_ochrona_przeciwprzepieciowa.pdf.
  • #5 16843421
    emigrant
    Level 29  
    Equipment is the least important. SPDs are not used to protect equipment, but to limit overvoltage on SPD terminals and to equalize the potential difference in the electrical installation at the time of lightning. Of course, in a sense, SPD is involved in the protection of electronics. I would have added Hager SPA400 unless you have a lightning protection system. From what I see, you can buy a new one for PLN 800, so the price is quite low. A little cheaper than DEHNshield. You have an outdoor connection, so T1 should not be varistor. I spent over 2000 zlotys on SPD and I don't waste money on the right and left. Mounted and I hope it will never have to work.
  • #6 17113749
    paweldre
    Level 9  
    Hello,

    I still have a question, what effect can the surge protector have on the length of the wire from the grounding terminal in the protector itself to the grounding strip, for example, hoopers? The 16 mm2 cable will be connected individually with a length of about 2 m.

    I don't know if it interprets the instructions correctly - SPA400 Hager instruction in combination.
    Should the cable through which this connection will be made be additionally insulated e.g. in a tube in case of a high surge current?
    Attachments:
    • ID1_SPA400_6S5106D-1.pdf (448.03 KB) You must be logged in to download this attachment.
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  • #7 17115364
    Jacek Rutkowski
    Level 28  
    In what language, buddy paweldre You are writing? It doesn't have much in common with Polish ...
    Where did you get this photo from? Some comment is probably there and probably it is about separating the grounding conductors of the protector from others and fixing them in case of discharge. High current during the discharge is able to pull the cable out of the plaster or also stir in the switchboard when it is laid with excess.
  • #8 17116085
    lukiiiii
    Level 29  
    Is there a household way to build a surge protector? Anyone got such a miracle undressed? What's inside?

    Varistor and spark gap?
  • Helpful post
    #9 17117059
    michcio
    Electrician specialist
    paweldre wrote:
    I still have a question, what effect can the surge protector have on the length of the wire from the grounding terminal in the protector itself to the grounding strip, for example, hoopers? The 16 mm2 cable will be connected individually with a length of about 2 m.


    From the point of view of limiting surges coming to the devices from the electrical installation side, it is important that the cables connecting the protected installation with the limiter and the limiter with the protective rail of the switchgear in which it is installed are as short as possible. The cables connecting the SPD to the installation are best eliminated by using the V connection, while the limiter should be connected with the shortest possible cable to the switchboard PE busbar. This connection will ensure maximum voltage reduction that will occur in the installation between live conductors (L, N) and PE.
    The second cable should be connected to the equalizing rail SPD. The length of this cable is particularly important if other installations are connected to the equipotential rail, especially telecommunications and antenna (together with surge arresters for these installations), because it will reduce the value of overvoltage between these installations and the electrical installation (this is especially important for connected devices to more than one installation at a time). The length of the cable connecting the equalizing bar to the ground is of lesser importance here. If the conditions require the use of very long (> 0.5m, in extreme cases> 1m) cables connecting SPD with the expansion rail, it is best to move this rail closer to SPD or SPD move closer to the rail (obviously easier to maneuver the rail than the entire switchboard in which the SPD is ).

    paweldre wrote:
    I don't know if it interprets the instructions correctly - SPA400 Hager instruction in combination.
    Should the cable through which this connection will be made be additionally insulated e.g. in a tube in case of a high surge current?


    This is not about insulation (as @jacek Rutkowski has already mentioned), but about proper cable fastening. Longer (according to this manual> 20cm) loose sections of wire are exposed to high electrodynamic forces when passing surge currents (speaking colloquially - they will dance), so they can even be pulled out of the terminals of the devices, so they need to be mechanically fastened. This applies to all conductors, where we expect the surge current to flow, i.e. mainly those connecting the arrester with the installation, with the rails and connecting the equalizing rail with the earth electrode.
  • Helpful post
    #10 17117200
    emigrant
    Level 29  
    A longer cable> 1 m may be used between the ground terminal in the SPD and the equalizing (or grounding) rail, provided that it is flat (tape). It's about the inductance of the round conductor.
  • #11 17118617
    paweldre
    Level 9  
    Thank you for reply
    Is a steel tape at stake, e.g. in the form of a hoopkin not pulled above for switchboards?
    Regards,
  • Helpful post
    #12 17118633
    emigrant
    Level 29  
    If the cooper is too short, extend it "by tab". Drill holes at 3-4 points, e.g. with a 10-bit drill, and screw tightly preferably with a self-locking nut. The connection should be strong and stable. That's probably the subject.

Topic summary

✨ The discussion revolves around the installation of surge protectors in a TN-CS network, specifically addressing the necessity of a 3-pole or 4-pole configuration. Participants emphasize the importance of using a separate connection for the earth electrode and the potential redundancy of an N-PE module in this setup. Recommendations include using surge protective devices (SPDs) suitable for TN-C systems, with suggestions for models like Hager SPA400 and DEHNshield. The conversation also touches on the significance of minimizing cable lengths between the surge protector and grounding systems to reduce inductance and improve surge protection efficiency. Concerns about the grounding connection's length and insulation requirements are raised, along with practical advice on ensuring strong and stable connections.

FAQ

TL;DR: For TN-C to TN-C-S homes with overhead supply, budget ~PLN 1,000 for a T1/T2 SPD; “There is no SPD for PLN 500 T1 or T1+T2.” [Elektroda, emigrant, post #16836979]

Why it matters: This FAQ helps homeowners choose and wire the right SPD to avoid dangerous overvoltages in mixed TN-C/TN-C-S installations.

Who this is for: DIY-savvy homeowners and electricians planning surge protection in TN-C/TN-C-S dwellings with meter-board PEN split.

Quick Facts

Which SPD topology should I use in a TN-C supply with PEN split in the same board?

Use an SPD for TN‑C at that board; the N‑PE module is not needed there. If the PEN split were far upstream with a 5‑wire run, then you’d choose an SPD for TN‑S with an N‑PE module. [Elektroda, emigrant, post #16836979]

Do I need a 3‑pole or 4‑pole SPD in TN‑C‑S?

Use a 4‑pole device. The neutral is treated as a phase in such protection schemes, which simplifies clamping between all conductors and PE. As one expert put it, “4 poles and no discussion.” [Elektroda, globus, post #16836632]

Should I protect the N conductor after a local PEN split?

When the PEN is split to N and PE in the same switchboard that hosts the SPD, the dedicated N‑PE module is redundant. Select an SPD intended for TN‑C at that location. [Elektroda, emigrant, post #16836979]

What should I budget for a main T1/T2 SPD?

Expect roughly PLN 800 for a spark‑gap T1 like Hager SPA400; T1+T2 monoblocks can cost more. “I would have added Hager SPA400… price is quite low.” [Elektroda, emigrant, post #16843421]

Does earth resistance matter (e.g., 4.5 Ω measured at the GSU)?

A low‑impedance, direct earth path is critical. Route the SPD to a dedicated earth electrode connection to limit voltage rise in the installation during discharge. This minimizes potential differences when the SPD operates. [Elektroda, globus, post #16836632]

How long can SPD leads be without hurting performance?

Keep all SPD leads as short as possible. Use a V‑connection to eliminate extra length. Fasten any loose sections over 20 cm to withstand electrodynamic forces. If leads exceed ~0.5–1 m, relocate the SPD or equipotential bar. [Elektroda, michcio, post #17117059]

Do I need to sleeve or insulate the SPD earth cable?

No. Focus on mechanical fastening and minimal length. High surge currents can make long, loose wires “dance” and rip from terminals, so secure them properly. [Elektroda, michcio, post #17117059]

Can I use flat steel or copper tape for a long earth run?

Yes. For runs beyond about 1 m, use flat tape to reduce inductance compared with round conductors. This improves clamping performance during surges. [Elektroda, emigrant, post #17117200]

How do I extend a short copper strap to reach the bar?

Extend it “by tab.” Overlap the straps, drill 3–4 holes, and bolt tightly with self‑locking nuts for a strong, stable joint. [Elektroda, emigrant, post #17118633]

Is a DIY surge protector realistic, and what’s inside commercial SPDs?

Commercial SPDs use spark gaps and/or varistors with coordinated elements. For overhead-fed mains, choose a T1 spark‑gap type; avoid varistor‑only T1. DIY is unsafe and not recommended on mains. [Elektroda, emigrant, post #16843421]

When should I use a 3+1 SPD with an N‑PE module?

Use 3+1 (with summing spark gap) when the PEN is split upstream, and a 5‑wire feeder runs several meters to your board. It provides galvanic separation of N from PE and avoids N‑PE shorting risks. [Elektroda, emigrant, post #16836979]

Are replaceable SPD cartridges worth it long‑term?

Be cautious. Models change, and replacements may become unavailable, forcing full replacements later despite higher initial costs for swappable inserts. [Elektroda, globus, post #16836632]

Overhead vs. underground supply: does it change SPD choice?

Yes. With overhead service, choose a T1 spark‑gap front end (e.g., SPA400). Spark gaps handle high-energy impulses better than varistor‑only T1 units at the service entrance. [Elektroda, emigrant, post #16843421]

What is an SPD, in simple terms?

A Surge Protective Device limits overvoltage by diverting surge current to earth and equalizing potentials between conductors and PE during lightning or switching events. It protects people and equipment indirectly by clamping dangerous voltages. [Elektroda, emigrant, post #16843421]

Quick how‑to: wire a main SPD for best effect

  1. Mount the SPD close to the main PE/N bars; plan a V‑connection to phase, neutral, and PE.
  2. Keep all leads short and straight; mechanically fasten any segment over 20 cm.
  3. Bond to the equipotential bar; minimize length or move the bar closer. [Elektroda, michcio, post #17117059]
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