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Induction loop, AC, DC protection and other questions related to PV installation

Spajder_PL 38019 42
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How should a PV installation be wired to avoid induction loops, and what grounding, DC surge protection, and AC/DC protection arrangement should it have?

Avoid induction loops by routing the + and − conductors of each string together, side by side or in the same conduit; if the layout forms a loop, reroute one conductor alongside the other or use a V connection so the protection branch disappears [#18357126] [#19007328] [#20327705] [#18372514] On the protection board, one reply said the AC side with type 1+2 arresters looked OK, but the DC side overvoltage protection was not visible and may be missing unless it is built into the Fronius Symo 12.5 inverter; the same reply also questioned the C20A four-pole breaker and the 100 mA RCD and said AC and DC circuits should be separated by a marked partition [#18356954] For the contractor complaint, the thread advised comparing the installation with the agreed offer/specification and asking the installer to justify any deviations, including DC arresters, separate AC/DC switchgear, loop removal, and panel grounding/equipotential bonding [#18364317]
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  • #31 19504015
    StaruchPl
    Level 11  
    Posts: 111
    Rate: 11
    Hello. I am just trying to install a PV plant and read a bit about induction loops. I do not know if I have planned the cable routing well, so there are two versions of the connection in the attachment. According to me, both should be correct, but I prefer to check with more experienced colleagues. The assembly of the panels will be on the so-called bridges on the roof are made of trapezoidal sheet metal, so the bridges will be interconnected with a PE cable and then "grounded". In the drawings, PE is marked in yellow. All cables will be run side by side, tied together with cable ties and attached to the load-bearing structure. I am asking for your opinions. Greetings.

    Induction loop, AC, DC protection and other questions related to PV installation Induction loop, AC, DC protection and other questions related to PV installation
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  • #32 19504028
    sq9fmc
    Level 29  
    Posts: 963
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    Both versions are correct as long as the DC voltage wires are close to each other.
  • #33 19504029
    StaruchPl
    Level 11  
    Posts: 111
    Rate: 11
    OK - thanks for the answer
  • #34 19628719
    sz.lukas
    Level 10  
    Posts: 10
    Rate: 1
    Hello, the Hyundai PV panels user manual shows how to connect the panels to each other, won't there be a problem with the induction loop in this case?
    Can it be combined according to the manufacturer's recommendations?

    Induction loop, AC, DC protection and other questions related to PV installation
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  • #35 19628730
    StaruchPl
    Level 11  
    Posts: 111
    Rate: 11
    In my opinion, this is an obvious induction loop. I had a similar dilemma to you and as a consequence I applied the solution as shown in my drawing (Version II). It is true that with my solution more solar cable comes out, but for safety, I think that it is better to add a few zlotys. In my installation, all the cables shown in the diagram were run next to each other and fastened together with UV-resistant cable ties.
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  • #36 19629719
    Cez166
    Level 1  
    Posts: 1
    Hello, I plan to install on the ground 2x 6 panels 340W (~ 4kW) tied into one string. A request for advice from more experienced practitioners on the subject.
    1. The set will be about 8-10m from the wall of the house with the inverter (~ 10-12m of cable, ground). I wonder how to connect the DC box on the structure with the inverter at home, or with 4mm2 or 6mm2 PVC cables in an additional sheath in arot or a cable dedicated to the ground (max current ~ 9A)?
    2. Is it necessary to provide a second DC lightning protection at the inverter with such a DC cable length?
    3. 3-phase inverter max. Current ~ 6A / phase distance ~ 8m from the main switching station in the house to which I will connect. In the inverter manual they write that at such a distance, a 5x2.5mm2 cable can be used, but I wonder if 5x4 mm2 will not be better.
    4. Request for opinions: should we give pv fuses in the DC box (what they protect in practice, or are they just a disconnector between the PV and the rest for some service work) and when do we use a 100mA 3-phase differential behind the inverter?

    Thank you in advance for your help
    Adam
  • #37 19629925
    kosmos99
    Level 38  
    Posts: 4188
    Help: 338
    Rate: 816
    Cez166 wrote:
    1. The set will be about 8-10m from the wall of the house with the inverter (~ 10-12m of cable, ground). I wonder how to connect the DC box on the structure with the inverter at home, or with 4mm2 or 6mm2 PVC cables in an additional sheath in arot or a cable dedicated to the ground (max current ~ 9A)?


    It is best to connect the inverter together with the protection at the construction site, only AC lead through the earth cable.
    However, if the decision was to place the inverter in the building, then send DC to it via a ground cable, PV cables in arota are an average idea.

    Cez166 wrote:
    2. Is it necessary to provide a second DC lightning protection at the inverter with such a DC cable length?


    I understand you mean overvoltage? If the inverter is built, one DC surge voltage will suffice.

    Cez166 wrote:
    3. 3-phase inverter max. Current ~ 6A / phase distance ~ 8m from the main switching station in the house to which I will connect. In the inverter manual they write that at such a distance, a 5x2.5mm2 cable can be used, but I wonder if 5x4 mm2 will not be better.


    The larger the cross section, the better.

    Cez166 wrote:
    4. Request for opinions: should we give pv fuses in the DC box (what they protect in practice, or are they just a disconnector between the PV and the rest for some service work) and when do we use a 100mA 3-phase differential behind the inverter?


    Depending on the manufacturer of the inverter and its requirements.
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  • #38 19632269
    sz.lukas
    Level 10  
    Posts: 10
    Rate: 1
    StaruchPl wrote:
    In my opinion, this is an obvious induction loop. I had a similar dilemma to you and as a consequence I applied the solution as shown in my drawing (Version II). It is true that with my solution more solar cable comes out, but for safety, I think that it is better to add a few zlotys. In my installation, all the cables shown in the diagram were run next to each other and fastened together with UV-resistant cable ties.


    Thanks for the answer, in my opinion, too, but often on forums there are answers like use search, or look at the manufacturer's documentation. On the contrary, I would say that the documentation and manual are treated as sacred, so it is surprising that there is an evident error here.
    Unless this induction loop is not that dangerous, also in the opinion of the producers.
    On the other hand, if I do not do as the manufacturer recommends, will the 25-year warranty be respected by him?
    Maybe someone from the forum who works with it will comment on a daily basis.

    greetings
  • #39 19633212
    MichałS
    Level 35  
    Posts: 2696
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    Rate: 678
    sz.lukas wrote:
    will the 25-year guarantee be respected by him?
    Maybe someone from the forum who works with it will comment on a daily basis.

    greetings

    Forget that in 25 years any of the current producers will exist. Just see how they are changing today. Apart from that, the panels cannot withstand that much. 10-year-olds brought from southern Europe simply fall apart (and 10 years ago everything was more solid).
  • #40 19633624
    sz.lukas
    Level 10  
    Posts: 10
    Rate: 1
    MichałS wrote:
    sz.lukas wrote:
    will the 25-year guarantee be respected by him?
    Maybe someone from the forum who works with it will comment on a daily basis.

    greetings

    Forget that in 25 years any of the current producers will exist. Just see how they are changing today. In addition, the panels do not withstand that much. 10-year-olds brought from southern Europe simply fall apart (and 10 years ago everything was more solid).


    This is what I wrote about these 25 years, but even after a year someone may question the performance, because it is not in accordance with the manual.
  • #41 19946169
    gingordon
    Level 11  
    Posts: 25
    Help: 1
    Rate: 3
    Induction loop, AC, DC protection and other questions related to PV installation

    Hello, colleagues, I am building a PV installation using solar edge and optimizers.
    do not comment, please, choose the number of slopes and the distribution of panels on the roof ...
    Please assess whether the designed string is safe and whether there are no induction loops.
    Are such connections safe, can they remain or something needs to be changed?
    I assume that I will pass the and - cables and the earth electrode in one conduit.

    The distance from the last panel to the inverter in the garage is approx. 25 m
    6mm2 cables and 16mm2 earth electrode
  • #42 20327577
    klubcoloseum
    Level 1  
    Posts: 1
    Hello, is this link correct? Induction loop, AC, DC protection and other questions related to PV installation
  • #43 20327705
    3301
    Level 34  
    Posts: 2100
    Help: 224
    Rate: 868
    Yes, only the wires of one circuit need to be run together
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Topic summary

✨ The discussion revolves around concerns related to photovoltaic (PV) installations, specifically focusing on induction loops, protective equipotential bonding, and surge protection. The main inquiry addresses the significance of induction loops in PV systems, referencing a recommendation from Longi Solar that inadvertently creates such loops. Participants discuss the necessity of protective bonding, the installation of surge arresters when the distance between panels and inverters exceeds 10 meters, and the implications of not adhering to standards like PN-EN 61173:2002 and PN-EN 50539-11. Various responses highlight the importance of avoiding induction loops, the correct placement of surge protectors, and the need for proper grounding of panels. The conversation also touches on the technical aspects of wiring and the potential risks associated with improper installations.
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FAQ

TL;DR: A 12-15 m DC run without extra surge protection violates EN 50539-11, “add a limiter at the panels” [Elektroda, Spajder_PL, post #18356639] Experts warn: “keep wires short” [Elektroda, Spajder_PL, post #18371751] Fix loops, add SPDs, and separate AC/DC to stay safe.

Why it matters: Correct routing and protection prevent lightning-induced surges, fires and warranty disputes.

Quick Facts

• EN 50539-11 requires an extra DC SPD when array-inverter distance > 10 m [Elektroda, Spajder_PL, post #18356639] • EN 62305 limits SPD lead length to ≤ 0.5 m to curb inductive voltage [Elektroda, Spajder_PL, post #18371751] • Typical 4 kW ground-mount string current: ~9 A; use 4–6 mm² Cu cable [Elektroda, Cez166, post #19629719] • Type 1+2 AC SPD plus C-curve 20 A breaker meets Polish practice [Elektroda, theo33, post #18356954] • DC connector faults cause 29 % of PV fires [Fraunhofer ISE, 2020]

What is an induction loop in a PV installation?

An induction loop is any closed wiring path that encloses area. A lightning pulse or switching surge generates a magnetic field; the loop acts like an antenna and induces dangerous voltages in the string [Elektroda, MichałS, post #18357126]

How do I wire modules to avoid creating a loop?

  1. Run positive and negative conductors together from the first to the last module. 2. Return the unused conductor alongside the first, not around the array. 3. Tie both conductors every 0.5 m to keep them touching. This V-routing removes the enclosed area and the loop [Elektroda, wello, post #19007328]

Do manufacturer diagrams that cross strings break standards?

Yes. EN 62305-3 states that outdoor circuits must avoid closed loops; following a diagram that forms one conflicts with the lightning-protection part of the standard, even if the manual allows it [Elektroda, Spajder_PL, post #18362654]

When must I add a second DC surge arrester near the panels?

If the cable between the array and inverter exceeds 10 m, fit a Type 2 DC SPD at the array while keeping the inverter SPD unchanged [Elektroda, Spajder_PL, post #18356639]

How short must the leads between SPD and PE bar be?

EN 62305 limits each lead (phase–SPD and SPD–PE) to 0.5 m. Longer leads increase residual voltage and may void protection [Elektroda, Spajder_PL, post #18371751]

Should AC and DC circuits share a single enclosure?

No. Separate, labelled compartments prevent inadvertent mixing and keep clearances consistent with IEC 60364-7-712 [Elektroda, theo33, post #18356954]

Do I need to ground every panel or only the mounting frame?

Most panel manuals require bonding each frame to the mounting structure, which itself must connect to the main earthing bar. Individual grounding straps satisfy this and improve lightning current sharing [Elektroda, Spajder_PL, post #18362654]

Are DC disconnects the same as DC surge arresters?

No. Disconnects isolate the array for maintenance; surge arresters (SPDs) clamp transient overvoltage. Mersen CUS101HEL shown in the thread is a fuse/disconnector, not an SPD [Elektroda, Spajder_PL, post #18356917]

What cable size should I run from the array to an indoor inverter?

For up to 9 A string current and 12 m length, use 4 mm² Cu underground cable; choose 6 mm² if voltage drop must stay below 1 % or if future expansion is planned [Elektroda, Cez166, post #19629719]

Will ignoring the wiring diagram void my 25-year panel warranty?

Manufacturers can refuse claims if installation deviates from their manual, but many firms disappear before 25 years [Elektroda, MichałS, post #19633212] Keep photos and a commissioning report to defend a claim.

What common failure causes PV fires, and how can I avoid it?

29 % of PV fires start at poorly crimped or mismatched DC connectors [Fraunhofer ISE, 2020]. Use original MC4 parts, torque to spec, and inspect yearly. An edge-case shows string fires even at 600 V when connectors were wet and loose [Elektroda, BikeBarian, post #19326528]
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