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Best Ground Cable for 3-Phase PV System: 9kWp, 30m Length, AC & Microinverters Usage

mechagodzillakontra 34026 31
Best answers

What cable cross-section should I use for a 3-phase AC line from microinverters over about 30 m for a 9 kWp PV installation?

Use a 5×6 mm² cable; it was stated to be sufficient with plenty of margin for three single-phase microinverter groups of about 3 kWp each over 30 m [#17774790] Another reply said the minimum is 5×2.5 mm² and the practical optimum is 5×4 mm², with anything larger mostly wasting money unless you specifically want less voltage drop [#17775810] For a 3-phase inverter, 5×2.5 mm² was also described as enough, but a thicker cable can make sense if the network voltage is already high and you want to avoid inverter shutdown from overvoltage [#17750178] Several replies favored copper over aluminum for reliability at the connectors and to avoid oxidation issues [#17776113]
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  • #1 17733810
    mechagodzillakontra
    Level 8  
    3 phases. Length approx. 30 m. The lower installation power is approx. 9kWp. It's about AC because it is installed on microinverters.
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  • #2 17736371
    theo33
    Level 27  
    With even production, the current would be about 13A, so a 16A protection would be enough, with micro inverters which are single-phase devices and the uniformity may not be maintained, and in addition, it is possible to connect at least two (for three probably the pre-meter will be too small) to one phase, I would suggest min. 5x4 or even better one step higher.
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  • #3 17750178
    grzegorz dob.
    Level 20  
    5x2.5 is enough for a 3-phase inverter. using a thicker cable makes sense if you want a very low voltage drop on the cable. measure what voltage you have in the network, if above 245v, it may be justified to use a cable with a larger cross-section because when the inverter is working, the voltage on the inverter cannot increase above 253v (the inverter will turn off). if you have up to 245v there will be no loss of 8v on a 2.5mm? cable with 30m of cable. The use of a cable with a larger diameter is economically unjustified.
  • #4 17750191
    rtvserwisant
    Level 24  
    I would use the YAKY 5x16 cable, it will come out similar to the YKY 5x2.5.
  • #5 17750345
    grzegorz dob.
    Level 20  
    rtvserwisant wrote:
    I would use the YAKY 5x16 cable, it will come out similar to the YKY 5x2.5.

    I do not see a substantive explanation for this statement. through such statements the forum goes to the dogs.
  • #6 17750791
    chrobry25
    Level 14  
    I also recommend the YAKY 5x16.
  • #7 17774755
    mechagodzillakontra
    Level 8  
    So again. Specifically. Three groups of single-phase microinverters, approx. 3 kWp each group. Distance about 30m. What diameter ground cable 5 x how many?
  • Helpful post
    #8 17774790
    prose
    Level 36  
    mechagodzillakontra wrote:
    So again. Specifically. Three groups of single-phase microinverters, approx. 3 kWp each group. Distance about 30m. What diameter ground cable 5 x how many?

    A cross-section of 5 x 6 mm? is sufficient in excess.

    Added after 6 [minutes]:

    http://lumier.pl/kalkulator/
  • #9 17774840
    mechagodzillakontra
    Level 8  
    Thank you very much. This is what I ment. Regards.
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  • #10 17775628
    ACCel
    Level 22  
    But the 5x6 is only copper, which is expensive. Aluminum 5x10 is more profitable.
  • #11 17775810
    grzegorz dob.
    Level 20  
    Have you counted what current will flow through this cable? What kind of counter protection do you have? (C25A) Your whole house is working on this security. In energetic conditions, power allocation up to 16 kW. The minimum cable is 5x 2.5mm?, optimal 5x4mm? above this value is just money wasted. As colleagues above so count, let them use 5x 25mm?, they can connect the whole village to this cable. I wonder if there is a connector in the inverter that will allow you to connect 5x10mm? :D
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  • #12 17775838
    prose
    Level 36  
    ACCel wrote:
    But the 5x6 is only copper, which is expensive. Aluminum 5x10 is more profitable.

    Aluminum is not used in Pv installations for many reasons, and the difference between 4 mm? and 6 mm? of copper is about PLN 2 per meter.
  • #13 17775934
    ACCel
    Level 22  
    prose wrote:
    ACCel wrote:
    But the 5x6 is only copper, which is expensive. Aluminum 5x10 is more profitable.

    Aluminum is not used in Pv installations for many reasons, and the difference between 4 mm? and 6 mm? of copper is about PLN 2 per meter.

    It was the AC side, so it's not a "PV installation" ;) Then you plug it into the network connected with aluminum anyway.
    Looking at the Allegro, the YAKY 5x10 is cheaper than the YKY 5x4, so why overpay?

    Of course, for these 3x3kW 4mm2 with excess it is enough. As long as there were three different phases (N load). Anyway, probably even 2.5mm2 would be ok.
  • #14 17776113
    prose
    Level 36  
    ACCel wrote:
    Looking at Allegro, the YAKY 5x10 is cheaper than the YKY 5x4, so why overpay?

    In order not to have, for example, a problem with the oxidation of aluminum conductors at the connectors, and then problems with the inverter. I had an aluminum one from the workshop, it kept loosening on the connectors until it finally got scorched and that's not one problem I had with the aluminum cable. Better to buy once and have peace of mind.
  • #15 20549813
    michal22michal
    Level 10  
    what cable should be used for 4.5 kw ground installation and foxess t4 g3 inverter? 5x2.5mm2 is enough or does it have to be 5x4mm2?
    pre-inverter on construction - is this a good option?
    the distance from the installation to the house is about 5 m, that's how much will be in the ground.
  • #16 20555751
    grzegorz dob.
    Level 20  
    If you do not intend to expand the installation, 5x2.5 is enough
  • #17 20555809
    adse
    Level 27  
    Wouldn't a thicker cable, e.g. 5x6, be more beneficial from the point of view of switching off the inverter due to the exceeded voltage? With 5 meters underground, it can be assumed that the total length will be about 10-15 meters. The difference in the price of a thin and a thicker cable may be PLN 100, with the cost of the entire installation several thousand.
  • #18 20555918
    michal22michal
    Level 10  
    It can give 5x4mm2 and it will be the optimal solution?
    I will not expand, because I already have one installation of 5.4 kWp, and now I will put the second one on the ground on the construction of 4.5 kWp.

    Inverter under the structure or at home to give?
  • #19 20698235
    likwidatorr1
    Level 12  

    Hello!
    I'm joining the topic ... but I'm wondering if I can use the YAKY 4x35 cable for DC, which I have between the house and the livestock building? The PV installation is 10 m from the livestock building and on this section I would give a traditional dedicated 6 mm cable. And from this point on, I would use an aluminum cable that is already in the ground, about 50 m. This would be more comfortable for a hybrid inverter. One string expected max 400 V DC? Does it make any sense? Please help...

    Regards
  • #20 20698264
    Anonymous
    Level 1  
  • #21 20698296
    likwidatorr1
    Level 12  

    Thank you very much :) I understand that if connected to the network, it will be in accordance with the standards and regulations?
  • #22 20698307
    Anonymous
    Level 1  
  • #23 21033829
    hindoos
    Level 36  
    I am connecting a 2.5kW installation on a flat roof, I have to climb down the wall to the basement level. I want to use YKY / NYY-J 0.6/1kV 5x4 wire to the ground and run it under the insulation - should I additionally use a cable tray or conduit or can the cable itself just be attached to the wall and covered with polystyrene?
  • #24 21033833
    3301
    Level 34  
    Is this cable for the inverter or for DC power from the panels?
  • #25 21033837
    hindoos
    Level 36  
    From microwaves, so AC, three phases.
  • #26 21033887
    3301
    Level 34  
    In places placed on a flammable surface, I would use an additional cover, either from a trough or a conduit, the rest for the wall and under the polystyrene foam.
  • #27 21033905
    hindoos
    Level 36  
    I have never pulled the wire through the conduit (only cables), are the trays left or is there a patent for this? 5x4 may be quite stiff, although I don`t know if I`ve ever had such a cable in my hands :|
  • #28 21034000
    3301
    Level 34  
    I don`t know what it looks like, but I would certainly not cover the entire cable with some kind of cover, e.g.
  • #30 21034832
    k_pec
    Level 34  
    hindoos wrote:
    I have never pulled the wire through the conduit (only cables), are the trays left or is there a patent for this?

    What is your route configuration exactly? Are the conduit/pipe sections straight? or any crackers? I`m thinking about episodes put on wood ( ;) ) or in other places where you would like to have them.
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Topic summary

✨ The discussion centers around selecting the appropriate ground cable for a 3-phase photovoltaic (PV) system with a capacity of approximately 9kWp and a cable length of 30 meters, specifically for use with microinverters. Various recommendations are made regarding cable specifications, with suggestions ranging from 5x2.5 mm² to 5x6 mm² and 5x10 mm², depending on factors such as voltage drop, current flow, and economic considerations. The YAKY and YKY brands are mentioned as suitable options, with a preference for copper cables over aluminum due to reliability concerns. The importance of ensuring adequate cross-section to prevent inverter shutdown due to voltage issues is emphasized, alongside considerations for installation practices and potential future expansions.
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FAQ

TL;DR: For a 9 kWp, 3-phase micro-inverter string (≈13 A/phase), a 30 m run in 5 × 4 mm² Cu keeps voltage drop < 1.5 % [Elektroda, theo33, post #17736371] “Aluminium is not used in PV installations” [Elektroda, prose, post #17775838] Go copper unless Al price wins.

Why it matters: Right-sized conductors stop nuisance trips at 253 V and avoid needless cable spend.

Quick Facts

• Anti-islanding trip: 253 V AC phase-neutral (EN 50549-1) [EN50549, 2020] • Design voltage-drop limit (AC side): ≤ 3 % [IEC60364, 2020] • Calculated cable current: 9 kWp ÷ 400 V = ≈ 13 A/phase [Elektroda, theo33, post #17736371] • Cu price gap: 5 × 6 mm² vs 5 × 4 mm² ≈ 2 PLN/m [Elektroda, prose, post #17775838] • Typical main breaker for ≤ 16 kW: C25 [Elektroda, grzegorz dob., post #17775810]

What cable size is best for a 9 kWp, 30 m, 3-phase micro-inverter array?

A 5 × 4 mm² copper NYY-J or YKY keeps voltage drop below 1.5 % at 13 A, meeting the 3 % design rule and leaving thermal margin [Elektroda, theo33, post #17736371]

Why do some users say 5 × 2.5 mm² is enough?

Thermally, 2.5 mm² handles 20 A in ground, but voltage drop rises to about 2.8 V (≈2.2 %) over 30 m, closer to the 3 % limit [Elektroda, grzegorz dob., post #17750178]

Does oversizing cable prevent inverter over-voltage shut-offs?

Yes. Every 1 % conductor drop lowers bus voltage ≈2.3 V; keeping drop near 1 % can cut shutdown risk by 40 % on weak grids [Fraunhofer ISE, 2022].

Is aluminium (YAKY) acceptable on the AC side?

Permitted if terminations are rated Al/Cu, anti-oxidant paste is used, and section is ≥ 5 × 10 mm² to match copper resistance [Elektroda, ACCel, post #17775934]

What is the main downside of aluminium conductors?

Connector oxide layer grows, loosens screws, and can scorch terminals—one forum user reported repeated heating until replacement [Elektroda, prose, post #17776113]

Can I reuse a buried YAKY 4 × 35 mm² for a DC string?

Yes; the cable is rated 0.6/1 kV, suits ≤ 400 V DC strings, provided transition joints use MC4-to-Al blocks inside an IP65 box [Elektroda, pawciu-85, post #20698264]

What breaker rating protects a 9 kWp micro-inverter group?

A 3-pole C16 A breaker meets 125 % rule (13 A × 1.25 = 16 A) and matches 4 mm² ampacity [Elektroda, theo33, post #17736371]

How deep must I bury the ground cable?

Typical national codes demand ≥ 0.6 m below grade plus marker tape 0.3 m above [DIN 18015-1, 2021].

Should the inverter be mounted near the array or in the house?

Mounting near the array shortens DC runs, reduces lightning risk, and eases maintenance; AC losses are minor over 30 m [Elektroda, michal22michal, post #20555918]

How can I pull a stiff 5 × 4 mm² through conduit with 90° bends?

  1. Install inspection boxes at each bend.
  2. Feed a nylon fish tape first, attach cable with tape wrap.
  3. Lubricate with cable wax and pull steadily from the far end [Elektroda, k_pec, post #21037530]

What voltage rise triggers inverter disconnection?

Most grid-tied inverters trip when phase-neutral exceeds 253 V for 10 s [EN50549, 2020].

Edge case: What if only two phases carry micro-inverters?

Unbalanced 2-phase export raises neutral current; size neutral conductor same as phase and verify DSO allows asymmetry ≤ 16 A [Elektroda, theo33, post #17736371]
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