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

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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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#31 21035505 06 Apr 2024 23:21

hindoos hindoos

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Post #31
21035505 06 Apr 2024 23:21

Well, there will be some 90-degree bends, see the illustrative drawing below
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#32 21037530 08 Apr 2024 13:34

k_pec k_pec

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Post #32
21037530 08 Apr 2024 13:34

hindoos wrote:
o there will be some 90-degree bends, see the illustrative drawing below

In this configuration, the routes are only inspections at the bends of the sewage system (pipes) in order to be able to do anything with this piping in the future. Of course, they are designed so that the cabling can be pushed through them.

An alternative - in a conduit or some piping on the ground and together with it on the wall. Or strips or channels. You can do it differently - whatever is most convenient and economical.
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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?

Install inspection boxes at each bend.
Feed a nylon fish tape first, attach cable with tape wrap.
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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