§712 — Solar Power Systems (PV)

Section 712 of NEN 1010 (NEN-EN-IEC 60364-7-712) contains the additional requirements for the electrical installation of solar power systems — the panels (modules), string wiring, inverter, and connection to the house installation. The general standards remain fully applicable; §712 describes what is different because the source is unique: a PV string delivers voltage as soon as light falls on it — switching off the grid does not de-energize the panel.

Architecture

PV modules → string → DC isolator → inverter → AC isolator → distribution board
   (DC side)                                  (AC side)

Two galvanically separated sides:

DC side (panels → inverter input): sunlight = voltage, can rise to 1000 V DC for string inverters. Not disconnectable from the grid.
AC side (inverter output → distribution board): standard 230/400 V AC, switches together with the main switch.

DC side — requirements

DC isolator (§712.536.2.2)

A switchable DC isolator must be installed between the PV string and the inverter.

Purpose: allows the technician to work safely on the inverter without covering the panels. The DC isolator is located as close as possible to the inverter (usually directly next to it in the same enclosure or as a separate DC switch). Requirement: rated for the string's open-circuit voltage (Voc at STC × 1.15 for low temperature) and short-circuit current (Isc × 1.25).

Typical value: Voc-string 600 – 800 V DC; select a 1000 V DC switch with a current rating ≥ Isc × 1.25 (≈ 15 A for modern 10 A modules).

String fuses (§712.434.1)

A DC fuse is required per parallel string only if the number of parallel strings > 2 (rule of thumb ÷ 3) and if the Isc backfeed to a single string exceeds the fuse rating of the module cable. For 1- or 2-string inverters: no string fuse required.

Type: gPV (DC-rated, fast characteristic), standardized in IEC 60269-6. Placement: preferably in a "string combiner box" on the roof or in the attic, close to the string connection. Voltage class ≥ 1000 V DC.

Cable — DC side (§712.522)

Type PV cable (H1Z2Z2-K), UV-resistant, ozone-resistant, double insulation, tested up to 1500 V DC.
Minimum cross-section 2.5 mm² (Cu). For long runs (>20 m), use 4 mm² to achieve a voltage drop ≤ 1 % — otherwise, the system loses efficiency.
Do not bundle + and − cables in a common conduit → reduces loop area and thus overvoltage induction during lightning strikes.
Conductor color: red (+) and black (−) — not a legal requirement but best practice for maintenance.

Earthing of panels (§712.411)

The metal frame of each panel and the support structure must be treated as an "extraneous conductive part" and connected to the house's earthing rail — typically using a 6 mm² Cu wire (yellow/green) running down along the support structure to the earthing rail.

Purpose: in the event of a lightning strike or static charge, this earthing lowers the potential to a safe level. NEN-EN 62561-1/3 explicitly addresses the lightning protection system for PV — for houses with a roof length ≤ 10 m, no lightning protection installation is required, but earthing of metal parts is mandatory.

AC side — requirements

Own final circuit (§712.531)

A PV inverter supplies power to its own, separate circuit in the distribution board — not a shared lighting circuit. MCB selection: based on the continuous output current of the inverter (P/U), plus margin for PV peak (inverters sometimes deliver 5–10 % above nominal in cool/sunny weather).

Example: 5 kW inverter (single-phase) → 5000 / 230 = 21.7 A. Choose B25 or C25. For 3-phase 10 kW: 10 000 / (1.732 × 400) = 14.4 A → B16 or C16.

Residual current protection (§712.411.3.2)

For PV installations with transformerless inverters (modern, standard since 2015), a type-B RCD 30 mA (or integrated DC detection in the inverter) is mandatory. Transformerless inverters have no galvanic isolation between DC and AC — an insulation fault on the DC side injects a DC component into the AC leakage current, which a type-A RCD does not detect.

Practical: most inverters (SolarEdge, Enphase, GoodWe, SMA) have integrated DC leakage current detection (≥ 6 mA DC + 60 mA AC) that complies with VDE 0126-1-1 / IEC 62109-2. In this case, an external type-A RCD 30 mA on the AC side suffices — significantly cheaper. Check the inverter datasheet for the label "RCMU integrated" (Residual Current Monitoring Unit).

Disconnect relay (§712.551 / NEN-EN 50549)

The inverter must disconnect within 0.2 s in the event of a grid failure, undervoltage, or overvoltage.

Requirement from the grid operator: no export without grid, to prevent islanding (a technician working on an apparently dead grid would otherwise be hit by PV power via feed-in). Functionally part of every modern inverter; supports anti-islanding tests in conformity with EN 50549-1 (LV, ≤ 16 A) or -2 (MV, > 16 A).

Grid connection

≤ 17 A single-phase: single-phase connection via standard distribution board.
> 17 A or systems > 5 kW: 3-phase connection mandatory by the grid operator, otherwise imbalance occurs (one phase exports, two remain consuming).
Net metering scheme: still in force in 2026 in NL but being phased out; above-statutory relevance for design (battery storage becomes commercially more viable).

Smart meter

For installations > 800 W: register with Energieleveranciers.nl; the grid operator activates feed-in on the smart meter. Without this step, the meter registers export as import (consumer pays for their own generation).

Lightning protection (§712.443)

Type-2 SPD (8/20 µs, 20 kA) on the AC side, in the distribution board.
Type-2 DC-SPD at string inverters, in or near the DC isolator.
For DC cable lengths > 10 m running along the outside of the roof: consider a type-1 SPD (direct lightning strike nearby).
Connection of the support structure to the lightning protection system (LPS) only if an LPS is present — otherwise not, as it draws a lightning strike into the PV system.

Inspection (§712 in NEN 1010 §6)

Standard according to NEN-EN-IEC 62446-1:

Visual — modules, cables, IP-rating of connectors (MC4), DC isolator.
String open-circuit voltage Voc — compare with datasheet × temperature correction. Deviation > 5 % → mismatch / defective panel.
String short-circuit current Isc — measure with PV tester under comparable irradiance.
DC insulation resistance — string-to-earth, 1000 V DC test, ≥ 1 MΩ.
Earth continuity — frame + support structure ≤ 0,3 Ω to MET.
Functional test AC side — RCD trip, anti-islanding (short the grid with test device: inverter must stop within 0.2 s).
Loop impedance Zs — measured from the PV final circuit.
DC polarity — before switching on the inverter: + on + and − on −. Reversal destroys the inverter input.

Report in IEC 62446-1 format (PV-specific certificate); copy to the owner. Periodic re-inspection within NEN 3140 cycle (1 × per 4–5 years for fixed installation).

Common mistakes

Type-AC or type-A RCD on transformerless inverter without RCMU — no DC detection, DC side insulation fault is not tripped.
String cable via PVC insulation outside the roof — must be H1Z2Z2-K with UV stabilization; PVC cracks after 2 years of sun exposure.
MC4 connectors from different brands — not always tolerance-compatible, contact resistance increases, hot-spot risk on the roof.
PV final circuit shared with household load — feed-in to consumption on the same circuit can cause uncontrollable behavior; and when the MCB trips, both consumption and export are lost.
No DC isolator — unsafe for maintenance on the inverter; panels deliver voltage as soon as there is light. Covering a panel with a cloth is not a safety measure (leaks 30 – 50 V through).
Forgetting to earth the panel frame — most common finding during inspection. No key change for commissioning.

Solar Power Systems (PV)