Ten critical mistakes in photovoltaic installation (+ solutions)

4. Underestimating the importance of wiring and electrical protection

Safety and performance: suitable cabling is essential

Wiring accounts for 8 to 12% of the total cost but determines 100% of safety. Wiring errors are responsible for 65% of electrical incidents on PV installations.

Common errors:

• Insufficient cable cross-section: overheating, line losses (up to 5% of output)
• Non-compliant cables: use of standard domestic cables instead of UV-resistant PV cables
• Lack of DC protection: no disconnect switch, fuses or surge arresters on the DC side
• Loose MC4 connectors: contact resistance, risk of electric arcing

Calculate the required cable cross-section accurately

Cable sizing cannot be improvised: an undersized cable causes ongoing financial losses for 25 years, whilst an oversized cable represents an unnecessary extra cost. The voltage drop must never exceed 3% between the panels and the inverter.

Our free calculator takes all the essential parameters into account:

• Exact distance between panels and inverter
• Operating voltage of your system (12V, 24V, 48V, high voltage)
• Maximum current and power output
• Type of current (DC for panel-to-inverter, AC for inverter-to-grid)
• Ambient temperature and correction factor

“Professional cabling with appropriate cable sizes and compliant protection guarantees safety for 25 years. It’s an investment of €200–€300 that protects a €10,000 system. Use our free calculator to avoid any sizing errors.” — Wattuneed Design Office

Photovoltaic cables: mandatory specifications

Warning: H07V-K or U-1000 R2V domestic cables are NOT suitable for a photovoltaic installation. You must use specific PV cables (EN 50618 standard or equivalent) that offer:

• UV and weather resistance (outdoor lifespan of 25+ years)
• Operating temperature -40°C to +90°C (up to +120°C peak)
• Double reinforced insulation
• Resistance to ozone and chemicals
• Low smoke emission in the event of a fire

Essential electrical protection

All installations must include:

• DC (direct current) side: isolator switch, overcurrent protection, Type II surge arrester
• AC (alternating current) side: 30mA Type A residual current circuit breaker, decoupling protection
• Earthing: < 30 Ω mandatory, equipotential bonding

Refer to the detailed Wattuneed wiring diagrams for an installation compliant with standards NF C 15-100 and IEC 62548.