Essential Electrical Equipment
Solar PV installations require careful selection and coordination of protective devices to ensure safety, code compliance, and reliable operation over 25+ years.
Circuit Protection Devices
- DC Circuit Breakers: Rated for DC voltage (typically 600-1,500V). Must interrupt DC arcs without zero-crossing. Polarized breakers — observe + and - markings.
- Fuses: gPV type specifically for PV applications. Fast-acting, high breaking capacity (≥10kA). Required for each string if >2 parallel strings.
- DC Disconnects: Lockable, load-break rated. Must isolate all ungrounded conductors simultaneously. Required at point-of-entry to building.
Series vs Parallel Design
Series: Voltages add, current stays same. Higher voltage = lower current = smaller cables and lower losses. Must stay within inverter MPPT voltage range. Shading on one panel reduces entire string output.
Parallel: Currents add, voltage stays same. Better shade tolerance. Requires combiner box with string fusing. Higher current = larger cables and higher losses.
Combiner Box Components
DC disconnect, string fuses/breakers, surge protection device (SPD Type 2), and optionally a DC monitoring module (current sensors per string). NEMA 4X/IP65 enclosure for outdoor installation.