The moment right before first startup is when a rushed mistake is most expensive to discover — after the system is live, energized, and potentially feeding into a load or the grid. A short, systematic pre-commissioning pass catches the vast majority of installation errors while they're still cheap and safe to fix, instead of finding out the hard way once everything is powered up.
Mechanical checks
- All panel mounting hardware torqued to spec, no loose clamps or rails
- Racking properly grounded and bonded (see our grounding inspection guide for the full process)
- No visible physical damage to panels, frames, or enclosures from installation
- Cable runs properly secured and protected from abrasion, UV exposure, and rodent access
- Combiner boxes and enclosures sealed against water and dust ingress
Electrical checks
- String voltage (Voc) measured and matches expected value for the number of panels in series
- Polarity verified on every string before connecting to the combiner or charge controller
- No unintended short circuits or continuity between positive and negative conductors, or between conductors and ground
- All terminal connections torqued to the manufacturer's specified value — not just hand-tight
- Overcurrent protection (fuses/breakers) correctly rated for the actual circuit, not oversized "to be safe"
- Cable sizing verified against actual run length and current — use our cable calculator if you haven't already sized it
On a few installations, running through this checklist before startup caught a loose terminal connection that looked perfectly fine at a glance — it only showed up once we actually torque-checked it. Skipping that step and energizing the system first would have meant discovering it later as a hot spot or an intermittent fault, instead of a two-minute fix during commissioning.
System configuration checks
- Inverter/charge controller settings match the actual battery type and capacity (for hybrid/off-grid systems)
- Correct grid country/region code set on grid-tied inverters — an easy-to-miss setting that will simply prevent startup if wrong
- Charge controller sized correctly for the array — check with our charge controller calculator
- System labeling and signage in place (disconnect locations, warning labels) where required by local code
First-startup sequence
- Verify all disconnects are in the correct position and no one is working on the system before energizing anything
- Bring up DC side first (panels to combiner/charge controller), confirm expected voltage readings
- Bring up the inverter/charge controller, watching for any immediate fault codes on startup
- Bring up the AC side or load connections last, confirming correct voltage and, where applicable, correct phase
- Monitor the system for the first 15-30 minutes of operation rather than walking away immediately — most startup issues show up quickly
Frequently asked questions
Is a pre-commissioning checklist different from a maintenance checklist?
Yes — pre-commissioning is a one-time verification before a system is first energized, focused on catching installation errors. Maintenance checks happen periodically afterward and focus on wear, corrosion, and performance degradation over time.
Do small residential systems really need this level of checking?
The scale changes, but the risk doesn't disappear — a small system with a wiring error can still cause a fire or shock hazard. The checklist scales down in time required, not in importance.
What's the most commonly skipped item on this list?
Torque-checking terminal connections is probably the most frequently skipped step, since a connection can look fine visually while still being under-torqued — and it's one of the more common causes of early-life failures and hot spots.