CSLB C-46 Solar ContractorSafetyHard
A solar technician is working on a ground-mounted PV array where multiple parallel strings are connected to a combiner box. To safely de-energize the system for maintenance, the technician must follow a specific sequence. Which step is crucial immediately after opening the DC disconnects at the inverter but before working on the combiner box?
- ADisconnect the AC output of the inverter from the grid.
- BVerify zero voltage at the combiner box terminals.
- CMeasure the AC voltage at the utility service entrance.
- DCover the PV modules with opaque material to prevent further current generation.
Show answer & explanationAnswer & explanation
Correct answer: B. Verify zero voltage at the combiner box terminals.
After opening the DC disconnects at the inverter, the PV modules can still generate voltage and current. Before working on the combiner box, it is critical to verify zero voltage at its terminals to ensure the circuit is truly de-energized and safe to work on. This step confirms the effectiveness of the disconnects and identifies any residual charge or unexpected energy sources.
Why the other options are wrong
- A. Disconnecting the AC output is usually done before or concurrently with DC disconnects, not immediately after DC disconnects and before working on the combiner box itself.
- C. Measuring AC voltage at the utility entrance is part of overall system verification but not the immediate step after DC disconnects before working on the DC combiner box.
- D. Covering modules helps prevent generation but is typically done earlier or in conjunction with disconnects, and does not replace the critical step of verifying zero voltage.
PV System De-energization: Zero Voltage Verification
After opening disconnects in a PV system, it is crucial to verify zero voltage at the point of work before touching any conductors or components.
- PV modules can generate voltage even when disconnected from the inverter.
- Zero voltage verification confirms the absence of hazardous electrical energy.
- Use a properly rated and tested voltage meter.
- This step is essential to prevent electrical shock.
Memory trick: Disconnect, Verify, Ground, Work safely all around!