Quick Answer
Dedicated circuits are not strictly necessary for string inverters, but a properly sized main breaker and an isolated ground can reduce the risk of electrical shock and ensure safe operation.
Circuit Requirements
When installing string inverters, it’s essential to follow the National Electric Code (NEC) guidelines. In particular, Article 690 of the NEC addresses the requirements for inverter and combiner box installations. A main breaker or a main disconnect is necessary before the inverter, but this can be a single main breaker in a panel rated for the combined inverter and charge controller loads, or a separate main disconnect panel. For a typical residential setup, a 100-amp main breaker is a common choice.
Grounding and Bonding
A dedicated ground rod or a bonded grounding system is not strictly necessary for string inverters. However, an isolated ground or a grounding system that isolates the inverter from the main electrical panel can reduce the risk of electrical shock. This is particularly important when working with DC circuits, which can be lethal even at low voltages. For example, a 12V DC circuit can deliver a lethal shock of 2-3 amperes. A properly sized main breaker and an isolated ground can help prevent such accidents.
Installation Considerations
When installing string inverters, it’s crucial to consider the overall electrical system design. This includes selecting the right size and type of inverter, as well as ensuring that the main electrical panel can handle the combined load of the inverter and charge controller. A common rule of thumb is to size the main breaker or disconnect to handle 125% of the combined load. For example, if the inverter and charge controller combined load is 20 amps, a 25-amp main breaker or disconnect would be a suitable choice.
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