Quick Answer
For off-grid systems, it's recommended to use 100-200 amp main breakers in the electrical panel and size subpanel breakers accordingly, considering total circuit loads and NEC code requirements.
Choosing the Right Main Breaker
When selecting a main breaker for your off-grid electrical panel, it’s essential to consider the total electrical load of your system, including generators, solar panels, and any battery banks or inverters. A general rule of thumb is to size the main breaker at 80-100% of the total load, leaving some headroom for future upgrades or additional components. For example, if your system has a total load of 20 kilowatts (kW), a 200-amp main breaker is a suitable choice.
Subpanel Breaker Sizing
Once you’ve determined the main breaker size, you can calculate the number and size of breakers needed for your subpanel. NEC code requires that subpanel breakers be sized based on the total circuit load, with a minimum of 15-20 amps per circuit. For example, if your subpanel has 6 circuits, you would need at least 6 x 20 amps = 120 amps of breaker capacity. In this case, you might use a 100-amp main breaker and 20-amp breakers for each subpanel circuit.
Grounding and NEC Code Basics
When wiring your off-grid electrical panel, it’s crucial to follow NEC code guidelines for grounding and bonding. This includes connecting the neutral bus bar to the grounding bus bar, using a grounding rod or plate, and ensuring all equipment and wiring is properly grounded. The NEC requires that the grounding system be rated for the maximum fault current of the system, which is typically 200 amps or less for residential off-grid systems. Consult a licensed electrician or the NEC codebook for specific requirements and guidelines on grounding and bonding in off-grid electrical systems.
Find more answers
Browse the full Q&A library by topic, or jump back to the topic this question belongs to.