How to Choose the Right Breaker Size for Off-Grid Systems?

Calculating Breaker Size

To determine the correct breaker size, start by calculating the total continuous amperage of the connected loads. You can find this information on the nameplate of the equipment, such as a refrigerator or air conditioner. For example, a 5.5 kW air conditioner typically draws 46 amps. Consider the total continuous amperage of all connected loads and round up to the nearest 10 amps to ensure the breaker can handle the maximum anticipated load. Additionally, consider the surge or inrush current of the loads, which can be up to 3-5 times the continuous rating. Use the maximum surge current to determine the breaker size, and select a breaker that can handle the surge without tripping.

NEC Code Requirements

The National Electric Code (NEC) requires that breakers be sized according to the load requirements of the equipment. For example, the NEC requires a 30-ampere breaker for a 15-kW load. However, in off-grid systems, it’s common to use larger breakers to account for the higher surge currents and potential voltage spikes. To comply with the NEC, use a breaker that is sized according to the maximum continuous load, but also consider the requirements for grounding and bonding. Make sure the grounding system is adequate to protect against electrical shock and ensure the breaker is properly installed and labeled according to the NEC code.

Subpanel Breaker Selection

When selecting breakers for a subpanel, consider the total amperage of the connected loads and the maximum surge current. Select a breaker that can handle the maximum anticipated load without overloading or causing a fire hazard. It’s also essential to ensure the subpanel is sized according to the load requirements and that the grounding system is adequate to protect against electrical shock. Use a 100-ampere or larger subpanel for larger systems and consider using a main breaker or main disconnect to provide a clear path for the electrical power.