Quick Answer
NEC sections 705.12 and 705.12(A) address the requirements for disconnecting means and overcurrent protection devices for photovoltaic (PV) systems, including DC breakers for solar arrays.
DC Breaker Sizing
According to NEC 705.12(A), the overcurrent device for a PV system should be rated to protect against the maximum current output of the DC source, including any inverters, charge controllers, or other DC sources. To determine the required DC breaker size, you’ll need to calculate the short-circuit current (Isc) of the solar array using the following equation: Isc = (VA rating of the array) / (PV system voltage). For example, if the solar array has a VA rating of 10,000 and the system voltage is 480V, the short-circuit current would be 20.8 amps.
Selecting the Correct DC Breaker Type
When selecting a DC breaker, it’s essential to consider the type of circuit and the level of fault protection required. For PV systems, a Type 1 DC breaker is typically used, which can interrupt the fault current without causing damage to the inverter or other system components. Type 1 DC breakers are designed to interrupt currents up to 200 amps. In contrast, Type 2 DC breakers are used for smaller systems and can interrupt currents up to 100 amps.
Installation Requirements
When installing DC breakers in a PV system, it’s crucial to follow the manufacturer’s instructions and local electrical codes. According to NEC 705.12, the DC breaker should be installed as close as possible to the point where the PV system is connected to the inverter or other DC source. Additionally, the DC breaker should be accessible for maintenance and testing. This typically means installing the DC breaker in a readily accessible location, such as a breaker panel or a dedicated enclosure.
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