|Many people are confused about how to properly size circuit breakers for their solar system. Solar panels are considered what the NEC refers to as a continuous load. That is any electrical device that is expected to output or draw its maximum current for 3 or more hours uninterrupted. Solar modules fall into this category. The NEC requires the short circuit current (Isc) of the solar module or panel to be used for calculating the overcurrent protection and to multiply the Isc rating by 156%. This accounts for both the continuous load of the panel and other conditions that can increase their output, such as extremely cold temperatures and the cloud edge effect. When sizing circuit breakers for the charge controller output, multiply the maximum amperage rating of the controller by 125%. Charge controllers are capable of outputting their maximum amperage for 3 or more hours which means it is considered a continuous load. However, when using circuit breakers that are rated for continuous duty, such as the MidNite Solar MNEDC and MNEPV, you only need to multiply the Isc by 125% for the PV circuits. The charge controller circuit will not need any multiplier. Basically, a continuous duty rated circuit breaker offsets the need for a continuous load calculation. For more information about the NEC and photovoltaics, please reference the National Electric Code [NEC Article 690]. Specifics about overcurrent protection and sizing can be found in [NEC Article 690.8].|
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