Quick Answer
NEC code requires solar system disconnects to be accessible and have a rating of not less than 100% of the short-circuit current of the system.
NEC Requirements for Solar Disconnects
The National Electric Code (NEC) outlines specific requirements for solar system disconnects in Article 705. These requirements include accessibility, labeling, and size. To ensure compliance, the disconnect must be rated for at least 100% of the short-circuit current of the solar system, which is typically determined by the maximum current output of the solar array.
Disconnect Sizing and Rating
To determine the correct disconnect size, it’s essential to calculate the short-circuit current of the system. This can be done using the formula: Isc = (Vcc x 1.25) / X, where Vcc is the DC voltage of the system, and X is the DC resistance of the cable. The resulting value should then be multiplied by 1.25 to account for system losses. The resulting current rating should match the disconnect’s ampacity.
Installing and Labeling the Disconnect
The solar disconnect must be installed in a location that is easily accessible, such as the inverter enclosure or a separate enclosure near the inverter. The disconnect must be clearly labeled as a “DC Disconnect” and must indicate the maximum current rating of the system. The label should also include the nameplate information of the solar array and any other critical system components.
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