Select the correct DC isolator rating for your solar PV system based on panel specifications and environmental conditions.
Enter your system parameters and click "Calculate Rating" to see detailed calculation breakdown.
To size a DC disconnect, calculate the maximum system voltage by multiplying panel Voc by the number of panels in series and applying a temperature correction for the lowest expected temperature. The maximum current is Isc × parallel strings × 1.25 safety factor (per NEC). Select a disconnect rated for at least these calculated values.
A DC disconnect (isolator) is designed to safely isolate a circuit for maintenance but cannot interrupt fault currents. A DC circuit breaker provides overcurrent and short-circuit protection, automatically interrupting fault currents. Solar PV systems typically use both: the breaker for protection and the disconnect for safe manual isolation during servicing.
Solar panel Voc increases as temperature drops below the 25°C standard test condition. In cold climates, the combined string voltage can significantly exceed the sum of nameplate Voc values. If this exceeds the disconnect's voltage rating, it can cause insulation breakdown, arcing, or fire. Always calculate voltage at the lowest expected ambient temperature.