A direct current (DC) power combiner operable to interconnect multiple interconnected photovoltaic strings is disclosed. The DC power combiner may include a device adapted for disconnecting at least one photovoltaic string from the multiple interconnected photovoltaic strings, each photovoltaic string connectible by a first and second DC power line. The device may include a differential current sensor adapted to measure differential current by comparing respective currents in the first and second DC power lines. A first switch is connected in series with the first DC power line. A control module is operatively attached to the differential current sensor and the first switch. The control module may be operable to open the first switch when the differential current sensor measures the differential current to be greater than a maximum allowed current differential, thereby disconnecting the photovoltaic string from the interconnected photovoltaic strings.