Safety Switches & Disconnects

When photovoltaic panels convert the sun’s energy into electricity, the power generated is direct current (DC). Typically, the systems are designed with DC system voltages in the 400-600V range. This is much higher than typically found in building systems. The higher voltage when combined with the lack of a current sine wave with zero crossings, creates a number of challenges in wiring, particularly when switching circuits on and off.

DC circuits consist of two conductors – a positive and a negative. In most PV systems, one of these conductors is grounded (like a neutral in an AC system). Which of the two conductors is grounded is specified by the solar panel manufacturer. The more common application is a negative ground, and the location of this bond is usually found at the inverter. Per CEC 14-100 only the current carrying ungrounded conductor shall be switched. Thus, in a negative-grounded system, only the positive conductor is switched.

Unlike AC systems that possess a current sine wave with zero crossings, the interruption of higher voltage DC circuits requires an increased air gap to safely and quickly interrupt and break the arc. The increased gap is accomplished by wiring multiple poles of a single switch in series for safe arc interruption. The Eaton offering is an “out of the box solution” , compliant with Section 50-012 CEC Part 1, CSA / ESA approved, suitable for switching one positive circuit, complete with negative ground conductor and compliant with Photo Voltaic application warning labels.

The fusible switch design provides enhanced safety, as the fuse is completely de-energized on both the line and load side when the switch is in the OFF position. As well, the Eaton PV switch requires only one fuse per switch – saving the customer at least one fuse on each switch.