What type of device must be capable of separating PV system DC circuits from other circuits?

A barrier or partition is essential in ensuring that the photovoltaic (PV) system's direct current (DC) circuits can be effectively separated from other circuits. This separation is crucial for safety and compliance with the National Electrical Code (NEC), as it helps prevent electrical hazards such as shock or fire that could arise from unintended connections or interactions between different circuits.

The barrier or partition serves as a physical divide, ensuring that maintenance can be performed safely on the PV system without impacting other electrical systems. Such devices are often necessary in electrical installations to maintain clearances and provide protection against accidental contact, which further enhances safety in the installation environment.

In contrast, the other options do not fulfill this specific requirement. A non-listed switch may not be approved for use in isolating circuits according to code. A cable connector primarily serves to join cables and does not offer the necessary separation. A fuse holder is intended for the management and protection of circuits, but it does not provide the required physical separation needed for safety standards in PV installations. Hence, the use of a barrier or partition is the most effective and compliant method for achieving the separation of PV system DC circuits from other circuits.