Ground-fault detection is permitted for grounded systems, but is required for ungrounded systems [NEC Sec. 250.167(A) and (B)].
You must legibly mark your direct-current (DC) system to indicate the grounding type. The marking must be at the DC source or first disconnecting means. The marking must be of sufficient durability to withstand the environment [250.167]. These requirements and the workmanship of Sec. 110.12 exclude the use of hand-written paper signs or similarly unprofessional marking. If you don’t have a means of making a permanent placard or label, contact your electrical distributor for advice.
Are you grounding your DC system? If so, use an unspliced bonding jumper to connect the equipment grounding conductor(s) to the grounded conductor where the system is grounded (at the source or the first system disconnecting means) [250.168]. This bonding jumper must be at least as large as the system grounding electrode conductor specified in Sec. 250.166, and it must comply with Sec. 250.28(A), (B), and (C).
Is yours an ungrounded separately derived system (other than a portable one)? You still need a grounding electrode conductor connected to an electrode [250.169].
