Direct-current (DC) systems are becoming increasingly common; one major reason is the growth in solar applications. Part VIII of Art. 250 provides requirements specific to DC systems, but it’s important to note that all of Art. 250 applies to DC systems except sections that are specifically intended for AC systems [250.160].
To avoid Code violations when grounding and bonding DC systems, go to the start of Art. 250 and refer to Figure 250.1. Use this as your guide to applying Art. 250 generally, while also making sure to refer to Part VIII. (Chapters 1 through 4 apply, also).
A DC system can be a 2-wire or 3-wire system. If it’s a 3-wire system, the neutral must be grounded [250.162(B)].
If it’s a 2-wire system, it must be grounded if it supplies premises wiring and is operating at more than 60V but less than 300V. However, there are three exceptions to this rule. One of those exceptions: The system has a ground detector and supplies only industrial equipment in limited areas (where installed adjacent to or integral with the supply source).
