Grounding requirements for DC battery cabinets

Does a DC system need grounding?

A DC system often does not require grounding because, unlike AC, it maintains a constant polarity (positive and negative). This eliminates the need for a reference ground point to complete the circuit. This is because the negative terminal effectively acts as the ground within the system.

What are the disadvantages of grounding a DC system?

One major drawback of grounding DC systems is ground loop interference. Most industrial devices (such as DC circuit breakers, VFDs, PLCs, etc.) are properly grounded to provide a return path for fault current and ensure safety. However, if the Negative (-Ve) terminal of the DC system is also grounded, it creates two connections to the earth.

Do I need a grounding system?

NEC 2023, Article 250.162 requires a grounding system for two-wire and three-wire DC systems supplying a premises when the operating voltage is greater than 60V DC and less than 300V DC (*see exceptions in 250.162 (A)). In high-voltage DC (HVDC) transmission systems, a grounding system is essential, similar to grounding and earthing in AC systems.

What voltages need to be grounded?

In contrast, AC voltages such as 120V, 230V, and 240V, which have a high potential for electric shock, must be properly earthed and grounded according to IEC and NEC codes (Article 250). Grounding is mandatory for higher DC voltages, industrial applications, and hybrid AC/DC systems.