In a one-family dwelling, an ESS shall not exceed ___ volts DC between conductors or to ground.

• A. 60 volts
• B. 100 volts
• C. 120 volts
• D. 240 volts

Answer: (B)

The question tests how the safety threshold for DC energy storage systems (ESS) in a dwelling is defined. When an ESS is kept at or below 100 volts DC between any two conductors or to ground, it is treated as a lower-risk, “low-voltage” installation, which carries fewer and simpler safety and wiring requirements. Staying under this limit helps reduce shock and arc hazards in a home environment and aligns with the code’s category for such systems.

If the ESS voltage were higher than 100 V DC, more stringent protections would come into play—stronger disconnects, more robust enclosures, stricter wiring methods, and additional labeling and protective measures to address the greater hazard. That’s why the limit is set at 100 volts, making 100 volts DC the best choice.