Changes to DC Grounding Conductor Sizing in ABYC A-31 (2025)
The previous 2020 edition of ABYC A-31 required the DC grounding conductor for chargers, inverters, and inverter/chargers to have an ampacity equal to that of the DC positive conductor. A limited exception allowed the grounding conductor to be one size smaller under specific overcurrent protection conditions.
The 2025 edition replaced this method with a new sizing approach based on the rating of the DC overcurrent protection device. ABYC also introduced TABLE 1 specifically for DC grounding conductor sizing. The DC grounding conductor must have a minimum size as specified in TABLE 1, based on the size of the DC overcurrent protection device for the battery chargers, inverters, and inverter/chargers.
TABLE 1 – DC Grounding Conductor (Case Grounding) Sizing
NOTE: Conductor size based on insulation temperature rating of 105° C or higher.
This revision eliminates the previous “same size as DC positive conductor” rule and aligns grounding conductor sizing more closely with modern fault current protection practices and other industry standards. The result is a reduction in the oversizing of DC grounding conductors in large systems. This is possible because the grounding conductor carries short circuit fault current only briefly, often for just a fraction of a second, until the overcurrent protection device opens the circuit.
It is worth reminding that the DC grounding conductor is connected from the metal case or chassis and is not required if the case is made of plastic or other nonconductive material and the case completely isolates the DC conductors from any grounded internal metal parts, and there are no grounded metal parts the ungrounded DC terminal could contact.
For more details, refer to the 2025 ABYC A-31, Battery Chargers and Inverters, or contact the ABYC Standards and Compliance Department at [email protected].