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How this is calculated#

AS/NZS 5139 asks for a battery system to be classed before it is installed: which hazards its chemistry carries, which voltage class it is in, and how much energy an arc at its terminals would release. This tool works all three from a few inputs and reads the tables that follow from them.

The hazards and the fire hazard level come from the chemistry. Lithium ion is fire hazard level 1, lead acid and nickel alkaline level 2. A note to the table lifts the level for pre-assembled lithium equipment that meets the industry Best Practice Guide, and for lead acid or nickel alkaline in cases rated V0. The decisive voltage class comes from the battery's highest d.c. voltage.

The arc flash energy uses the standard's equation. It multiplies the battery voltage, the arcing current, the arcing time divided by the working distance squared, and a factor for where the arc is: at least 3 in an enclosure and 1.5 in a room. The arcing current is half the bolted fault current. The working distance is 45 cm at most. The arcing time is 2 s where the protective device's time is not known, or where the work is on its battery side. The boundary is the distance where the energy falls to 1.2 cal/cm². The appendix tables are this equation at 45 cm and a factor of 3, and a test runs every printed row through it.

The energy then sets the PPE level, the consequence level for the risk assessment, and, in a home or outside one, the limits on where the system may go.

Worked examples#

• A 48 V lithium home battery with 6 kA at its terminals releases 4.27 cal/cm² over 2 s, PPE Level 2. Above 4 cal/cm² in a home it needs a dedicated room or fire hazard level 1.
• The same battery with inter-string fuses clearing in 0.1 s releases 0.21 cal/cm², PPE Level 1.
• A 24 V lead acid bank in a battery room away from the house releases 2.13 cal/cm² at a factor of 1.5, PPE Level 1.
• A 204.8 V pre-assembled lithium home battery with 9 kA is DVC-C and releases 27.31 cal/cm², PPE Level 4.
• A 350 V system with 15 kA in a plant room releases 77.78 cal/cm², so it fails: no PPE level applies above 40.

Limits#

The tool works the energy at one point with one arcing time. It does not find the bolted fault current, which comes from the battery maker or the home battery tool, or a fuse's clearing time at that current, which comes from its curve. It does not grade the likelihood side of the risk matrix.

The tool reads the 2019 edition as published. Amendment 1 (2025) is not on hand, so check any change it makes before relying on a figure.

See also: Home battery, Arc flash and Battery.