Incident energy is the heat energy a worker could receive at a given working distance from an arc flash, and it decides what level of PPE the worker must wear and how far the arc flash boundary sits. The clearing time of the upstream protective device is a key factor; clearing in the instantaneous range can keep incident energy below 8 cal/cm2 for many industrial conditions. Under NFPA 70E the arc flash boundary is the distance where incident energy falls to 1.2 cal/cm2, so higher incident energy pushes the boundary farther out. For DC equipment such as PV inverters and combiners, calculation methods have little test backing; EPRI field tests found that measured incident energy rose linearly with PV array size. In battery storage, a DC arc flash study found worst-case incident energy of 22.746 cal/cm2 at 18 inches on an unfused stack, which corresponds to PPE category 4. The equipment label shows the available incident energy or the PPE category, and the analysis must be reviewed at least every 5 years or whenever the system changes.
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related_toc1 drafted · lead AC arc flash
Incident energy calculations for AC arc flash are well established and backed by industry tests.
sec=h12 h=6e12ea069aeesec=h18 h=ddfdc2bab6b6sec=h5 h=086b216ff4ecc2 drafted · lead DC arc flash
For DC systems such as PV and battery storage, incident energy calculation methods are not backed by standardized methods or broad testing.
sec=h12 h=6e12ea069aeesec=h18 h=ddfdc2bab6b6sec=h28 h=826e6b628063sec=4.4 h=2ab51dd1ee3fc3 drafted · lead IEEE 1584 proposed
IEEE 1584 provides the main industry equations for AC incident energy and arc flash boundary calculations.
sec=h18 h=ddfdc2bab6b6sec=h5 h=086b216ff4ectbl=12.r3 h=1e0de072cfdbsec=4.7 h=06bbb568a238c4 verified · fact Arc-rated clothing
Arc-rated clothing is selected according to the incident energy at the task working distance.
sec=h58 h=883631174febsec=h84 h=62413b97e6dctbl=15.r1 h=019ca35cfa11verified by: review-workflowverified on: 2026-10-24
c5 drafted · lead Personal protective equipment proposed
sec=h18 h=ddfdc2bab6b6sec=4.4 h=2ab51dd1ee3fc6 drafted · lead Arc flash hazard assessment proposed
sec=h58 h=883631174febsec=4.7 h=06bbb568a238sec=4.9 h=f5108ad95cd4c7 verified · fact Arc flash labeling proposed
Labels carry available incident energy with working distance, or the PPE category, plus the arc flash boundary.
sec=h58 h=883631174febsec=4.4 h=2ab51dd1ee3fverified by: review-workflowverified on: 2026-10-24
c8 drafted · lead Overcurrent protection
The protective device clearing time at the arcing current largely determines incident energy.
sec=h5 h=086b216ff4ecsec=h58 h=883631174febc9 verified · fact Powin Stack750 / Centipede proposed
A DC arc flash study calculated worst-case incident energy for this battery system.
sec=4.4 h=2ab51dd1ee3fverified by: review-workflowverified on: 2026-10-24
related_to c4