BESS and rooftop solar.
Two additions to the campus, two 2027 articles written for them. The PV array is the one source on the property that cannot be switched off; the BESS is the battery room's arithmetic wearing a container. Neither forgives habits learned on utility-fed gear.
There is no lockout for the sun
Article 380 is built on one sentence of physics: qualified-person training for PV must include recognising the continuously energized nature of the panels. Illuminated modules are energized modules; Article 120's disconnect-and-verify sequence has nothing to grip on the array side. From that follow the article's hard rules — only qualified persons work on PV installations under 380.4, and a risk assessment precedes any work on an energized array under 380.5.
The thresholds are 310.2's set — 1000 W contact thermal, 100 V dc with 40 mA for shock, 150 V dc with 1.2 cal/cm² for arc flash — and a string of series modules walks over the shock and arc flash lines by design. The array's combiner boxes and inverters are expressly pointed to the other Chapter 3 articles: the dc side to 310, the conversion electronics to 330, any storage to 360 or 370.
The connector rules are the article's teeth
380.6 is written at the level of the physical act because the physical act is where PV hurts people. Before manipulating conductors on an energized system, the risk assessment must establish the maximum open-circuit voltage and the maximum current to be interrupted. Plugging and unplugging connectors requires procedures that prevent creating a short, and — the operative habit — verification of no load current before disconnecting. An MC4 parted under load draws a dc arc that does not self-extinguish at a zero crossing, because there isn't one. The current check before the pull is the whole game.
Roof work compounds it: the arc flash boundary and approach boundaries operate in three dimensions on a surface with fall protection, ballast trays, and no aisles. The permit's restrict-unqualified-persons element has real work to do on a roof shared with HVAC trades.
The BESS is Article 360 at container scale
Inside the enclosure, the BESS answers to the battery room's rules: the 360.3(A) thresholds, the arc flash risk assessment at 150 V and above, sectionalizing in place of the impossible lockout, and the ÷4 short-circuit power arithmetic at fault currents that dwarf a UPS string. Where the design uses supercapacitors for ride-through, Article 370 adds its own regime — theoretical maximum power at V²/4R, and the residual-charge rules for cells that can rebuild voltage after discharge. The fire-side requirements of NFPA 855 run alongside all of this as siting and suppression law; 70E owns the worker-facing electrical decisions inside the box.
A rooftop string 'isolated' at the inverter disconnect and treated as dead at the combiner — 400-plus volts of open-circuit potential still on every homerun, because the disconnect isolated the inverter, not the sun. The one-line was read in the direction the power flows at noon; the hazard flows from the modules whenever there is light.
PV or BESS task? The walk's scope and source questions handle the array's always-on nature explicitly — run it before the roof hatch opens.
This is the material of the 8- and 16-hour NFPA 70E classes — taught on the 2027 edition, against data center topology, about 55 times a year. Private onsite days run against your one-lines.