110.15 High-leg marking
On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded, one phase conductor has a higher voltage to ground than the other two. That conductor is commonly called the high leg. It must be permanently identified by an orange outer finish, by orange marking, or by another effective means. The identification must be visible at each splice and termination where the grounded conductor is also present.
Why the high leg has to be obvious
A high-leg delta system can supply multiple voltages, but the high leg is not suitable for every line-to-neutral load. Clear identification helps prevent incorrect connections and equipment damage. Higher phase-to-ground voltage means identify it before someone connects the wrong load.
110.16 Arc-flash hazard marking
Other than dwelling units, certain equipment likely to require examination, adjustment, servicing or maintenance while energized must have permanent arc-flash marking. Examples include service equipment, switchboards and switchgear, enclosed panelboards, industrial control panels, meter socket enclosures and motor control centers. The marking must be clearly visible to qualified persons before they begin work.
What the label has to say
Nominal system voltage. Arc-flash boundary. Available incident energy and working distance, or the minimum required PPE level. The date the assessment was completed. The label tells the worker what hazard exists before the enclosure is opened.
Do
Identify high-leg conductors clearly and consistently. Verify arc-flash labels are present where required. Coordinate labeling with the latest system study. Update labels when system changes affect the hazard.
Do not
Do not assume conductor color alone is obvious in existing work. Do not treat arc-flash labels as generic warning stickers. Do not leave outdated study information on modified equipment. Do not wait until commissioning to resolve labeling requirements.
Field tip
When modifying an existing electrical system, ask three questions. Did the available fault current change? Did protective-device settings change? Did the arc-flash study change? If yes, the existing label may no longer represent the actual hazard. Related: available fault current and SCCR.
The takeaway
110.15 identifies the high leg. 110.16 communicates the arc-flash hazard before energized work. Next: #024 — NEC 110.17–110.25 Servicing, Markings and Disconnects.
Code basis
NEC 2026 Article 110.15 and 110.16 education from the owner-provided Daily Code Talk. Confirm the locally adopted NEC edition and the equipment markings. Not an arc-flash study and not a substitute for an incident-energy analysis by a qualified person.