1926.404(f)(1): Electrical Systems That Must Be Grounded
Employers must ground the systems that supply premises wiring as this paragraph lists, including 3-wire DC systems, certain 2-wire DC systems over 50 volts through 300 volts, certain AC circuits under 50 volts, and AC systems of 50 to 1000 volts under listed conditions, unless an exception applies.
Key takeaways
- 1926.404(f)(1) is part of OSHA's construction standards (29 CFR Part 1926, Subpart K).
- OSHA cited it 2 times in the last 3 years, in 2 inspections, with $15,527 in current penalties.
- 1 death is linked to inspections that cited this rule.
- Related part: 1926.404(f) Grounding (241 citations).
- Free 5-minute toolbox talk for your crew below.
In this article
What this rule covers
29 CFR 1926.404(f)(1) ("Systems to be grounded") is one requirement inside 1926.404 Wiring design and protection, an OSHA construction standard (Part 1926, Subpart K). It includes 13 sub-paragraphs. The official text below is copied word for word from the Electronic Code of Federal Regulations (eCFR). The numbers, injury cases and training on this page show how OSHA enforces it on real job sites.
Official text
(1) Systems to be grounded. The following systems which supply premises wiring shall be grounded: 2 citations
(i) Three-wire DC systems. All 3-wire DC systems shall have their neutral conductor grounded.
(ii) Two-wire DC systems. Two-wire DC systems operating at over 50 volts through 300 volts between conductors shall be grounded unless they are rectifier-derived from an AC system complying with paragraphs (f)(1)(iii), (f)(1)(iv), and (f)(1)(v) of this section.
(iii) AC circuits, less than 50 volts. AC circuits of less than 50 volts shall be grounded if they are installed as overhead conductors outside of buildings or if they are supplied by transformers and the transformer primary supply system is ungrounded or exceeds 150 volts to ground.
(iv) AC systems, 50 volts to 1000 volts. AC systems of 50 volts to 1000 volts shall be grounded under any of the following conditions, unless exempted by paragraph (f)(1)(v) of this section: Open (f)(1)(iv) 2 citations
(A) If the system can be so grounded that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts;
(B) If the system is nominally rated 480Y/277 volt, 3-phase, 4-wire in which the neutral is used as a circuit conductor;
(C) If the system is nominally rated 240/120 volt, 3-phase, 4-wire in which the midpoint of one phase is used as a circuit conductor; or
(D) If a service conductor is uninsulated.
(v) Exceptions. AC systems of 50 volts to 1000 volts are not required to be grounded if the system is separately derived and is supplied by a transformer that has a primary voltage rating less than 1000 volts, provided all of the following conditions are met:
(A) The system is used exclusively for control circuits,
(B) The conditions of maintenance and supervision assure that only qualified persons will service the installation,
(C) Continuity of control power is required, and
(D) Ground detectors are installed on the control system.
Source: eCFR, text current as of 2026-10-15. Read all of 1926.404.
Injuries linked to this rule
1 death is linked to inspections where OSHA cited 1926.404(f)(1).
At 1:40 p.m. on June 6, 2024, Employee #1, employed by a company installing a temporary cooling chiller system, was working on electrical connections. The employee was running 50-foot cables (4-AWG) from the rooftop to connect to the electrical panel and the chiller's disconnect on…
Where and how often it was cited
Free toolbox talk
A 5-minute crew talk on 1926.404(f)(1), plus alerts when this rule changes. Free.
OSHA interpretation letters
None exist. OSHA has not published a letter of interpretation for 1926.404(f)(1).
Related parts of this rule
- 1926.404(f) Grounding 241 citations
- 1926.404(f)(6) Grounding path 234 citations
- 1926.404(f)(7) Supports, enclosures, and equipment to be grounded 4 citations
- 1926.404(f)(7)(iv) Equipment connected by cord and plug 3 citations
- 1926.404(f)(1)(iv) AC systems, 50 volts to 1000 volts 2 citations
- 1926.404(f)(7)(i) Supports and enclosures for conductors
- 1926.404(f)(3)(i) Portable generators
- 1926.404(f)(3) Portable and vehicle-mounted generators
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Frequently asked questions
Must 3-wire DC systems be grounded?
Yes. All 3-wire DC systems shall have their neutral conductor grounded.
When must AC circuits under 50 volts be grounded?
If installed as overhead conductors outside of buildings, or if supplied by transformers whose primary supply system is ungrounded or exceeds 150 volts to ground.
Are there exceptions for AC systems of 50 to 1000 volts?
Yes. Certain separately derived systems used exclusively for control circuits are not required to be grounded if all listed conditions are met.
About this page
Sources
- 29 CFR 1926.404 (eCFR), text current as of 2026-10-15
- U.S. Department of Labor enforcement data: OSHA inspections, citations and accident records, copied nightly; data as of 2026-10-20
3-year window. Federal OSHA only; state-plan rules are not counted. Plain-language text is a summary, not legal advice; the official text controls. Black Belt Safety is not part of OSHA or the Department of Labor.