Construction term · Glossary
GFCI (Ground-Fault Circuit Interrupter)
Verified vs OSHA sources · 2026-10-05
A protective device that constantly compares the current flowing out to and back from a tool; if it detects even a small imbalance (current leaking to ground — like through a worker's body), it cuts the power in milliseconds. On construction sites, OSHA requires GFCI protection on 120-volt, 15- and 20-amp temporary receptacles to prevent electrocution.
Also known as: ground fault circuit interrupter, ground-fault interrupter
On this page
GFCI (Ground-Fault Circuit Interrupter) at a glance
- Detects current leaking to ground and trips within milliseconds.
- Required on 120V, 15/20-amp temporary receptacles on construction sites.
- One of the two accepted ground-fault protection options (the other is an AEGCP).
- Protects PEOPLE from shock — different from a circuit breaker, which protects wiring.
In plain English
The device that shuts power off the instant electricity starts leaking to ground — for example, through a person. It reacts in a fraction of a second, fast enough to stop a shock from becoming a fatal electrocution. It's the reason job-site power outlets have that “test/reset” button.
What the rule says
“All 120-volt, single-phase, 15- and 20-ampere receptacle outlets on construction sites, which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection.”
In context
A concept governed primarily by OSHA's construction standards, 29 CFR Part 1926 — the rules that apply on jobsites rather than the general-industry 1910 set.
Where this is written in OSHA's rules
- 29 CFR 1926.404(b)(1)Read on eCFR / OSHA.gov
- 29 CFR 1926.404(b)(1)(ii)Read on eCFR / OSHA.gov
Example
A worker using a drill on a damp slab nicks the cord; current begins leaking through the tool toward ground. The GFCI on the temporary receptacle senses the tiny imbalance and cuts power in a fraction of a second — stopping what could have been a fatal shock.
Why it matters
A GFCI is the single most effective device for preventing electrocution from portable tools and cords — the exact hazards common on wet, rough construction sites. Because electrocution is a “Fatal Four” cause of death, missing or bypassed GFCIs on temporary power are a serious, frequently cited electrical violation.
GFCI vs. circuit breaker
A GFCI protects PEOPLE — it trips on a small ground-fault current (as little as ~5 mA) that could injure a person. A circuit breaker protects the WIRING — it trips on a large overload or short (many amps) to prevent fire. A tool can electrocute you at a current far below what trips a breaker, which is why GFCIs are required.
GFCI vs. the assured-grounding alternative
| Ground-fault protection option | How it works |
|---|---|
| GFCI (typical) | Device trips on ground-fault current; protects the person |
| Assured Equipment Grounding Program | Documented inspection/testing of cords and equipment grounding |
GFCI (Ground-Fault Circuit Interrupter): frequently asked questions
- What does a GFCI do?
- It monitors the current going to and returning from a tool and, if it detects a small imbalance (current leaking to ground, such as through a person), it shuts off power within milliseconds to prevent electrocution.
- Are GFCIs required on construction sites?
- Yes — OSHA requires GFCI protection on 120-volt, 15- and 20-amp temporary receptacles used by employees (29 CFR 1926.404(b)(1)), unless the employer instead runs an assured equipment grounding conductor program.
- What's the difference between a GFCI and a circuit breaker?
- A GFCI protects people by tripping on a tiny ground-fault current; a circuit breaker protects wiring by tripping on a large overload or short. A shock hazard can exist at currents far below what trips a breaker.
Related terms
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Governing OSHA standards
More Construction terms
The part of Title 29 of the Code of Federal Regulations that contains OSHA's General Industry standards — the default rulebook for most American workplaces (manufacturing, warehousing, healthcare, etc.) that aren't covered by the construction, maritime, or agriculture standards. It includes core rules like Hazard Communication (1910.1200) and the permissible exposure limits (1910.1000). Several 1910 standards are cross-referenced into construction via Part 1926.
29 CFR 1926The part of Title 29 of the Code of Federal Regulations that contains OSHA's Construction standards — the “Safety and Health Regulations for Construction.” It governs construction, alteration, and repair work, with construction-specific rules for fall protection (Subpart M), scaffolds (Subpart L), excavations (Subpart P), electrical (Subpart K), and more. Where a task isn't addressed in 1926, some general-industry (1910) standards apply by reference.
Anchor PointThe secure attachment point a personal fall arrest system (PFAS) ties off to — the “A” in the ABC of fall arrest. Under 29 CFR 1926.502(d)(15), a non-engineered anchorage must support at least 5,000 pounds per attached worker; alternatively, it can be an engineered anchorage designed and supervised by a qualified person with a safety factor of at least two.
Atmospheric TestingMeasuring the air in a confined space (or other hazardous atmosphere) with a calibrated direct-reading instrument before and during entry. OSHA requires testing in a set order — oxygen first, then flammable gases and vapors, then potential toxic contaminants — and defines the acceptable ranges: oxygen 19.5%–23.5%, flammables below 10% of the LEL, toxics below their exposure limits.
BenchingAn excavation cave-in protective system that cuts the sides into a series of horizontal steps (benches), usually with vertical or near-vertical faces between levels. It's one of OSHA's accepted protective systems under Subpart P — but it is NOT permitted in Type C (the least stable) soil.
Competent Person (Excavation)The competent person OSHA's excavation standard (Subpart P) requires on every trenching job — someone trained in soil classification and protective systems, who can identify cave-in and other hazards AND has authority to remove workers and correct problems. They must inspect the excavation daily before work starts, throughout the shift, and after any rain or event that could increase the hazard.
Confined SpaceA space that is large enough for a worker to bodily enter, has limited or restricted means of entry or exit, and is not designed for continuous occupancy. If it also contains — or could contain — a serious hazard (a hazardous atmosphere, engulfment material, an entrapping configuration, or any other recognized serious hazard), it becomes a permit-required confined space (PRCS).
Controlling EmployerUnder OSHA's Multi-Employer Citation Policy (CPL 02-00-124), the controlling employer is an employer with general supervisory authority over a worksite — including the power to correct safety and health violations itself or to require others to correct them. This is typically the general contractor or construction manager. A controlling employer can be cited for a hazard at the site even if none of its own employees are exposed, because it has a duty to exercise reasonable care to prevent and detect violations by the other employers on site.
Sources & verification
- 29 CFR 1926.404(b)(1) (eCFR / OSHA.gov)
- 29 CFR 1926.404(b)(1)(ii) (eCFR / OSHA.gov)
- OSHA — Ground-Fault Circuit Interrupters (GFCIs)
- 29 CFR 1926.404 — Wiring design and protection (eCFR)
Reviewed by HazComFast against eCFR, OSHA.gov, NIOSH, and the Federal Register. Last reviewed 2026-10-05. This glossary is general information, not legal advice; OSHA State-Plan states (e.g. California, Michigan) may adopt stricter requirements.
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