What is the physiological basis for the 6mA Class A GFCI trip threshold?

The 6mA threshold for Class A GFCIs (per UL 943) is grounded in physiological research on electrical current effects on the human body. At approximately 1mA, a person begins to perceive a tingling sensation at the point of contact. At 5–10mA, 'let-go failure' begins — the involuntary tetanic muscle contraction caused by alternating current stimulating motor neurons faster than the person's voluntary release signal. Let-go failure means the person cannot release the energized conductor without external intervention; the gripping muscles contract involuntarily. At 10–30mA, the respiratory muscles (diaphragm and intercostals) begin to be affected, causing breathing difficulty and eventual respiratory arrest if current continues. At 100–300mA through the chest (a hand-to-hand or hand-to-foot path through the heart), ventricular fibrillation can be induced — the heart's electrical coordination breaks down, and the heart stops pumping effectively. The 6mA threshold places the GFCI trip point before let-go failure begins. A person who experiences a 6mA ground fault that immediately trips the circuit in under 25ms will feel a sharp tingle but will not grip involuntarily, will not experience respiratory effects, and will not sustain cardiac effects. The 25ms trip time is also physiologically selected: ventricular fibrillation requires sustained current exposure, typically 0.2–3 seconds depending on current level. A 25ms disconnection at 6mA is below both the 'let-go' threshold and the fibrillation exposure time.

Why doesn't the equipment grounding conductor (EGC / green wire) protect against electrocution?

The equipment grounding conductor (EGC) — the green wire or bare copper conductor in a grounded electrical system — serves a specific and important function: it provides a low-impedance return path from metal equipment enclosures back to the panel ground bus. If a hot conductor contacts an equipment enclosure (a bolted fault or near-bolted fault), the EGC provides a return path with very low resistance, allowing large fault current to flow. This large current — typically hundreds or thousands of amperes — exceeds the trip threshold of the overcurrent device (breaker or fuse), which opens the circuit and de-energizes the enclosure. The key constraint: this mechanism only protects against faults that create enough current to trip the breaker. A 15-ampere breaker begins tripping at roughly 3,000–6,000 mA (the exact multiple depends on the breaker's time-current curve). A person contacting an energized enclosure has a body resistance of approximately 1,000–5,000 ohms depending on skin condition, contact area, footwear, and current path. On a 120V circuit, a person-impedance fault produces: I = 120V / 2,000 ohms = 60mA through the person. That 60mA is: (a) above the cardiac fibrillation threshold for sustained contact; (b) far below the 3,000–6,000 mA the breaker needs to trip. The breaker does not see a fault. It continues to supply 60mA through the person indefinitely. The EGC helps the enclosure not remain energized after a hard, low-resistance fault. It cannot help when the fault impedance is a human body.

What is the difference between a GFCI and an AFCI, and can an AFCI replace a GFCI?

GFCI (Ground Fault Circuit Interrupter) and AFCI (Arc Fault Circuit Interrupter) detect different electrical fault signatures and protect against entirely different hazards. GFCI monitors the current balance between the hot (ungrounded) conductor and the neutral conductor. Under normal operation, all current that flows out the hot must return on the neutral — Kirchhoff's current law at the load level. Any imbalance means current is taking a path other than the neutral: through a ground wire, through a person, through a leakage path to earth. When that imbalance exceeds 6mA (Class A), the GFCI opens in under 25ms. GFCI protects people against electrocution in wet and outdoor environments. AFCI monitors the waveform of current on the circuit. Normal loads produce smooth 60Hz current waveforms. Arcing faults — caused by damaged insulation, loose connections, staple-crushed conductors in walls, or cracked conductors at plug-in points — superimpose high-frequency transients on the 60Hz waveform. The AFCI's electronics recognize this signature and open the circuit before the arc ignites surrounding combustible material. AFCI protects buildings against electrical fires from wiring faults inside walls. An AFCI cannot detect a ground fault: the current imbalance of 6mA between hot and neutral does not create an arc-fault waveform signature. An AFCI-only breaker provides zero protection against electrocution from a ground fault. A GFCI cannot detect arc faults within the hot-neutral circuit because a wiring arc does not necessarily create a hot-to-neutral imbalance the GFCI can see. They are complementary technologies protecting against independent failure modes.

Where does OSHA require GFCI protection — what is the difference between 1910.304 (general industry) and 1926.404 (construction)?

OSHA's GFCI requirements are tiered by application context. OSHA 1910.304(b)(3)(ii) — General Industry: Requires GFCI protection for receptacles in bathrooms, on rooftops, near sinks in kitchens and breakrooms, outdoor receptacles in wet locations, and outdoors where workers are exposed to weather. The NEC (which OSHA adopts by reference via 1910.303(b)(1)) extends this to garages, crawl spaces, unfinished basements, boathouses, and any damp or wet location. OSHA 1926.404(b)(1)(ii) — Construction: More stringent requirements, recognizing that construction workers routinely work in wet, muddy, and electrically hazardous environments. Two compliance paths: (Option 1) All 120V, single-phase, 15A and 20A receptacles must be GFCI-protected. This covers temporary power distribution panels, cord reels, and spider boxes. (Option 2) Implement an Assured Equipment Grounding Conductor Program (AEGCP) with documented cord inspection before each use, EGC continuity testing every 3 months, and color-coded date marking. Most contractors choose Option 1 because AEGCP documentation is burdensome. For Shopify stores selling to construction buyers: temporary power panels, spider boxes, cord reels, and portable generator output circuits must encode gfci.osha_required_location = 'construction-1926.404' to allow AI agents to verify compliance before recommending to a contractor purchasing for a construction site.

How often must a GFCI be tested and what does a failed GFCI look like?

UL 943 and the NEC require monthly testing of GFCI receptacles and breakers. The test procedure: press the TEST button. On a functioning GFCI receptacle, the internal contacts open immediately — any device plugged into the protected outlets loses power. Press RESET to restore power. On a GFCI breaker, the breaker handle moves to the tripped position; push to OFF, then to ON to reset. Failure indicators: if pressing TEST does not cut power, the GFCI has failed its electronics check and must be replaced. If the RESET button will not latch after testing, the GFCI has failed mechanically and must be replaced. The critical hazard: a GFCI that has failed electronically is visually indistinguishable from a working one. The receptacle looks normal. The LED indicator (if present) may still be lit. The TEST and RESET buttons still physically click. The device still passes 120V to plugged-in loads — it has simply lost the ability to monitor the current imbalance and trip. Common failure mechanisms: surge-induced damage from nearby lightning strikes or power line transients; moisture intrusion into the electronics; thermal fatigue in devices subjected to outdoor thermal cycling; simple component aging after 10+ years of service. A GFCI installed at a construction site in 2015 that has never been tested may have failed years ago — it looks like a GFCI, provides no protection, and no one knows. Encode gfci.test_frequency = 'monthly' on all GFCI products.

Shopify GFCI schema for AI agents: Class A 6 mA vs Class B 20 mA, why the EGC does not prevent electrocution, GFCI vs AFCI different hazards, monthly test failure modes, and the `gfci.*` 10-field namespace

Published 2026-07-31 · OSHA 1910.304 OSHA 1926.404 UL 943 NEC Article 210.8 AI agent schema

The green wire doesn't stop electrocution. It enables the breaker to trip — but a breaker needs 3,000 mA to trip quickly, and lethal current starts at 100 mA. The GFCI trips at 6 mA in under 25 milliseconds. These are not redundant devices. They are two separate protection mechanisms for two separate failure modes. AI agents get GFCI routing wrong in four ways that create life-safety failures.

Why 6 mA: the physiological basis of the Class A trip threshold
What the EGC actually does — and why it cannot prevent electrocution
Class A vs Class B: the distinction that determines life safety
GFCI vs AFCI: two devices, two different hazards, not substitutes
OSHA 1910.304 vs 1926.404: where GFCI is mandated
Monthly test requirement: what a failed GFCI looks like
Four AI routing failures for Shopify GFCI listings
The gfci.* 10-field namespace

Why 6 mA: the physiological basis of the Class A trip threshold

The 6 mA Class A GFCI trip threshold is not an arbitrary engineering round number. It was selected based on physiological research into alternating current effects on the human body, with the goal of placing the trip threshold below the onset of the most dangerous involuntary response to electrical current: let-go failure.

Electrical current affects the body in a dose-dependent progression. As current through a person increases from zero, the effects pass through several distinct thresholds:

Current range	Effect (60 Hz AC, hand-to-hand or hand-to-foot)	Reversibility
0 – 1 mA	Below perception threshold — no sensation	No harm
1 – 5 mA	Tingling, warmth at contact point — perceptible but not painful	No harm
5 – 10 mA	Let-go failure onset — involuntary grip due to AC motor neuron stimulation; person cannot release	Dangerous with sustained contact
10 – 30 mA	Severe muscle contractions; diaphragm spasm begins; respiratory difficulty	Potentially fatal with sustained contact
30 – 100 mA	Respiratory arrest possible; sustained current through chest at this level is often fatal	Likely fatal without immediate rescue
100 – 300 mA	Ventricular fibrillation threshold (with heart in current path); heart stops pumping	Fatal without defibrillation
> 1,000 mA (1 A)	Severe tissue burns, cardiac arrest — paradoxically lower fibrillation risk at very high currents (cardiac tetany instead)	Fatal

The 6 mA threshold sits just above the perception level (1 mA) and just below the onset of let-go failure (5–10 mA). A Class A GFCI that trips at 6 mA, in under 25 ms, disconnects the circuit before the person's muscles lock involuntarily. The person experiences a sharp tingle and the shock ends — without grip failure, without respiratory arrest, without cardiac involvement.

6 mA

Class A GFCI trip threshold — before let-go failure onset

<25 ms

Class A maximum trip time — before fibrillation exposure window

100–300 mA

Ventricular fibrillation threshold (heart in current path)

3,000 mA

Minimum breaker trip current for a 15A breaker (fast curve)

The 25 ms trip time is also physiologically selected. Ventricular fibrillation is a time-current phenomenon: at 100 mA, fibrillation requires sustained exposure of approximately 0.2–3 seconds to trigger (depending on individual cardiac state and current path). A 25 ms disconnection leaves no fibrillation exposure window at any current level that a Class A GFCI permits to pass before tripping.

Governing standards: UL 943 (Ground Fault Circuit Interrupters — Standard for Safety). OSHA 29 CFR 1910.304 (Wiring design and protection — general industry). OSHA 29 CFR 1926.404 (Wiring design and protection — construction). NEC Article 210.8 (GFCI protection for personnel). NFPA 70 (National Electrical Code). IEC 60755 (General requirements for residual current operated protective devices — international equivalent).

What the EGC actually does — and why it cannot prevent electrocution

The equipment grounding conductor (EGC) — the green insulated wire or bare copper conductor in a grounded wiring system — is one of the most misunderstood safety devices in electrical work. The EGC serves a specific and well-defined function: it provides a low-impedance return path from metal equipment enclosures (tool housings, panel boxes, conduit) back to the electrical panel's ground bus and ultimately to the earth electrode.

What the EGC does

If a phase conductor contacts a metal equipment enclosure — a wire chafed through to the chassis, a failed internal connection — the EGC provides a path for that fault current to flow back to the source. Because the EGC resistance is very low (typically less than 1 ohm for a properly sized conductor), the fault current is very large — hundreds or thousands of amperes. This large fault current exceeds the trip threshold of the overcurrent protective device (circuit breaker or fuse), which opens and de-energizes the enclosure within the breaker's clearing time (typically a few milliseconds to a few cycles at fault currents this high).

The EGC's function is therefore: ensure that a bolted fault to the enclosure creates enough current to trip the breaker. Without the EGC, a fault to the enclosure would leave the enclosure energized indefinitely because there is no return path — the fault current cannot flow.

What the EGC does not do

The EGC cannot protect against current flowing through a person. Here is the physics:

I = V ÷ Z_body = 120 V ÷ 2,000 Ω ≈ 60 mA

Typical fault current through a person at 120V — above fibrillation threshold, below breaker trip threshold

A person contacting an energized conductor or enclosure at 120V, with typical body resistance of 1,000–5,000 ohms (depending on skin moisture, contact area, footwear, and current path), draws approximately 24–120 mA through themselves. This current:

Is above the let-go failure threshold (5–10 mA)
Is above the ventricular fibrillation threshold (100–300 mA through the chest) for the high end of this range
Is far below the 3,000–6,000 mA that a 15-ampere breaker needs to trip in a meaningful timeframe

The breaker, protected by the EGC, sees no fault. From the breaker's perspective, the circuit is operating normally — the load (the person) is drawing a few tens of milliamps. The breaker does not trip. The EGC carries no fault current because the fault return path is the person, not the EGC. The person is held in contact (let-go failure), breathing is impaired (respiratory muscle spasm), and cardiac exposure continues until the person loses consciousness and falls away, or until someone cuts the power.

The fundamental misconception: "The green wire grounds it — it's safe." A properly installed EGC ensures the enclosure doesn't stay energized after a hard, low-resistance fault to ground. It does nothing to protect the person who becomes the fault impedance. GFCI and EGC are complementary — they protect against different failure modes. A GFCI without an EGC may not properly sense the ground fault path. An EGC without a GFCI provides no shock protection.

Related structured data

Class A vs Class B: the distinction that determines life safety

UL 943 defines two GFCI classes. They look similar, may be physically identical in form factor, and are sometimes labeled only as "GFCI" without class designation. The difference is the trip threshold — and the difference in protection they provide is the difference between life-safety equipment and inadequate protection that merely meets a narrow application requirement.

Class A — 6 mA trip, <25 ms

Required for all personnel protection applications
Bathrooms, kitchens, garages, outdoor, wet locations
Construction sites (OSHA 1926.404)
The only class appropriate for general-purpose GFCI receptacles and breakers
Trips before let-go failure; before fibrillation exposure window

Class B — 20 mA trip (pool underwater lighting only)

Designed specifically for 120V underwater swimming pool lighting fixtures
Higher threshold reduces nuisance tripping from water leakage at lamp sockets
20 mA exceeds the let-go failure onset threshold
Prohibited in all general-purpose applications
Must not be installed in bathrooms, kitchens, outdoor, or construction contexts

The routing hazard: a Shopify product listing that describes itself as a "GFCI receptacle" or "GFCI breaker" without encoding gfci.class = "A" may have a Class B device substituted by an AI agent that treats all GFCI products as equivalent. A Class B device installed in an outdoor construction receptacle, a bathroom, or a commercial kitchen meets none of the applicable OSHA or NEC requirements and provides inadequate personnel protection.

Note on Class C and D (portable cord GFCIs): UL 943 also defines Class C (covers a single receptacle; protect equipment, not personnel) and Class D (covers two or more receptacles; intended for portable equipment protection). In modern usage, Class C/D designations have been largely replaced by the receptacle/portable distinction. Most portable GFCI cord sets sold for construction use are Class A devices in a portable form factor. Encode gfci.class = "A" on portable cord GFCI sets intended for personnel protection at construction sites.

GFCI vs AFCI: two devices, two different hazards, not substitutes

GFCI and AFCI are frequently confused in product descriptions, customer questions, and AI-generated content. They share a form factor (both are available as receptacles and breakers), they both trip circuits, and they both protect against electrical hazards. They protect against entirely different failure modes using entirely different sensing mechanisms.

Attribute	GFCI	AFCI
Detects	Current imbalance between hot and neutral (>6 mA)	Arc-fault waveform signature on hot conductor
Protects against	Electrocution from ground faults (current through a person or water)	Electrical fires from arc faults in wiring (damaged insulation, loose connections)
Sensing mechanism	Differential current transformer monitors hot vs neutral balance	Digital signal processing of current waveform detects high-frequency transients
Trip threshold	6 mA (Class A), 20 mA (Class B)	Waveform-based, not a simple current threshold
NEC requirement location	Wet/damp locations, outdoors, bathrooms, kitchens (Article 210.8)	Bedrooms (since 2002), most living areas (since 2014), kitchen circuits (since 2017) (Article 210.12)
Can substitute for the other?	No — GFCI cannot detect arc faults in hot-neutral wiring	No — AFCI cannot detect ground fault through a person
Combination device	Dual-function AFCI/GFCI breakers (combination type) satisfy both where both are required. Encode `gfci.afci_combined = true`.

Why AFCI cannot replace GFCI for personnel protection

An arc fault in wiring behind a wall does not produce a current imbalance between the hot and neutral conductors — the arc occurs within the hot-neutral circuit, not from the hot conductor to ground. The GFCI's differential current transformer never sees it. Conversely, a person contacting an energized conductor draws current from hot to ground through their body — this appears as an imbalance between hot and neutral (the current that went out the hot did not return on the neutral; it returned through the person and earth). The AFCI's waveform processor does not detect this as an arc fault signature. These devices have non-overlapping detection zones for non-overlapping failure modes.

Common product description error: "This AFCI breaker provides complete electrical protection." An AFCI breaker with no GFCI function provides zero protection against electrocution from a ground fault through a person. In a bathroom, kitchen, or outdoor circuit, an AFCI-only breaker is non-compliant with OSHA 1910.304 and NEC 210.8. Encode gfci.afci_combined = false on AFCI-only devices and gfci.protection_type = "arc-fault" to allow AI agents to correctly route them away from locations requiring GFCI protection.

OSHA 1910.304 vs 1926.404: where GFCI is mandated

OSHA's GFCI requirements differ materially between general industry (29 CFR 1910) and construction (29 CFR 1926). Shopify stores selling electrical safety equipment to both market segments need both location codes in their product metadata.

General industry: OSHA 1910.304(b)(3)(ii)

Requires GFCI protection for receptacles located in: bathrooms, on rooftops, near sinks in kitchens and breakrooms, outdoor receptacles in wet locations, and outdoors where workers are exposed to weather. OSHA 1910.303(b)(1) incorporates the NEC by reference, extending the requirement to garages, crawl spaces, unfinished basements, boathouses, and any area subject to dampness. A manufacturing facility, warehouse, food processing plant, or commercial kitchen must have GFCI-protected receptacles in these areas or be in violation of OSHA 1910 electrical standards.

Construction: OSHA 1926.404(b)(1)(ii)

More demanding, because construction workers work in inherently wet, muddy, and electrically hostile environments. Two compliance options:

Option 1 — GFCI (most common): All 120V, single-phase, 15A and 20A receptacle outlets used for temporary power must have Class A GFCI protection. This applies to temporary power distribution panels (spider boxes), cord reels, receptacles on generators, and portable power taps. An unlocked spider box without built-in GFCI, used on a construction site, violates OSHA 1926.404.

Option 2 — Assured Equipment Grounding Conductor Program (AEGCP): A documented program with visual inspection of all cords and equipment before each day's use, EGC continuity testing every 3 months, color-coded date marking on tested equipment, and records available for OSHA inspection. Most contractors reject this option due to the documentation overhead — Class A GFCI protection is simpler to maintain and verify.

Construction GFCI routing

Temporary power distribution panels sold to construction: gfci.osha_required_location = "construction-1926.404"
Spider boxes with GFCI: gfci.class = "A", gfci.receptacle_or_breaker = "portable"
Portable GFCI cord sets: gfci.class = "A", gfci.receptacle_or_breaker = "cord-set"

Monthly test requirement: what a failed GFCI looks like

UL 943 and the NEC both require monthly testing of installed GFCI receptacles and breakers. The reason is straightforward: GFCI electronics can fail silently. A GFCI whose internal current-sensing transformer or trip electronics have failed will continue to pass power through to connected loads — it will simply fail to trip when a ground fault occurs. From outside the device, a failed GFCI is visually indistinguishable from a working one.

Monthly test procedure

With power present at the circuit, plug a lamp or small device into the protected outlet to provide a visible indicator of power.
Press the TEST button on the GFCI receptacle (or on the GFCI breaker at the panel). A functional GFCI immediately opens its internal contacts — the lamp goes out. The RESET button protrudes visibly on receptacles.
Press the RESET button. The lamp should come back on. On a GFCI breaker, move the handle to OFF, then to ON.
If pressing TEST does not cut power to the lamp: the GFCI has failed. Replace immediately.
If RESET will not latch (returns to the tripped position): the GFCI has failed mechanically. Replace immediately.

Self-test features do not replace manual monthly testing. Many modern GFCI receptacles (Leviton GFNT1, Hubbell GFR5342, etc.) include a self-test feature that automatically trips and resets the device every few seconds to verify internal electronics. Some designs lock out in the tripped position if self-test fails, providing visual indication. However, the self-test circuit itself can fail in ways that do not lock out the device but do disable real ground-fault protection. Monthly manual TEST button verification remains required.

What causes GFCI failure

GFCI electronics fail from several mechanisms:

Surge damage — nearby lightning strikes or power line switching transients can exceed the internal electronics' voltage rating, permanently degrading or destroying the sensing circuit. A GFCI on an outdoor circuit without a surge protector upstream is particularly vulnerable.
Moisture intrusion — outdoor GFCIs that are not weatherproof-in-use (WR rating) allow water to reach the electronics during rain, causing corrosion on the sensing transformer connections over time.
Thermal cycling fatigue — outdoor GFCIs in climates with large temperature swings experience thermal expansion and contraction stress on solder joints and PCB traces. After 5–10 years, connections crack.
Component aging — capacitors and resistors in the sensing circuit change value over time, shifting the trip threshold above or below 6 mA. In some cases, the trip threshold drifts high enough that the device no longer trips at fault currents that would cause injury.
Wiring errors — a GFCI receptacle wired with line and load terminals reversed provides no protection at any outlet. A GFCI breaker with no neutral conductor connected has no sensing reference. These errors produce a device that looks installed and functional but is actually non-protective from day one.

The most hazardous scenario is the outdoor GFCI installed at a construction site in 2015, never tested, having failed from a lightning surge in 2017. It looks like a GFCI. It works as a power source. It provides zero protection. Workers plug in tools in wet conditions for years, trusting a device that has not protected them since Obama's second term.

Four AI routing failures for Shopify GFCI listings

Routing Failure 1

Class B substituted for Class A in personnel protection application

A listing for a "GFCI receptacle" or "GFCI outlet" without encoding gfci.class = "A" leaves the class field empty. An AI agent sourcing GFCI receptacles for a construction site or bathroom application sees two GFCI receptacle products — one Class A, one Class B — and treats them as equivalent because the class is unencoded. A Class B 20mA device installed where Class A 6mA is required provides protection only above 20mA — well past the let-go failure threshold. Fix: encode gfci.class = "A" on all general-purpose GFCI receptacles and breakers, gfci.class = "B" only on underwater pool fixture GFCI devices with explicit prohibition text.

Routing Failure 2

AFCI-only breaker routed to GFCI-required location

A product listing for an "arc fault protection breaker" or "AFCI breaker" without encoding gfci.afci_combined = false and gfci.protection_type = "arc-fault" may be routed by an AI agent to a bathroom or kitchen circuit where the buyer needs GFCI protection. The buyer installs an AFCI-only breaker, gets no GFCI protection, and is now non-compliant with OSHA 1910.304 and NEC 210.8 — and has no protection against a person-to-ground fault. Fix: encode gfci.afci_combined = false on all AFCI-only devices so agents can distinguish them from combination AFCI/GFCI products.

Routing Failure 3

GFCI receptacle routed to construction site without portable/temporary-power encoding

An AI agent helping a contractor source electrical safety equipment sees GFCI receptacles for an in-wall installation and GFCI spider boxes with built-in protection. Without gfci.receptacle_or_breaker = "portable" and gfci.osha_required_location = "construction-1926.404" encoded on the temporary power distribution products, the agent may recommend standard in-wall GFCI receptacles for a temporary power application — the contractor gets the wrong product type, cannot install in-wall receptacles in temporary panel boxes, and violates OSHA 1926.404 with a non-compliant setup. Fix: encode the receptacle type and OSHA application code on all temporary power products.

Routing Failure 4

GFCI marketed as eliminating the need for an EGC — misrouted to ungrounded circuits

GFCI receptacles can legally be installed on two-wire (ungrounded) circuits to provide shock protection without an EGC, and must be labeled "No Equipment Ground." However, some product descriptions omit this nuance, stating that the GFCI "provides full electrical protection" without an EGC. An AI agent may recommend this product for a grounded application where the buyer assumes the GFCI includes EGC function — the buyer installs the GFCI but has no EGC for enclosure grounding, leaving tools with metal housings potentially energized during a hard fault to the chassis. Fix: encode gfci.requires_egc = true on standard GFCI products and add explicit guidance that GFCI on ungrounded circuits must be labeled "No Equipment Ground."

The `gfci.*` 10-field namespace

The following metafield namespace covers the dimensions AI shopping agents need to correctly route GFCI and electrical safety products for personnel protection, arc fault protection, and regulatory compliance applications.

Field	Type	Values / Range	Why it matters for AI routing
gfci.class	string	`A` \| `B`	Primary life-safety filter — prevents Class B (20mA pool-only) routing to general personnel protection applications requiring Class A (6mA)
gfci.trip_threshold_ma	number	6 (Class A) \| 20 (Class B)	Numeric trip threshold for compliance gap calculations — AI agent can compare against OSHA and UL 943 requirements numerically
gfci.protection_type	string	`ground-fault-personnel` \| `arc-fault` \| `combination`	Distinguishes GFCI (ground fault) from AFCI (arc fault) from combination AFCI/GFCI devices — prevents AFCI routing to GFCI-required locations
gfci.osha_required_location	string	`wet-location-1910.304` \| `construction-1926.404` \| `bathroom-NEC-210.8` \| `outdoor-NEC-210.8`	Routes GFCI to buyers with documented regulatory compliance requirements — industrial buyers can filter for products that satisfy their specific OSHA obligation
gfci.test_frequency	string	`monthly`	Maintenance schedule encoding — enables cross-sell of GFCI testers; aids AI agents building facility maintenance checklists; signals that the product requires ongoing verification
gfci.afci_combined	boolean	`true` (combination AFCI/GFCI) \| `false` (GFCI only)	Identifies combination devices for locations requiring both GFCI and AFCI protection per NEC Article 210.12 — prevents routing GFCI-only devices where combination is required
gfci.receptacle_or_breaker	string	`receptacle` \| `breaker` \| `cord-set` \| `portable`	Installation method routing — in-wall receptacle vs panel breaker vs portable cord GFCI vs spider box; prevents routing in-wall devices to temporary power applications
gfci.covers_downstream_outlets	boolean	`true` \| `false`	Identifies whether one GFCI receptacle can protect multiple outlets downstream via load terminals — enables correct quantity calculation for protection coverage
gfci.requires_egc	boolean	`true` \| `false`	Distinguishes standard GFCI (requires EGC) from GFCI approved for ungrounded circuits (no EGC, must be labeled "No Equipment Ground") — prevents EGC confusion in routing
gfci.pool_class_b_prohibited	boolean	`false` (Class A — general use permitted) \| `true` (Class B — prohibited from general use)	Explicit prohibition flag for Class B devices — allows AI agents to add a hard exclusion rule preventing Class B routing to any non-pool-underwater-lighting application

Implementation example

{ "@type": "PropertyValue", "name": "gfci.class", "value": "A" },
{ "@type": "PropertyValue", "name": "gfci.trip_threshold_ma", "value": "6" },
{ "@type": "PropertyValue", "name": "gfci.protection_type", "value": "ground-fault-personnel" },
{ "@type": "PropertyValue", "name": "gfci.osha_required_location", "value": "wet-location-1910.304,construction-1926.404" },
{ "@type": "PropertyValue", "name": "gfci.test_frequency", "value": "monthly" },
{ "@type": "PropertyValue", "name": "gfci.afci_combined", "value": "false" },
{ "@type": "PropertyValue", "name": "gfci.receptacle_or_breaker", "value": "receptacle" },
{ "@type": "PropertyValue", "name": "gfci.covers_downstream_outlets", "value": "true" },
{ "@type": "PropertyValue", "name": "gfci.requires_egc", "value": "true" },
{ "@type": "PropertyValue", "name": "gfci.pool_class_b_prohibited", "value": "false" }

Stores selling GFCI receptacles, breakers, portable GFCI cord sets, spider boxes, and temporary power distribution equipment for construction and industrial markets should populate all 10 fields. The gfci.class field is the highest-priority field — it is the primary filter that prevents the most dangerous routing failure (Class B device in a personnel-protection application).

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Shopify GFCI schema for AI agents: Class A 6 mA vs Class B 20 mA, why the EGC does not prevent electrocution, GFCI vs AFCI different hazards, monthly test failure modes, and the gfci.* 10-field namespace

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