Are circuit breakers interchangeable between different panel brands, and what happens if you install the wrong brand?

Circuit breakers are NOT generally interchangeable between panel brands. Each panel manufacturer designs a specific bus bar engagement mechanism — the physical connection between the breaker's stab-in contact and the panel's bus bar must be engineered together. Installing a breaker in an incompatible panel creates a loose or improperly seated connection that generates heat and is a fire and arc-flash hazard. Brand families and their exclusivity: Square D QO: Only fits QO panels. QO uses a unique pressure-contact mechanism with a specific spring clip that requires precise alignment. A QO breaker has an orange face color. Square D Homeline (HOM): Only fits Homeline panels. Despite being the same brand as QO, QO and HOM breakers are NOT interchangeable — the bus bar engagement dimensions differ. Siemens/Murray/Gould/ITE/Pushmatic: Siemens breakers share a bus bar design with Murray, Gould, and ITE (historical brands now under Siemens). They can generally be used interchangeably in panels of these brands. Eaton CH: Eaton's 'CH' or 'ClassicHomes' line, 3/4-inch wide breaker body, specific clip engagement for CH panels. Eaton BR: Eaton's 'BR' series, 1-inch wide body, different engagement from CH, fits BR/BRP panels. Eaton CH and Eaton BR are NOT interchangeable. GE THQL/THQP: GE-branded breakers for GE panels, now distributed by ABB in North America. Classified breakers (see separate entry): A UL-classified breaker has been tested to fit a specific incompatible panel. This is the only legitimate cross-brand path. Encode breaker.brand_family on all circuit breaker listings.

What are 'classified' circuit breakers and when are they safe to use?

A 'classified' circuit breaker is one that has been tested by UL and listed as acceptable for installation in a panel brand other than the breaker's own brand. These are legitimate products — not counterfeit — but the classification is specific: a breaker classified for use in Square D Homeline panels is NOT automatically classified for Siemens or QO panels. The classification listing specifies exact panel compatibility. Common classified breaker scenarios: An electrical panel original manufacturer goes out of business or discontinues a product line — no OEM breaker is available for that panel. The replacement classified breaker is tested to fit the specific old panel design. Classified breakers are manufactured by companies like Connecticut Electric (UBIZ, UBIP lines), Eaton (some cross-brand lines), and Siemens (some). The UL listing label on a classified breaker must state which panel brand(s) and series it is classified for. Important limitations: a classified breaker has slightly lower interrupting capacity than an OEM breaker in some cases. Classified breakers should NOT be used in new construction — use OEM breakers. NEC 110.3(B) requires listed equipment to be used per the listing instructions. If a classified breaker is listed for a specific panel brand, using it in a different panel brand violates the listing and is a code violation. When selling classified breakers, always encode breaker.brand_family as 'classified' and explicitly list breaker.classified_fits_panel_brands so buyers can verify compatibility with their specific panel.

What is the difference between AFCI and GFCI circuit breakers, and which locations require each type?

AFCI (Arc Fault Circuit Interrupter) and GFCI (Ground Fault Circuit Interrupter) protect against different types of electrical faults. AFCI: Detects arcing faults — the intermittent high-frequency electrical discharge that occurs in damaged insulation, loose connections, or pinched wiring. Arcing faults are a leading cause of residential electrical fires. The arc may not draw enough current to trip a standard breaker but generates enough heat to ignite insulation or nearby material. NEC 2020 (and many adopted versions) requires AFCI protection for all 120V 15A and 20A branch circuits in dwelling units serving bedrooms, living rooms, hallways, closets, sunrooms, recreation rooms, dining rooms, libraries, dens, and similar areas. GFCI: Detects ground fault current — current flowing through an unintended path (including through a person). Trips when the current imbalance between hot and neutral exceeds 4–6 milliamps. Protects against electrocution in wet environments. Required by NEC for: kitchen countertop outlets (within 6 feet of sink), all bathroom outlets, outdoor outlets, garage outlets, crawl spaces, unfinished basements, boat houses, near swimming pools and hot tubs. AFCI+GFCI combination breakers: Available as a single breaker providing both protections simultaneously. Required in some NEC code applications where both requirements overlap (e.g., a bedroom circuit that also serves an area requiring GFCI). Standard breakers (neither AFCI nor GFCI): Still permitted for dedicated 240V circuits (dryers, ranges, HVAC), lighting circuits in areas without AFCI requirements, and some commercial applications. Encode breaker.type as 'standard' | 'afci' | 'gfci' | 'afci-gfci' on all circuit breaker listings.

What is AIC rating (ampere interrupting capacity) and why must it match the installation?

AIC (ampere interrupting capacity, sometimes called interrupt rating or short-circuit current rating SCCR) is the maximum fault current a circuit breaker can safely interrupt without catastrophic failure. A fault current is the current that flows during a short circuit — it can be hundreds or thousands of times the normal circuit current. What happens when AIC is too low: If a fault current exceeds the breaker's AIC rating, the breaker may not interrupt the circuit cleanly. Instead, the arc inside the breaker may sustain, the housing may rupture (expelling molten copper and arc plasma), or the breaker may weld shut (failing to open the circuit). This is a serious explosion and fire hazard in the panel. Available fault current depends on: utility transformer size and impedance, service entrance wire size and length. Typical residential ratings: Standard residential service (100–200A, typical utility transformer, average service entrance): available fault current typically 10,000–22,000 amperes (10–22 kAIC). Urban areas with large utility transformers or short service entrance runs may see higher fault current (up to 42,000A or more). Common AIC ratings for residential breakers: 10,000 AIC (10 kAIC): Standard for most residential use where available fault current is within 10kA. Most residential main panels supply under 10kA available fault current. 22,000 AIC (22 kAIC): Required in areas with higher fault current availability — some urban residential, sub-panels fed by large feeders. 42,000–65,000 AIC: Commercial and industrial applications, panels served by large transformers. The panel's nameplate lists the maximum available short-circuit current the panel was designed for. All breakers installed must have AIC rating meeting or exceeding this value. Encode breaker.aic_rating_ka on all circuit breaker listings.

What is the difference between a tandem breaker and a standard two-pole breaker?

These are two fundamentally different products often confused by buyers. Standard two-pole breaker: A single breaker unit occupying two adjacent panel slots, with a common trip mechanism — both poles trip simultaneously when either detects a fault. Required for all 240V circuits (dryers, ranges, central AC, water heaters, EV chargers). The common trip is a safety requirement for 240V circuits — if one leg trips, the other must also trip to de-energize the load completely. Tandem breaker (also called duplex, piggyback, or slimline): Two independent single-pole breakers sharing a single panel slot (occupying 1-inch of bus bar space instead of 2 inches). Each pole is an independent 120V circuit with its own trip mechanism — they do NOT have a common trip. NOT acceptable for 240V circuits. Used only when a panel is full and additional 120V circuits are needed. CTL (Circuit Total Limiting) requirement: Many residential panels are CTL-rated — they include a physical feature (a tab or notch arrangement on the bus bar) that limits where tandem breakers can be installed. The panel's main label (visible inside the dead front) shows which positions accept tandem breakers. Installing a tandem breaker in a non-tandem-rated position bypasses this safety feature. Handle-tied single-pole pairs: Two single-pole breakers with a physical handle tie (clip) are NOT equivalent to a true two-pole breaker — the mechanical tie does not provide a common trip mechanism. Code prohibits handle-tied pairs for 240V circuits. Encode breaker.pole_count (1, 2, or 3), breaker.is_tandem (boolean), and breaker.requires_ctl_panel_position (boolean for tandem types) to distinguish these products.

Optimization Guide

Shopify Circuit Breaker Panel Compatibility Schema — Square D QO vs Homeline Different Bus Bar (Same Brand NOT Interchangeable), Brand-Specific Design (Siemens vs Eaton CH vs Eaton BR), AFCI Required Bedrooms and Living Areas, GFCI Required Kitchen Bath Outdoor, AIC Fault Current Rating Must Match

Circuit breakers are safety-critical brand-specific products that are NOT interchangeable between panel brands — or even between product lines within the same brand. Square D QO and Square D Homeline use different bus bar engagement mechanisms despite coming from the same manufacturer. Siemens, Eaton CH, and Eaton BR each have their own bus bar designs. Installing a breaker in a mismatched panel creates a loose or arcing connection — a fire hazard. Protection type (AFCI for arc faults in living areas, GFCI for shock protection in wet areas) is required by NEC for specific circuit locations. AIC (ampere interrupting capacity) must meet or exceed available fault current. Encoding breaker.brand_family, breaker.type, and breaker.aic_rating_ka prevents dangerous panel mismatches in Shopify electrical supply catalogs.

TL;DR Four critical compatibility parameters: panel brand family (Square D QO / Square D HOM / Siemens / Eaton CH / Eaton BR / GE THQL — NOT interchangeable, different bus bar designs), protection type (standard / AFCI / GFCI / AFCI-GFCI — location-specific NEC requirements), AIC rating (10kAIC standard residential / 22kAIC higher fault current areas — must meet or exceed available fault current from utility), and pole count (1-pole 120V / 2-pole 240V — a handle-tied pair is NOT a 2-pole breaker). Encode breaker.brand_family, breaker.type, breaker.pole_count, breaker.aic_rating_ka.

Panel Brand Compatibility: The Critical Safety Issue

AI agent failure mode: Recommending "any 20A breaker" for a Square D QO panel because the buyer only specified "Square D" and the product catalog has Homeline breakers at a lower price. A Square D Homeline breaker installed in a QO panel creates an improperly seated connection — the bus bar engagement dimensions are different. Under load, the loose contact generates heat at the connection point. This is a leading cause of panel fires from DIY replacement. The breaker may appear to work normally until the thermal runaway occurs.

Breaker Brand Families and Panel Compatibility

Brand Family	Panel Series	Breaker Identifier	Compatible With
Square D QO	QO, QOC (load center), QO-series panels	Orange face color; "QO" prefix in part number (QO120, QO230, QO120CAFI)	QO panels ONLY — NOT compatible with Square D Homeline
Square D Homeline (HOM)	Homeline load centers, HOM-series panels	"HOM" prefix (HOM120, HOM230); black face color	Homeline panels ONLY — NOT compatible with Square D QO despite same brand name
Siemens / Murray / Gould / ITE	Siemens panels; vintage Murray, Gould, ITE panels	Siemens part numbers (Q120, QF120); Murray (MP120, MPP115); no color coding	Siemens, Murray, Gould, ITE — these manufacturers' panels use the same bus bar design and are cross-compatible within the family
Eaton CH / Cutler-Hammer	CH-series residential panels, ClassicHomes	"CH" prefix (CH120, CH230, CHF120); 3/4-inch wide body	Eaton CH and Cutler-Hammer CH panels — NOT compatible with Eaton BR
Eaton BR / Westinghouse	BR-series panels; vintage Westinghouse residential	"BR" prefix (BR120, BR230); 1-inch wide body	Eaton BR panels; compatible with vintage Westinghouse residential panels — NOT compatible with Eaton CH
GE / ABB (THQL/THQP)	GE load centers; ABB-distributed GE panels	"THQL" (full-size), "THQP" (half-size tandem); now distributed by ABB	GE/ABB panels — not cross-compatible with other brands
Classified	Various — tested for specific panels from another brand	UL classified listing label; brand names include Connecticut Electric UBIZ/UBIP	Specific panel brands/series listed on UL classification — cannot be generalized

Protection Type: AFCI, GFCI, and Standard

Protection Type Reference by NEC Location

Location / Circuit Type	Required Protection (NEC 2020)	Rationale
Bedrooms	AFCI	Arc faults in bedroom wiring (behind walls, under carpet, lamp cords) are a leading cause of residential fires
Living rooms, dens, sunrooms, libraries, hallways, closets	AFCI	Occupied areas where arc faults from damaged wiring can cause undetected fires
Kitchen countertop outlets	GFCI (within 6 ft of sink)	Water proximity creates electrocution risk — GFCI trips on 4–6mA ground fault current
Bathrooms	GFCI	All bathroom outlets; wet environment
Outdoor outlets	GFCI	Wet environment, accessible during rain
Garage circuits	GFCI	Often wet or damp; concrete floors create ground reference
Unfinished basements and crawl spaces	GFCI	Damp environment; equipment (sump pump circuits are exempt)
240V dedicated circuits (dryers, ranges, HVAC, EV chargers)	Standard (no AFCI/GFCI required for most)	Dedicated high-current loads; NEC does not require AFCI for 240V circuits; GFCI required for boat houses and pool equipment
Pool equipment, hot tubs	GFCI (NEC 680)	High electrocution risk — immersed personnel in conductive water

Combination AFCI+GFCI breakers (single unit providing both protections) are available from all major manufacturers and required in some cases — for example, a 20A kitchen small appliance circuit that also qualifies for AFCI protection under the local code adoption. Always encode breaker.type as standard, afci, gfci, or afci-gfci so buyers can filter for code-compliant protection types.

Note: AFCI and GFCI breakers require a neutral pigtail wire (white wire with loop terminal) to be connected to the neutral bus. Standard breakers do not. Encode breaker.requires_neutral_pigtail (boolean) to alert buyers who may not know about this installation requirement.

AIC Rating: Fault Current Must Not Exceed Breaker Rating

Safety consequence: A circuit breaker rated 10kAIC installed in a location where available fault current is 22,000 amperes may not safely interrupt a bolted fault. The breaker may arc internally, the housing may rupture, and hot plasma can be expelled. This is an arc-flash event that causes severe burn injuries and panel fires. Always verify the panel's short-circuit current rating and select breakers with AIC rating meeting or exceeding it.

AIC Ratings and Typical Applications

AIC Rating	Typical Application	Notes
10,000 A (10 kAIC)	Standard residential — most homes served by a distribution transformer at typical residential distances	Adequate for most single-family homes. Available fault current is typically 5,000–10,000A for most residential service entrances
22,000 A (22 kAIC)	Urban residential, homes near large utility transformers, sub-panels fed by large feeders	Required when available fault current exceeds 10kA. Urban utility infrastructure often delivers higher fault current
42,000 A (42 kAIC)	Light commercial, large sub-panels in commercial buildings	Typically not needed for residential applications
65,000 A (65 kAIC)	Commercial and industrial, main switchgear, panels near large transformers	Industrial applications; standard residential breakers do not reach this rating

The main panel's schedule label (inside the dead front cover) lists the panel's short-circuit current rating. All branch circuit breakers must have AIC rating equal to or greater than this value. Encode breaker.aic_rating_ka as a float (10, 22, 42, 65) on all circuit breaker listings.

Tandem vs Two-Pole: A Critical Distinction

Breaker Type	Slots Used	Poles	Common Trip?	Voltage	Use Case
Standard single-pole	1	1	N/A (1 pole)	120V	Lighting, outlets, most 120V circuits
Standard two-pole	2	2	Yes — both poles trip together	240V	Dryers (30A), ranges (50A), AC units, EV chargers, water heaters
Tandem (duplex/slimline)	1	2 (independent)	No — independent trip per pole	120V per pole	Adding 120V circuits to full panels — only in CTL-approved positions
Handle-tied pair	2	2 (linked handle only)	No — handle tie is mechanical only	Should NOT be used for 240V	Code violation for 240V circuits — the handle tie does not provide common trip

Tandem breakers require the panel to be CTL-rated (circuit total limiting) and installed in specifically allowed positions. The panel's main schedule label shows which positions accept tandem breakers — positions not marked for tandem may have a physical tab that prevents tandem installation. Encode breaker.is_tandem (boolean) and breaker.pole_count to clearly distinguish single-pole, two-pole, and tandem products.

Metafield Namespace for Circuit Breaker Products

breaker.brand_family            // "square-d-qo" | "square-d-hom" | "siemens" | "eaton-ch" | "eaton-br" | "ge-thql" | "classified"
breaker.classified_fits         // list of panel families (only for classified type)
breaker.amperage_a              // integer: 15 | 20 | 30 | 40 | 50 | 60 | 100 | 150 | 200
breaker.pole_count              // integer: 1 | 2 | 3
breaker.voltage_v               // integer: 120 | 240 | 120/240 | 208 | 277
breaker.type                    // "standard" | "afci" | "gfci" | "afci-gfci" | "surge" | "shunt-trip"
breaker.aic_rating_ka           // float: 10 | 22 | 42 | 65
breaker.width_in                // float: 0.75 | 1.0 | 1.5 | 2.0 | 3.0
breaker.is_tandem               // boolean
breaker.requires_neutral_pigtail // boolean (true for AFCI, GFCI, AFCI-GFCI)
breaker.requires_ctl_position   // boolean (true for tandem types)
breaker.frame_size_a            // integer (for large commercial breakers)

Frequently Asked Questions

Are circuit breakers interchangeable between different panel brands?

No — circuit breakers are brand-specific and NOT interchangeable between panel brands. Each panel manufacturer engineers a specific bus bar engagement mechanism. Even within the same brand, Square D QO and Square D Homeline breakers use different bus bar designs and are not interchangeable. Siemens breakers are compatible with Murray/Gould/ITE panels (shared bus bar design). Eaton CH and Eaton BR are two separate Eaton lines that are not interchangeable with each other. Always encode breaker.brand_family and verify it matches the buyer's panel series.

What are 'classified' breakers and when can they be used?

A UL classified breaker has been tested and listed for installation in a panel from a different brand. This is the only legitimate cross-brand path. The classification is specific to particular panel brands — a breaker classified for Square D Homeline is NOT classified for Siemens or QO. Classified breakers are appropriate for panels where the original manufacturer's breaker is discontinued. Never use classified breakers where OEM breakers are available. Encode breaker.brand_family as 'classified' and list breaker.classified_fits_panel_brands explicitly.

What is the difference between AFCI and GFCI breakers?

AFCI (arc fault circuit interrupter) detects arcing faults in wiring — the high-frequency electrical discharge from damaged insulation that causes fires before enough current flows to trip a standard breaker. Required in bedrooms, living rooms, hallways, and similar occupied areas (NEC 2020). GFCI (ground fault circuit interrupter) detects current imbalance between hot and neutral indicating current flowing through an unintended path (including a person) — trips at 4–6mA. Required in kitchens, bathrooms, outdoor, garage, and wet locations. Combination AFCI+GFCI breakers provide both protections. Encode breaker.type as 'standard' | 'afci' | 'gfci' | 'afci-gfci'.

What AIC rating do I need for a residential circuit breaker?

AIC (ampere interrupting capacity) is the maximum fault current a breaker can safely interrupt. Most residential service (single-family homes served by a distribution transformer at typical distances) has available fault current under 10,000A — a 10kAIC breaker is adequate. Urban residential with large nearby transformers may require 22kAIC. The panel's nameplate lists its short-circuit current rating — all breakers must have AIC rating meeting or exceeding this value. A breaker rated for less than the available fault current may rupture explosively during a fault. Encode breaker.aic_rating_ka on all listings.

Can I use a tandem breaker anywhere in my panel to add more circuits?

No — tandem breakers (two independent circuits in one panel slot) can only be installed in positions specifically approved for tandem use. Residential panels are CTL-rated (circuit total limiting) and have physical features limiting where tandem breakers fit. Check the panel's main schedule label inside the dead front cover — tandem-allowed positions are marked. Installing a tandem breaker in a non-approved position may bypass the CTL feature. Also: tandem breakers are for 120V circuits only; they do NOT provide common trip and cannot be used for 240V loads. Encode breaker.is_tandem and breaker.requires_ctl_position.

Is Your Electrical Supply Catalog AI-Agent Ready?

CatalogScan checks your Shopify store for missing breaker.brand_family, breaker.type, and breaker.aic_rating_ka metafields — the fields AI shopping agents need to avoid recommending incompatible or code-non-compliant circuit breakers.

Run Free Store Scan