A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Unlike a fuse, which must be replaced after a single use, a circuit breaker can be reset — either manually or automatically — to resume normal operation.
How Circuit Breakers Work
Circuit breakers operate on a simple but critical principle: when electrical current flowing through a circuit exceeds a safe level, the breaker "trips" — opening the circuit and stopping the flow of electricity. This prevents wires from overheating, which could cause fires, equipment damage, or electrocution.
Inside a circuit breaker, there are two main tripping mechanisms. The first is a bimetallic strip that bends when heated by excess current, eventually triggering the trip mechanism. This handles overloads — situations where too many devices are drawing power at once. The second is an electromagnetic mechanism that responds almost instantly to the massive surge of current caused by a short circuit.
Types of Circuit Breakers
Standard Circuit Breakers are the most common type found in residential and light commercial electrical panels. They come in single-pole (120V) and double-pole (240V) configurations and are rated from 15 to 200 amps for residential use.
Arc Fault Circuit Interrupters (AFCIs) detect dangerous electrical arcs — sparks that can occur within wiring and ignite fires. The National Electrical Code (NEC) requires AFCI breakers in most living areas of new residential construction. They are available from all major manufacturers including Square D, Siemens, Eaton, and GE.
Ground Fault Circuit Interrupters (GFCIs) protect against electric shock by detecting current leaking to ground. They are required in bathrooms, kitchens, garages, and outdoor areas. GFCI breakers protect an entire circuit, as opposed to GFCI outlets which only protect the outlet and downstream devices.
Molded Case Circuit Breakers (MCCBs) are used in commercial and industrial applications. They handle higher current ratings — typically from 15A to 2,500A — and provide more precise protection settings. Common MCCB brands include Square D PowerPact, Siemens SENTRON, Eaton Series C, and GE TJD/TED.
Air Circuit Breakers (ACBs) are the largest type, used in main distribution panels and industrial facilities. They can handle currents from 800A to 6,300A and above. Major brands include ABB SACE Emax, Siemens 3WL, Schneider Electric MasterPact, and Eaton Magnum.
Major Circuit Breaker Brands
Square D (now owned by Schneider Electric) is one of the most widely used brands in the United States. Their product lines include QO (residential), Homeline (value residential), I-Line (commercial), and PowerPact (industrial).
Siemens offers the QP and QT series for residential use, the BQ series for commercial applications, and the SENTRON series for industrial use. Siemens also owns the legacy ITE brand.
Eaton (which acquired Cutler-Hammer) produces the BR and CH series for residential and light commercial use, and the Series C and HMCP lines for industrial applications.
General Electric (GE) makes the THQL and THQB series for residential use and the TED, TJD, and TJK series for commercial and industrial applications.
ABB is a major player in industrial circuit breakers, producing the SACE Tmax and Emax lines for medium and large commercial and industrial applications.
When to Replace Circuit Breakers
Circuit breakers have a long service life — typically 25 to 40 years — but they do wear out. Signs that a breaker may need replacement include: frequent tripping under normal loads, a breaker that won't stay reset, visible signs of burning or melting, a breaker that feels hot to the touch, or a breaker that is more than 30 years old.
Certain older breaker brands have known safety issues and should be replaced regardless of age. Federal Pacific Electric (FPE) Stab-Lok breakers, Zinsco/GTE-Sylvania breakers, and Pushmatic breakers have documented failure rates and are considered fire hazards by many electrical inspectors and insurance companies.
Selling Surplus Circuit Breakers
If you have surplus, used, or new circuit breakers you no longer need, they have real resale value. Industrial and commercial breakers especially — Square D PowerPact, Siemens SENTRON, Eaton Series C, GE TJD — can be worth hundreds or even thousands of dollars each depending on the model and amperage rating.
Electrical Breaker Buyers purchases circuit breakers of all types and brands nationwide. We pay fair market prices and provide free pickup for large lots. Call us at 951-733-6603 for a free quote.