Electricity: Understanding How It Works: Circuit Breakers and Fuses


Branch circuits that distribute electricity throughout your house are typically rated from 15 to 50 amps. When a circuit draws too much current, wires can overheat, insulation can degrade and fail and the risk of fire greatly increases. To prevent this, each circuit is protected at the serv ice panel by an overcurrent protective device. Most pre-1965 panels have fuses, and newer panels have circuit breakers. If a circuit draws excess current, the breaker will trip off or the metal strip inside the fuse melts open, stopping current flow.

Circuit failures are often caused by overloads, short circuits and ground faults. Overloads are caused when too many lights or appliances are on a circuit. Short circuits occur when a hot wire touches the neutral wire or another hot wire. A hot wire that touches a grounded metal box would be a ground fault. Before resetting the breaker or replacing the fuse, identify and correct the problem.

A heavily used circuit that fails when you turn on a high-wattage appliance is probably overloaded. The solution is to move portable appliances to a different circuit with unused capacity.

If the circuit still fails, check for a short circuit or ground-fault condition. Unplug lamps and appliances and look for dam aged plugs or cords. Look for discoloration and smell for burned odors at receptacles, switches and fixtures. With lamps and appliances still unplugged, reset the breaker or replace the fuse. If the circuit fails again, there may be hidden problems in the house wiring. If the circuit fails only when you turn on a lamp or appliance, the problem may be corrected by repairing the item.

Are you looking for home electrical items -- such as switches and fuse boxes -- or parts and accessories for ones you already have? Try our dedicated electrical supply pages here:






Brand Name Manufacturers


A circuit-breaker panel will usually have a double-pole main breaker and single-pole or double-pole branch breakers.


A fuse panel will usually have main pullout blocks with cartridge fuses and plug fuses for the branch circuits.

Auxiliary panels vary widely and may include lever-operated main switches with circuit breakers or cartridge or plug fuses.
Single-pole breakers protect 120-volt lighting and appliance circuits usually rated at 15 or 20 amps

Circuit Breakers

Single-pole breakers protect 120-volt lighting and appliance circuits usually rated at 15 or 20 amps.

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Recommended Reading

Safe Home Wiring Projects

Book Description:

The primary intimidating factor in working with electricity (and the thing that frightens many people away from even trying to do home wiring projects) is, obviously, the fact that it can be dangerous--even deadly--if not done properly and if appropriate safety precautions aren't taken. Rex Cauldwell has put together one of the most comprehensive, basic, step-by-step guides on the subject. It is clearly organized, well referenced, and includes everything you need to know to do home wiring projects safely and correctly the first time.

From Library Journal

Electricity is a mysterious (and somewhat scary) subject for most people, even those who complete many of their own repairs. Not so for Cauldwell, a master electrician with over 20 years' experience, who shows how the average do-it-yourselfer can safely perform many tasks usually reserved for electricians. He starts by explaining basic electrical principles and shows which tools to use. A section on inspecting your home's electrical system is particularly helpful, describing various hazards and pitfalls. Other sections cover repairing wiring switches and receptacles and installing light fixtures, ceiling and bathroom fans, and home entertainment systems. Profusely illustrated, safety-oriented, and including sections on troubleshooting and a glossary, this is an excellent title for beginners. Recommended for all public libraries.

Topics include:

incoming black wire, house grounding system, protector box, incoming power cable, splice box, grounding block, incandescent floodlights, grounding slot, one service call, nonmetallic boxes, meter base, grounding electrode conductor, bonding jumper, grounding terminal, ceiling box, grounding bus, pancake box, utility transformer, grounding screw, fan box, main panel, cfm rating, metal water pipes, equipment grounding conductor, professional electrician

Reviews:

Focus on quality and safety: In "Safe Home Wiring Projects," Rex Cauldwell focuses on two things: quality and safety. He shows you how to choose quality receptacles, light fixtures, tools, and other equipment. He also shows you how to do safe, high-quality wiring. While most of us are tempted to buy the cheapest equipment that will get the job done, or buy light fixtures based on looks only, Rex Cauldwell provides good reasons to consider other criteria. The book is well-written and very easy to understand, and the illustrations are numerous and clear. This book is best for those looking for an introductory text -- it covers mostly basic projects, and doesn't cover anything that would involve opening the main panel.

When it comes to electrical wiring, you can't afford to skimp on quality or safety. Armed with the knowledge in this guide, a homeowner can do home wiring confidently, and rest easy with the knowledge that the job was done correctly.

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Double-pole breakers protect 240-volt circuits rated at 1 5 to 50 amps, for appliances like clothes dryers and ranges.

Circuit Breakers (cont.)

Double-pole breakers protect 240-volt circuits rated at 1 5 to 50 amps, for appliances like clothes dryers and ranges.

Ground-fault circuit-interrupters (GFCI) protect people in damp locations from fatal electrical shocks.

Ground-fault circuit-interrupters (GFCI) protect people in damp locations from fatal electrical shocks.

Arc-fault circuit-interrupters (AFCI) de-energize bedroom and other circuits when arcing faults, such as damaged lamp cords, are detected.

Arc-fault circuit-interrupters (AFCI) de-energize bedroom and other circuits when arcing faults, such as damaged lamp cords, are detected.

Standard Edison-base plug fuses (15 to 30 amp) can only be used as replacements in existing installations. Many local requirements mandate upgrading to type S plug fuses; Time-delay plug fuses (15 to 30 amp) will tolerate the quick burst of a high motor- starting current without blowing and needing replacement; Type S plug fuses and their matching permanent adapters prevent the wrong size fuses from being used; Screw-in circuit breakers can replace existing standard plug fuses. When a breaker trips, its button can be reset. These can be replaced by type S fuses for safety; Ferrule-type cartridge fuses, rated up to 60 amps, usually protect large-appliance circuits; Knife-blade cartridge fuses, rated up to 600 amps, usually protect service or feeder wires.
Fuses

Standard Edison-base plug fuses (15 to 30 amp) can only be used as replacements in existing installations. Many local requirements mandate upgrading to type S plug fuses.

Time-delay plug fuses (15 to 30 amp) will tolerate the quick burst of a high motor- starting current without blowing and needing replacement.

Type S plug fuses and their matching permanent adapters prevent the wrong size fuses from being used.

Screw-in circuit breakers can replace existing standard plug fuses. When a breaker trips, its button can be reset. These can be replaced by type S fuses for safety.

Ferrule-type cartridge fuses, rated up to 60 amps, usually protect large-appliance circuits.

Knife-blade cartridge fuses, rated up to 600 amps, usually protect service or feeder wires.

 

Last modified: Saturday, 2007-11-03 1:08 PST