Circuit breakers Definition and 14 Threads

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. Its basic function is to interrupt current flow after a fault is detected. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliance, up to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, or fuse, as an automatic means of removing power from a faulty system is often abbreviated as OCPD (Over Current Protection Device).

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  1. G

    Circuit breakers trip on *power* overload?

    Old style electrical panels protected residential circuits with fuses which tripped (and were destroyed) when the internal wire got too hot and melted. What is it exactly that causes a modern residential circuit breaker to trip? They are rated by amps, but heat correlates to power (volts x...
  2. K

    Tripping Behavior of Circuit Breakers

    For US residents. If you have the above circuit breaker put in your panel phase to phase (2 pole).. and one of the phase touches neutral.. would the circuit breaker trip or not? It's rated 240 volts.. yet one pole only has 120 volts.. would that 120 volts shorting the neutral trips it? This...
  3. Manoj Sahu

    Difference between a circuit breaker and a load break switch?

    Hi. I am working in on a Ring Main Unit of Siemens make. Today, my senior asked me the same question. As per my understanding, a circuit breaker is make or break switch. I mean, when fault occurs the circuit breaker trips, protecting the equipment connected to the line. I have no information...
  4. Michael George

    A circuit breaker does not work properly?

    I live in Egypt where we use 220V AC / 10 A. When I turn light off at a circuit breaker, all lights turn off but both mains ( hot & neutral ) become hot. When I test them, they both have electricity (live), so I afraid to touch them. I would expect that they both become neutral ... Why does that...
  5. E

    NEC: Outlet Rating on 20A Breaker? Current Per Outlet?

    If you have multiple outlets connected to the same 20A breaker, do the outlets need to be rated for 20 A? Or, is it acceptable to have the outlets rated somewhat lower? Where can I find this information in the NEC? If I do not need each outlet to be rated for 20 A, then is the current rating...
  6. M

    Static electricity and circuit breakers

    Hi I have seen electric technicians while racking out high tension circuit breakers, use a wire that has one end grounded and they use the other end to touch the bus bars on the breaker in case of a static charger, they carry out this procedure before they do any work on the CB in case they...
  7. J

    Understanding Circuit Breakers: How They Work and Why They Are Important

    Here is my attempt at explaining how a circuit breaker works, is it correct? A circuit breaker works due to the residual current - the difference in current going through the live wire and passing out through the neutral wire. Normally, the current going in and out of a system is equal so...
  8. S

    Why do circuit breakers blow when all machines are started at the same time?

    Homework Statement In a certain machine shop, if everyone starts their machines at the same time circuit breakers will blow, even if all the machines can normally operate simultaneously. Why? Homework Equations N/A The Attempt at a Solution I know that typically direct current is...
  9. S

    I have questions about circuit breakers .

    Welcome everybody in this forum. I would like to ask about Oil circuit breaker, there is a dielectric strength test of its oil so, I want any documents about that, containing the voltage that the oil will breakdown in it , accents of oil that has been broken down and the name plate of the oil...
  10. I

    Understanding Circuit Breaker Hierarchy in Power Distribution Networks

    In a normal power distribution network there are successive circuit breakers each responsible fore the circuit that lies below them. Now suppose i assume that there is a short circuit in my house then shouldn't the circuit breaker that lies above the MCB in my house, maybe an ACB or MCCB in...
  11. D

    Calculating the Ampere Rating of a Circuit Breaker

    The problem statement: To save on heating costs, the owner of a greenhouse keeps 800kg of water around in barrels. During a winter day, the water is heated by the sun to 50 degrees Fahrenheit. During the night the water freezes into ice at 32 degrees Fahrenheit in 10 hours. An electrical...
  12. D

    Circuit Breakers - tripping or not tripping?

    The problem statement: To save on heating costs, the owner of a greenhouse keeps 800kg of water around in barrels. During a winter day, the water is heated by the sun to 50 degrees Fahrenheit. During the night the water freezes into ice at 32 degrees Fahrenheit in 10 hours. An electrical...
  13. G

    Circuit breakers and short circuits

    Homework Statement Hi, This isn't so much an actual problem, just more of a general question. Can anyone give me a layman's explanation of what a short circuit is and how a circuit breaker deals with that? Or, can anyone refer me to any sources that can? I have taken high school physics...
  14. V

    What is the Formula for Sizing Circuit Breakers?

    Hi all, I am curious to know if anyone can provide me with a formula or a rule that sizes the circuit breaker so the circuit is protected during inrush currents. The supply is 415VAC, 50Hz. The current comming from the buildings main distribution panel is around 60 Amps. The...
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