What is Circuit breaker: Definition and 29 Discussions

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. S

    What secondary circuit breaker should I use for my fridge compressor?

    I am replacing a broken inverter compressor with a regular compressor that has the standard electromechanical relay. I plan on controlling the compressor/electro relay with an ac to ac Ssr. The Ssr will be triggered by the condenser fan that is a 110v circuit. The compressor looks like it runs...
  2. kyphysics

    Which Circuit Breaker Switch to Turn?

    My home water heater is messed up. If I want to reset the circuit breaker for it, which should I turn? There are three: 1.) garage (where the heater is located) 2.) water heater/dryer 3.) heat pump
  3. I

    Motor circuit breaker - connections

    Why we use such connection between 4 and 5 terminals? Why the transformer isn't connected via 2 and 4 terminals from CB, the voltage will still be 380V because it's between two phases? In such situation the terminals 5 and 6 will stay unused, why not on this way?
  4. C

    Nanosecond Max Current of Residual-Current Circuit Breaker

    <<Moderator note: Political statement removed.>> To protect against a nuclear EMP (NEMP) usually a big metal box is used, which is electrically connected to earth, to discharge the electrical pulse. Most houses in europe have a 3-grid electric system, L, Neutral (N) and Protective Earth (PE)...
  5. 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...
  6. SW Dad

    UV light + electric current = boom?

    Hi, so I was hoping to get an EE's explanation for what just happened. So my son was apparently over by the light switch pointing a UV pen light at the switch. Suddenly there was very loud, gunshot-like pop, sparks flew, and I had to go reset the breaker. Maybe correlation doesn't imply...
  7. T

    Electronic circuit breaker design

    I'm building an electronic circuit breaker as follows, I have some questions about the short circuit protection. I tested it in simulation and it trips in about 11 ms. How would I work out the interrupt rating ?, which I read is the maximum short circuit current the breaker can interrupt...
  8. T

    Circuit breaker using microcontroller project

    So I am trying to make a circuit breaker using a microcontroller. I managed to get as far as this So I have the CT with a peak detector running to the adc. I then calculate the rms by dividing by root 2, which I then compare with a reference in this case 10A and it trips via the mosfet/relay...
  9. G

    Understanding Circuit Breaker Terminals: IN & OUT Explained

    Why does a circuit breaker not show which terminal is IN and OUT?
  10. Manoj Sahu

    What is meant by electronegative gas?

    Today, one of my professor was teaching about Circuit Breaker and he explained about SF6 circuit breaker. He told us that SF6 is electronegative gas. But i really didn't understand what is electronegative gas. Please can someone explain in detail. Thanks in advance.!
  11. marellasunny

    Alternatives to varistors as overload protection at DC motor

    Alternatives to varistors as overload protection at DC motor DC Motor here implies 12V linear actuator w/DC Motor that consumes 2.8A under loading condition. Pretty costly equipment. I'm using a L298N motor driver connected in parallel to run the linear actuator. The motor driver is run by a...
  12. P

    Is the circuit breaker amperage the rms amperage

    The circuit breakers of my house say that they are 15a (the majority of them). The rms voltage is 120v for the outlets, and so the peak voltage is about 170v. I was wondering, if I hypthetically connected the terminals together with a 10 ohm resistor, would the breaker trip? I don't know if the...
  13. J

    Adding extra socket share with water heater power supply

    It is safe to add on extra socket by this way? Original connection: postimg.org/image/v6nshoygh/ Add-on connection: postimg.org/image/vkoccsyu5/ The extra socket is for light usage only. Water heater is instant water heater without tank. The switch is double pole single switch.
  14. 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...
  15. EverGreen1231

    High Power Circuit Breaker Operational Reliability Question

    My supervisor asked me Friday if there were any way to determine the operating reliability of a large circuit breaker in a Substation. Now, to me (just having thought about it a little over the weekend), it would seem that breaker reliability of operation would really have to be something that...
  16. K

    Circuit breaker, clearing a fault current

    hi could someone please explain the attached circuit to me in detail. From what i understand: the open circuit caused by the opened switch in series with the resistance causes a fault current in the system. This higher than normal current across the 200 ohm resistor causes a high...
  17. K

    Solid state DC circuit breaker to protect a load

    My choice of solid state Dc circuit breaker is the Mosfet, easily available( i got loads!) i want the mosfet to interrupt the circuit to protect the load from overvoltages This is what I've done so far, please help its not working the way i want it to. note to mods: i also put this...
  18. K

    Solid state DC circuit breaker, used to protect a load

    My choice of solid state Dc circuit breaker is the Mosfet, easily available( i got loads!) i want the mosfet to interrupt the circuit to protect the load from overvoltages This is what I've done so far, please help its not working the way i want it to. the resistor connected to the...
  19. N

    How circuit breaker electrical system clears ground faults.

    Hi I am taking generals now but I will eventually take EE degree. I am studying electrical systems now. Can somebody help me on system configuration regarding circuit breakers clearing ground faults? In this picture (the bottom figure), if X2 faults at the transformer, would the fault...
  20. C

    Why circuit breaker shuts off when lamp burns out?

    Isn't the case that when the lamp filament melts the resistance of that part of the circuit goes to infinite? So why does the circuit breaker turn off current? Thank you Regards
  21. M

    Why we use motorized circuit breaker?

    hi all... i want to know you buddy.. why we use motorized circuit breaker along with under voltage trip (utp) and how motorized circuit breaker works along with under voltage trip (utp)... i want to know briefly about this procedure... your answer will be appreciate. thanks advance...
  22. M

    Circuit Breaker Ratings and Electrical Protection

    Hi, I am student electrical engineer and I should probably know this stuff but I am trying to work out how to determine the required short circuit current rating of circuit breaker, I have seen in the Schneider Electric catalog 'determination of short-circuit current" using cable data and...
  23. Redbelly98

    Circuit breaker with parallel resistor

    In my battery-powered lawnmower there is a circuit breaker. I have replaced the breaker, and when I cut apart the old one I found a 68 Ω resistor in parallel with the breaker switch. My question is, what is the purpose of this resistor? Here is the basic mower circuit: (Imagine that...
  24. Ed Aboud

    What caused my circuit breaker to fail and why is there a 50A fuse?

    Hi all! I have an issue with the circuit breaker in my house and was wondering would anyone be able to shed some light on what's going on. So last night, I plugged in the hoover and all the electrical devices in my house switched off. I wasn't surprised as I had many devices on at the time so...
  25. A

    Circuit Breaker Sizing for Distribution Board (D.B1 & D.B2): Confusion Resolved

    I have Distribution board, Outgoing (D.B1) But I got confuse for MCB sizing: The busbar 400V, 125A, 50Hz, 4P, 10KA for 1Sec. The part of Outgoing Rates as the followings: Feeder-1: 2.5 KVA used 25A MCB 2P Feeder-2: 3.5 KVA used 25A MCB 2P Feeder-3: 2.0 KVA used 25A MCB 2P Feeder-4...
  26. S

    My Circuit Breaker is Miswired - What Should I Do?

    So I'm getting my water heater changed and my circuit breaker is probably wired wrong because we had to flip a bunch of switches not labeled "water heater" to actually shut the power off. One thing I didn't really get was why one switch shut down the voltage between the red and black wires, but...
  27. B

    Catastrophic failure SF6 Circuit Breaker

    We have had a catastrophic failure of an SF6 circuit breaker. This breaker was used as a synchronising breaker for a CHP on our 11kV system. Does anyone have or can point me to articles on failures (causes & effects) of SF6 circuit breakers. TIA
  28. I

    English Electric's OBX3 Circuit Breaker

    Hi there.. I'm righting this thread hoping that anybody can help regarding a specific issue. I'm looking for English electric circuit breakers (OBX3) that whore installed in the late 60's in circuits for heavy Industries, more specifically for the steel coil industries. I would like to...
  29. I

    Engineering English's Electric OBX3 Circuit Breaker

    Hi there.. I'm righting this thread hoping that anybody can help regarding a specific issue. I'm looking for English electric circuit breakers (OBX3) that whore installed in the late 60's in circuits for heavy Industries, more specifically for the steel coil industries. I would like to...
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