How Does a Circuit Breaker / Trip Switch Work? - Pt 1 

alex tworkowski could do both

SeanBZAThanks, my mistake...adding an annotation now.

SeanBZA Not true everywhere, in parts of Europe (not the UK) the fixed breakers in the board DO protect at least part of the appliance (usually the cord)

***** Not unless the cord is rated to survive. A 20A breaker will do very little to protect a 0.7mm cord ( like on a clock radio) from melting, until it gets to the point where it shorts out, which very well might be well after the fire is raging. On a 1.5mm cord it will provide some protection, but it's main point is to prevent the 2.5mm wiring in the house from burning if say you connect a 2 kW heater to the outlet and then connect a second 2kW one to the same circuit from another socket, then plug in the 1.5kW vacuum cleaner to do the floor.

***** Does this not still happen? (20 amp earth bond test) ?

Have a qualified electrician use a clamp-on amp meter to check the circuit load. If the load is within the limits of the rated breaker, then replace the breaker as they have been known to go bad.

***** did you tell your mom?

Beryllium yes my dear troll

bad formatting, too many tangents. Don't assume they don't like learning.Accept people's criticism.

i think yes .. i work in lab service in summer season there is increase in mcb fault i observed

+Saurav Vats in the event of a high (surge) overcurrent state - say, 100A on a 20A breaker - the solenoid gets energized with enough force to release the latch

Monkeh616 So are you saying that if you have a constant current that the voltage has no bearing on the activation of a solenoid?

mjlorton As far as I know, the voltage won't make any difference to the solenoid, either. It is the current which generates the magnetic field, just as it is the current which causes heating in the bimetal strip. These breakers should operate from practically no voltage (as you would have with a power supply shorted across them in constant-current mode) right up to the point they're incapable of arc suppression. This will not be true of all types, however. AFCIs I believe, certainly GFCI/RCDs, combo devices, devices with programmable tripping characteristics, etc, will require a certain voltage to operate. For bonus points, measure the voltage across the breaker at rated current and determine how much power is lost in it.

Monkeh616 Correct, voltage has no part in the trip on ether thermal or instantaneous trip, the only voltage is developed across the breaker internal resistance, but it is the heating from the current that is activating the thermal bimetal time delay on low overload ( what is being tested here) and the high current through the solenoid coil to pull the internal slug across the magnetic field ( the core of those is a lot more complex than a simple solid metal slug, there is a moving pole piece inside that is pulled into the solenoid coil to provide an impulse to trip the breaker, held in place by a weak magnet in the core) on large overloads, where the thermal trip is too slow to clear the fault before the wire overheats. That is why there are very few purely thermal breakers in house wiring, they require a thicker cable to withstand this overload condition. Here in South Africa the original thermal only breakers from the 1960's required a 4mm cable to ensure it would have enough thermal overload capacity. With the introduction of the thermal magnetic breaker ( as shown here and almost universal in premise wiring protection) you did not need the thicker cable, as it would provide protection to thinner 2.5mm cabling safely. The voltage rating is there for the breaking function, too high a voltage and the arc suppression will not provide adequate arc breaking capacity, which will rtesult in an arc that will self sustain till the breaker burns out and the supply cabling burns off enough that the arc goes out, or an upstream fuse or breaker trips out disconnecting the whole supply. That is why you often have a DC rating so low, as the arc does not tend to go out 2 times per mains cycle, but only when it is either cooled by the arc suppressor cooling off the plasma below the ionisation temperature, or it grows so long that air cooling does that. A nasty demo is to take one of those AC breakers and use a 48V supply from 4 series connected car batteries, where the arc will not extinguish ( though I would not recommend closing the breaker into that but use another larger DC rated switch instead) but will carry on burning even with the breaker opened. I might do a video using a 140A arc welder and a sacrificial 5A DIN breaker, like the ones used, to show that, as I should get a high enough current to make a sustaining arc from that. Going to be fatal for the breaker in any case.

mjlorton Yes, that's the whole point of the constant current setting. In an over-current-limit situation the PSU reduces the voltage below the value you set until the current is at the set limit. I guess in all your tests the "current" LED was on? This means current is the limiting factor and not voltage. And unless you have a very weird PSU you should have seen the voltage on the display drop (to the same value in all of your tests). PSU normally show the real outpur voltage and not the one set under no load. Also how could the voltage make a difference when the current and the resistance stay the same? It's Ohm's law. The voltage WILL make a difference though if it's about extinguishing the spark. At higher voltages it will (obviously) take longer, but that's at values way out of that PSU's ranges.

superdau Yup, thanks for the post. I certainly went down the wrong rabbit hole. I'm going to follow-up with another video covering that mistake. Cheers, Martin.

***** which means that the switch wouldn't hold anymore, right?

TheEnneagram when the contacts of it get dirty by the arc and then you start noticing it heats more than usual with the normal load. That means the contact having resistence.

+TheEnneagram how many times can a circuit breaker break before it breaks?

Andrew Geng How many licks does it take to get to the center of a Charm's Blow Pop?

chines low quality mcb goes crack with 5 to 8 times it trips and high quality breaker keep working again and again ......life long

college is school

Yes. you are correct.