Why Circuit Breakers DON'T Protect People (electric shocks)

How do miniature circuit breaks (MCB) work and why do they protect cables not people. What makes the trip, what happens inside, where are they used and how do we read the charts.

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[EngineeringMindset]

*This free video took weeks to make!* if it helped you and you'd like to thank or support Paul's efforts, link below:

[thomasvlaskampiii]

The fact that you replied to my comment from 3 years ago and gave a link to this video was a nice gesture. I appreciate it

[xTerminatorAndy]

This is a gold standard for showing how breakers work. Very pleased with that

[TishaHayes]

As an electrical engineer I have repeatedly attempted to explain circuit breaker operation and curves to technicians and electricians. No matter how extensive (or simplistic) I make my explanation it ends up with them offering up a sceptical look and them just accepting the answer without really gaining an understanding.
This is an excellent video; I shall share this as the teaching video for breakers.

Thanks so much for putting the effort in to creating it.

[tuckkeongho]

This is about the best video explaining how a MCB works. Well done.

[TheEulerID]

The title is a bit misleading. True, MCBs do not protect people from fatal electric shocks. However, they do protect people from electrical fires due to overloads and, statistically speaking, electrical fires have been a much killer of people than electric shocks (particularly in the USA I should add, partly because of the way they build houses). To say that it is just there to protect property is simply not the case. Also, some MCBs are twin pole, although that's more an industrial and European domestic thing (at least in some countries).

However, excellent job at explaining how MCBs work, and especially the dual-mode switching and why it's done that way.

I note, there is still no mention of RCBOs. Those dual RCD consumer units are, thankfully, rapidly being confined to history and many electricians will no longer quote for split RCD CUs, and I'm a bit surprised that the regulations still allow them. Of course, then we come onto a far more contentious point, which as AFDDs.

[JoaoVictor-hzrm]

I'm loving this more live-action kind of videos

[somedude]

They’re not meant to protect people, they’re meant to protect circuits. That’s why they’re called “circuit breakers” and not “people protectors”.

[AtAGlimpse_UB]

Dude, the transitions are so freaking mind boggling! Great Job Paul!

[JackCobalt]

I'm glad you said qualified and competent at 4:20, because I've seen a lot of people who are competent who think they're qualified, and people who are qualified but aren't quite competent 😂😂

[gg-gnre]

@13:00 good to add that the arc chamber is "up" aka away from gravity. The arc travels up as heat rises due to gravity. If you install breakers upside down you can actually get good arcs to melt internals instead. It's a fun exercise lol
awesome video as always

[jhanthony]

Those circuit-breaker graphs are great! I learned a lot from this.

[rahul]

bro have one of the best engineering channels i have learnt a lot from you despite being a mechanical engineer myself about electrical as i also had a specializing in automation

[Sirius-]

The level of content is just impressive. The pace in the video absolutely matches my learning pace, not too slow or fast, just perfect. I wish there were more creators in every field like you. Thanks for the amazing content man.

[allangibson]

MCB’s can be safely mixed because they are designed to a common mechanical and electrical standard. Different manufacturers only becomes an issue if a distribution comb is used but that can even be an issue even with in a specific brand.
The leading letter refers to the trip curve which goes beyond B, C and D - “A” being fastest and “F” being slowest (and usually used for variable speed motor circuits (and occasionally switch mode power supplies with high inrush currents).
C curve breakers are the most common in domestic use.
Direct On Line started motors typically draw seven times the running current during start.
Hard Start Switch Mode Power Supplies draw their full output load current during starting - so a 5V 1000A supply will draw 1000A for the first fraction of a cycle until the output reaches 5V - so from a 240V supply 240kW (and having tripped a gas fired power station offline by turning on a computer system, this could happen (steady state the system drew 1kW - the power supplies were oversized and redundant (2off)).

[zentrobi]

As en electrician, i just wanna confirm that this is proberbly the best explained video of a Circuit Breaker that i have ever seen. will definately be showing this next time an apprentice asks or anyone else for that matter.

[paulswearingen]

Great explanation and demonstration of the operation of a thermal magnetic breaker.
However, I think it’s worth mentioning that circuit breakers do protect persons from electric shock - with proper grounding and bonding practices.
The most likely scenario for a person to come into contact with an energized conductor is if said conductor has inadvertently touched a conductive casing that is not meant to be energized. When a person touches that casing their body is the current path for the fault (for any electrical system that uses earth as neutral). As you pointed out, fault current through a human body may be too low to trip the breaker and you end up being an unwilling conductor for much too long.
To solve this issue, electrical systems are required to be properly grounded and bonded. This means that when metal casings (or other non current carrying conductors) are bonded to a conductive grounding system and become energized, the fault will now travel with low resistance through the grounding system, produce high current, and trip the associated breaker; thus preventing an electric shock.
I really appreciate your content and just want to add some clarity to your title.

[__u__]

This was easily the best video I've ever seen on this topic in my whole life. Top tier quality right here

That's why we use 30 mA differential breakers in Europe.

[arjun-vhnp]

You are the only electrical engineer i have noticed explaining the breaker selection chart clearly and neatly....do more videos brother keep it up....