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

[JoeRoy]

[AVGresponding]

Errm, because they aren't intended to? Circuit breakers are intended to prevent the wiring from becoming a fire hazard, nothing more.

GFCI/RCD/RCBO are the devices intended to protect people.

[Gyro]

It's quite a good video description and operational demonstration of the internals of an MCB. Of course the MCB is a an overcurrent device (replacing the older consumer unit fuses) and has nothing to do with shock protection. The video does show the internals of a UK split-load consumer unit and shows the RCDs in place, but doesn't describe their role in protecting against current leakage and shock.

There must be another video in the series that describes the purpose and operation of RCDs.


EDIT: In fact he describes it in this video...



Maybe he will go on to produce a video of the RCD internals at some point. Most new UK installations now include RCBOs, which combine the function of MCB and RCD on each individual circuit.

[Zero999]

I don't have time to watch those videos.

It's not completely true. Before the advent of RCDs and RCBOs, circuit breakers and fuses certainly did some provide protection against electric shock. When the line conductor makes contact with a a piece of equipment's earthed case, the over current protection device has to quickly interrupt the current in order to keep the voltage on the exposed metalwork form reaching a hazardous voltage. If there's no RCD and inadequate over current protection, then it's possible for exposed, earthed contactors to reach a hazardous voltage, under fault conditions.

Nowadays, RCDs and RCBOs provide protection against shock from earth leakage, so the role of over-current protection is mostly to prevent fire, but it's still good to have another layer of shock protection.

[EPAIII]

Ah, but by preventing fires,

THEY DO PROTECT PEOPLE.

[tom66]

RCDs also prevent fires.  One of the original justifications for RCDs was detecting rodent damage to tasty cables.  A rodent could chew through a cable and create a path from live to earth which might be insufficient to trigger an MCB but the imbalance would quickly trip an RCD.

This is a particular issue in lofts.

https://www.electrical-installation.org/enwiki/Protection_against_fire_due_to_earth_faults

[AVGresponding]

RCDs also prevent fires.  One of the original justifications for RCDs was detecting rodent damage to tasty cables.  A rodent could chew through a cable and create a path from live to earth which might be insufficient to trigger an MCB but the imbalance would quickly trip an RCD.

This is a particular issue in lofts.

https://www.electrical-installation.org/enwiki/Protection_against_fire_due_to_earth_faults

Yeah, take that article with a pinch of salt; it's by Schneider Electric.

[mendip_discovery]

Why does everything HAVE to be a video these days, and then damned lazy posting it to a group.

Anyway, as someone who has taken a few 230V AC shocks and even one rather bracing belt with a few kV. The time you are exposed does make a difference. 10 ms compared to ∞ (or how long before the power is cut) is often the difference between walking away or not.

[Gyro]

Yeah, take that article with a pinch of salt; it's by Schneider Electric.

Better that than Hager. 

[AVGresponding]

Yeah, take that article with a pinch of salt; it's by Schneider Electric.

Better that than Hager. 

I wouldn't trust any manufacturer to not try to use the opportunity to sell you their product.

[Andy Chee]

The time you are exposed does make a difference.

If the electric current is enough to contract your muscles and grip that live wire with even greater strength, of course the exposure time is only going to increase.