Rcd

[Monkeyblaine]

I recently got a belt (don't laugh) from what I'm sure was between live and earth and the circuit was RCD protected. Now if they are so sensitive can someone explain why it didn't trip. Also same question between live and neutral and the cb not tripping.

 

[telectrix]

insufficient leakage current to trip RCD. MCB will not trip on earth leakage, it requires a much higher current.

 

[Rockingit]

An RCD will trip on a human being, I know, they've saved my bacon on several occasions over the years! It just depends on how much current is allowed to flow in that moment - for example, last time it happened to me was a 'cross the body' (as in from hand to hand) so that's quite a lot of me which means quite a lot of current, whereas a 'brush with a fingertip' might not last long enough or be of insufficent conductivity. A typical 30mA RCD will trip at around 20-25 mS so that's still 3-4 full waveform's worth of juice.

By comparison, an MCB needs much more time and current to work - and even if it was only a 3A device then you'd be a real mess by the time it worked.

What do we learn from all this??........Safe Isolation!

 

[Monkeyblaine]

Haha very true. Thanks guys for help.

 

[Farmelectrics]

no live working as the niceic say

 

[snowhead]

I can also personally confirm that cross body finger to finger does cause pain, and embarrasment when you've just told someone it couldn't have happened on an RCD protected Cct.

I'd much prefer back of the hand in a control panel, at least you expect them.

 

[MarkieSparkie]

A high sensitivity (<30mA) RCD does not prevent a person receiving an electric shock. If the impedance of the fault path is low enough that sufficient fault current flows to trip the RCD it should limit the duration of the shock such that serious injury or fibrillation does not occur, but other forms of minor injury may occur eg. from dropped tools or a fall from height. However, the actual nature and effect of an electric shock depends on many factors - the age and sex of the victim, preexisting medical (heart or skin) conditions, which parts of the body are in contact, whether the are other resistive elements in circuit eg. clothing or footwear and if either of their contact points are damp or immersed in water.

 

[Darkwood]

i changed a mcb to rcbo for some bench sockets in a workshop and was questioned if it was necessary to which i explained, a week later i saw a guy pick a drill up that was plugged in and slam it down in a strange manor, he said he got a belt and sure enough 1 tripped rcbo and a faulty drill, i quickly expalined to him had he done that the week before i might have been humming a bee gees tune while doing chest compressions, now he appreciates the rcd protection, i do feel good when my work has a late appreciation