Neutral lead on RCBO'S

[Kev2632]

What exactly are the neutral leads for? and if a neutral to earth happened on a board with just RCBO'S in it, why doesnt the fault travel along that neutral and affect the other RCBO's?

 

[Darkwood]

arty:

 

[Kev2632]

Thanks for the drawing there, so in that set up in will trip the rcbo1 yea? As it senses an imbalance yea ?

 

[Knobhead]

If you look I've put the currents in the various legs. So yes there out of ballance.
Either could trip, both are out of ballance.

 

[Kev2632]

Yea ive noticed that yea, so what I'm wondering is would both rcbo trip or would it just be one? As they are both out of balance??

 

[Knobhead]

You got in before I finished editing my last posy. It'e a ---- up which trips.

 

[Darkwood]

Just to re-iterate kev, when one trips it effectively isolates the other rcbo from the fault so usually on one trips, but occasionally it can trip both together but its rare as background leakage on the circuits will put one rcbo closer to the threshhold than the other as well as trip times and mA needed to trip will very slighty from rcbo to rcbo.
So in a nutshell, several factors are in play as to which one is gonna trip thus its rare for them to trip together, and after one has tripped it blocks the return path so the other rcbo holds.

 

[Kev2632]

Just to re-iterate kev, when one trips it effectively isolates the other rcbo from the fault so usually on one trips, but occasionally it can trip both together but its rare as background leakage on the circuits will put one rcbo closer to the threshhold than the other as well as trip times and mA needed to trip will very slighty from rcbo to rcbo.
So in a nutshell, several factors are in play as to which one is gonna trip thus its rare for them to trip together, and after one has tripped it blocks the return path so the other rcbo holds.

Thanks very much Darkwood,

So the reason the path is blocked is because the Neutral has been shut off with RCBO tripping yea, and isnt able to travel back along the neutral lead to the other rcbo? Is that correct?

 

[Darkwood]

Thanks very much Darkwood,

So the reason the path is blocked is because the Neutral has been shut off with RCBO tripping yea, and isnt able to travel back along the neutral lead to the other rcbo? Is that correct?

Correct!

 

[Kev2632]

Correct!

Thanks, i was just having a looking at that drawing there on page two tony drew, say for instance there was a neutral to earth fault on RCBO 1 , and it trips RCBO 1, then on RCBO 2,Current flows up the live and back down the neutral as normal, but wont any current flow across that neutral link and touch the earth fault? or how will that work???

 

[Knobhead]

In that instance both will trip.

View attachment 11925

 

[derek preece]

As far as I understand it, if there is an N/E fault on RCBO1 and RCBO2 shares a neutral on the load side then RCBO2 will also see an Earth fault and so it will trip.

 

[Kev2632]

In that instance both will trip.

Yea thats what i thought yea, and that would happen no matter regardless of what you do there, until that borrowed neutral would be removed and then the N-E fault would only lie on RCBO 1 yea??

 

[Knobhead]

Hope you can see the fault direction arrows on the last drawing

 

[Kev2632]

Hope you can see the fault direction arrows on the last drawing

Thanks Tony you've been a massive help cheers

 

[Geoffsd]

As far as I understand it, if there is an N/E fault on RCBO1 and RCBO2 shares a neutral on the load side then RCBO2 will also see an Earth fault and so it will trip.

Correct.

A borrowed neutral N-E fault will trip both because both neutrals (or shared one) will be connected to earth.


Just to point out that single-module RCBOs are only single-pole switches.