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?

 

[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.

 

[Kev2632]

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.

But arent most RCBO'S double pole switches?

 

[Geoffsd]

No. Not the ones normally in CUs.

 

[Kev2632]

No. Not the ones normally in CUs.

So how is the neutral isolated then when the RCBO trips?

 

[Geoffsd]

It's not.

That's why it trips when you touch N and E.

Edit - no that only applies to RCCBs with an MCB off.
RCBO already off

 

[Kev2632]

It's not.

That's why it trips when you touch N and E.

Yea but on page 3 there, Tony and Darkwood was saying that the neutral would be isolated ?? what is right then?

 

[Kev2632]

So when the rcbos are single pole devices then, what would in the scenarios we have described with the borrowed neutral case, and the borrowed neutral with the N-E fault on Rcbo 1? What happen in both of these scenarios?? :/

 

[Geoffsd]

No. It's not isolated.

So, if borrowed or connected to another neutral it will divert current from the second RCBO.

If there is an N - E fault it will be on both RCBOs.

 

[Kev2632]

No. It's not isolated.

So, if borrowed or connected to another neutral it will divert current from the second RCBO.

So the current will travel back along RCBO1 Neutral cable through the neutral lead and trip also the RCBO 2 is that correct??

 

[Geoffsd]

Yes...

 

[Kev2632]

Yes...

So just to clear this up for the single pole RCBO, in relation to the drawing on page 3- bearing in mind they are single pole RCBO's instead, when we have just a borrowed neutral on RCBO 1 & 2, It will trip both RCBO, when RCBO 1 trips the current will go down through RCBO 1 neutral cable, through the RCBO1 neutral lead and trip RCBO 2 as well yea?? and when we have the borrowed Neutral and neutral to earth fault on RCBO1 it will trip RCBO1 and will it no affect all the other RCBO's as well now??? as the neutral is not isolated from the rest of them??

 

[Kev2632]

??? anybody keen to answer that ^^ please

 

[Geoffsd]

So just to clear this up for the single pole RCBO, in relation to the drawing on page 3- bearing in mind they are single pole RCBO's instead, when we have just a borrowed neutral on RCBO 1 & 2, It will trip both RCBO,

Yes, because the current is going out through one RCBO and (some of it) back through another - so imbalance.

when RCBO 1 trips the current will go down through RCBO 1 neutral cable, through the RCBO1 neutral lead and trip RCBO 2 as well yea??

Yes, probably at the same time if lamps on both circuits turned on.
It's easier to see if you draw the circuit and follow the current path(s).

and when we have the borrowed Neutral and neutral to earth fault on RCBO1 it will trip RCBO1 and will it no affect all the other RCBO's as well now??? as the neutral is not isolated from the rest of them??

Not sure if you meant now or not.

Don't forget that an N-E fault will only trip the RCBO whose neutral has faulted to earth and the one whose neutral is connected to the neutral of the first - not any others because the fault is on the load side and load side neutrals are not connected (except in these fault conditions).

 

[Kev2632]

Yes, probably at the same time if lamps on both circuits turned on.
It's easier to see if you draw the circuit and follow the current path(s).

So the current wont travel back up the supply side of an rcbo then?

Not sure if you meant now or not.

Don't forget that an N-E fault will only trip the RCBO whose neutral has faulted to earth and the one whose neutral is connected to the neutral of the first - not any others because the fault is on the load side and load side neutrals are not connected (except in these fault conditions).

Yea i meant now sorry, ahh right so once the RCBO 1 has tripped the fault is isolated from the rest of the circuits as the current wont get past the supply side of RCBO 1 yea??

 

[derek preece]

Sorry just read your last post so edited mine

 

[Geoffsd]

Yes, as no other circuits are connected to it (unless by these faults) none of the other RCBOs will be affected.