K
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?
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because the neutral from the circuit being fed from the RCBO has to go through the RCBO before it gets to the neutral bar vie the RCBOs neutral lead.....so any imballances due to fault between neutral-earth are seperated from the other RCBOs/RCDs within the install....unless in series of course
Q1 to complete the circuit
Q2 because only one rcbo will detect the imbalance and trip.
because their pigs TC...And why do they have curly neutrals so you can't do a neat job!
Whether post in humour or not the reason is its fine wire and to terminate it it has to be crimped, the factory crimp it for you but if it was just one long lead ppl would shorten it more readily and probably ignore the regs and not crimp, this has a risk of poor termination which can cause overheating, nuisance tripping etc etc, the manufacturers would get more returns thinking rcbo faulty because of poor terminated neutrals due to sparkies cutting long leads to length.And why do they have curly neutrals so you can't do a neat job!
RCBOs have flying neutrals that terminate into a common neutral bar...yes?....so as the final circuit is connected THROUGH each individual RCBO....both line AND neutral.....so the RCBO will detect imballance without upsetting the ballance of any other RCBOs within that C/U....
A - if there was a borrowed neutral then this would trip the rcbo anyway as there is an imbalance of load out and return as the current would be higher on the return path when borrowed neutral load was switched on, but hypothetically if you could maintain the circuit and and then touch down neutral to earth it will only trip the rcbo that is leaking the current and has seen an imbalance, this will depend on many things like where the short is, cable resistance , volts drop etc etc all playing a part in where the neutral current will leak to and how much, its possibly alot more complicated than it should seem.Yea i understand what you mean, what I'm meaning is if there was a borrowed neutral on the load side of the rcbo " a link between two rcbo e.g on two lighting circuits" and there was a earth to neutral fault on one rcbo why won't that affect the rcbo number two ??
Also in answer to your question is that when the rcbo trips it will stop the current flowing in the borrowed neutral so the second rcbo dosen't see it, which rcbo trips will be down to the variables mentioned above.A - if there was a borrowed neutral then this would trip the rcbo anyway as there is an imbalance of load out and return as the current would be higher on the return path when borrowed neutral load was switched on, but hypothetically if you could maintain the circuit and and then touch down neutral to earth it will only trip the rcbo that is leaking the current and has seen an imbalance, this will depend on many things like where the short is, cable resistance , volts drop etc etc all playing a part in where the neutral current will leak to and how much, its possibly alot more complicated than it should seem.
So it is possible for two rcbos to trip if somebody borrowed a neutral from two different circuits and there was neutral to earth fault on one circuit yea?
And why do they have curly neutrals so you can't do a neat job!
In this set up one rcbo will trip a majority of the time, once it trips it isolates the link to the other rcbo through its double pole switch, although its possible that once in a blue moon they could trip together as you have to remember that if once rcbo gains extra neutral current then the other rcbo will loose it and both are out of balance, but also to take into account is natural leakage existing so the rcbo that has a higher background leakage will operate the first and as mentioned before it then isolates the link between the 2 neutral leaving the other rcbo on.I'm talking about 2 individual rcbo detecting there own circuits what happen if the neutral from rcbo 1 happened to join up with rcbo 2? As in they have borrowed a neutral from circuit 1 and it used at somepoint in circuit 2 would that trip both rcd as the neutrals are mixed up or does it not matter as its one common neutral bar for the installation??? Sorry im just getting confused and cant get my head round this
By Jove i think you got it! correct.... !!!!!!Yea thats probably what it is, neutrals of the same circuit yea? But for example If the neutrals of different circuits were all joined together in 1connector block that will not work ? Because they are fed from two different rcbos is that correct yea? And the rcbo will see an imbalance is that right? Thanks so much for your help so far
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.
Correct!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!
In that instance both will trip.
Hope you can see the fault direction arrows on the last drawing
Correct.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.
No. Not the ones normally in CUs.
It's not.
That's why it trips when you touch N and E.
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