Dangers from the neutral

[oldtimer]

Yes oldtimer it does,
However, it does not disconnect the neutral in the event of a fault.

I cannot understand the preoccupation with breaking the neutral remember a RCBO is a circuit breaker and RCD combined just accept the fact that when you switch a RCBO off it does the same as any circuit breaker ie it breaks the live but the neutral is intact dont get bogged down with this as it will only distract you

 

[netblindpaul]

I believe it comes from the requirement to isolate all live conductors on a TT install.
However, this is not explicit wrt disconnection in the event of a fault, only for isolation in the regs.
It is open to interpretation.
This is due to the fact that the N on a TT may not be at earth potential.
There are times when the N of a TN especially a TN-C-S may not be at earth potential, but in the regs this is considered less of a chance.

 

[telectrix]

so, paul, if you were installing a RCBO board on a TT system, would you then specify 2 pole RCBos, or rely on the main switch for 2 pole isolation?

the reason i ask is: if working on a circuit, you may want to isolate that one circuit while working rather than having to isolate the whole board.

 

[netblindpaul]

Given the choice I would always use 2 pole protective devices on 1ph & 3 or 4 pole on 3ph final circuits however...

Now if we are talking domestic, unless you have someone at home on life support there is no reason to work on a domestic install with the power on to the board, you should be able to isolate the board.

BTW if you have someone at home on life support then there will be other things to consider!!!

Come commercial/industrial, then other issues come into play.

However, it is never this cut & dried.

I have trawled through the regs and I believe that only 1 pole protection is required.
However 2 pole isolation IS required in the regs.

In a domestic situation, what is wrong with killing the whole board & disconnecting the L&N from the board internally, making safe and re-energising. Work on the circuit and then undertake the converse?

 

[ackbarthestar]

Many modern RCBOs have dedicated outgoing neutrals, try and cross them and see what happens to the RCBOs of the two crossed circuits.
The only common reference is the earthing bar.

The double pole isolation factor would be applicable to certain types of installation. However, as Telectrix states they are useful for independent final circuit isolation.

 

[La Poste]

I can't decide if I'm being overly paranoid but I just like the idea of double pole isolation.

Single pole RCBO's just don't seem right to me but then I am a bit of a novice so maybe I am worrying about nothing.

 

[i=p/u]

well they ,ake them available like that so you isolate whole board and DO NOT WORK LIVE.....

 

[oldtimer]

Thats it I am unsuscibing from this post

 

[La Poste]

Thats it I am unsuscibing from this post

Was it something I said?

 

[La Poste]

I have trawled through the regs and I believe that only 1 pole protection is required.
However 2 pole isolation IS required in the regs.

Why do you think this is?
Why is double pole isolation necessary?

Is it because of the potential danger within the domestic installation arising from shared or crossed neutrals or is it because of some danger from outside of the installation, a potential danger imported from the network by not isolating the neutral?
If that makes sense?

Why is double pole isolation necessary when single pole circuit breakers are said to be safe?

As you can see my knowledge of the network is very limited.

Thanks.

 

[ackbarthestar]

Thats it I am unsuscibing from this post

Yes, Friday can be a bit of a shock to the initiated :45: arty:

 

[netblindpaul]

In a TT system, the N is not considered to be tied to true enough E, so you must 2 pole isolate.
In a TN system, you must isolate all live conductors is unskilled persons are likely to work on the install basicallt.
Check in the old red book, regs group 537.

 

[Deleted member 26818]

Double pole isolation is required, to guard against reverse polarity.
It is also guards against a difference in potential where there is a high resistance between the earth and the neautral.