safe to work on a circuit isolated with MCB?

[gsalerni]

Hi,
Just a quick safety question. Having turned off a circuit at the consumer unit via the MCB for that circuit e.g. a ring main or a lighting circuit - is it safe to work on that circuit e.g. adding another socket into the ring? Obviously haven taken steps to ensure someone can't accidently turn on that circuit again while your working on it!
I ask becuase from what I can see the MCB only isolates the live wire - the neutral is still connected to the block and other circuits will still be live?
Of course I could turn on the CU at the main two pole isolator but then that takes every circuit out which is a pain but which I'll happily do if there is a real risk in only isolating via the MCB.
ta.

 

[breezer]

other circuits as you said will still be live, before you work on any circuit you should always insure that it is dead before you are.

It is a possiblitity that some one has wired the neutral and live the wrong way round, you turn off mcb and the live is still present ( and live)

I would suggest running in and connecting all the "dead ends" first, then make your connections last, after isolating the supply, bearing in mind what i have previously said

 

[nstreet]

Would you take the top off of a plug and work on it whilst it is still plugged into the socket, even though its switched off? Probably not.

Why not disconnect the ring at the CU.

 

[bushynut]

unless some one who installed the lighting circuit originaly confused the nuetral and phase conductors it'lle be safe.

The nuetral takes the current away from the circuit, so to power a light the circuit would go consumer unit> phase> ceiling rose> nuetral> consumer unit and phase passes through the light and out through the nuetral.

Personaly i'd turn the consumer unit totally off. 'cause you never know

 

[AliasOmega]

If unsure, you could get your multimeter on the socket to check the power supply.

If in doubt, turn the whole board off...

 

[breezer]

i said that 3 posts ago

 

[gsalerni]

thanks for the quick response guys. yes hadn;t considered the possibility that that circuit or indeed one of the others might not be wired correctly - I was thinking mostly about whether there was any risk between neutral and earth on the cicruit even without live for that circuit being present.
P.S. bushnut - what is a phase conductor.
Anyway think I'll play it safe and turn the whole board off - not too great a hardship to go round resetting video clocks and the like.
many thanks.

 

[Damocles]

Biggest risk might be that while working on the socket with your electically powered light from a different circuit, you short out neutral and earth. Result is RCD trips and turns off all power... leaving you staggering about in the dark falling over nasty sharp things and falling through those missing floorboards.

 

[AliasOmega]

When i do carry out DIY around the house..aka moving sockets, lights etc..if the kids are getting on me nerves, i do short neutral - earth to trip the RCD therefore giving them no more light to annoy you...

Remember to have a torch handy tho..so you can work in the quiet..

 

[steve190]

Phase (also known as Live)

 

[breezer]

perhaps i should expand on that.(in leymans terms)

Electricity is generated using 3 coils, each coil is 120 degrees from the previous coil (all coils are in a "circle ", 3 x 120 = 360, full circle)
as mentioned each coil is 120 degrees from the other,that is to say they are 120 degrees "out of phase" which gets shortend to "phase"

 

[steve190]

And each coil is marked as

Red, Yellow, Blue or L1, L2, L3 or X, Y, Z orr similar.

But as this only affects 3 phase systems and most households are 1 phase we don't need to wory about the phase identification or at what angle of rotation it is - it doesn't affect your TV or Microwave.

 

[breezer]

this is true (but since you said "orr similar" we wont mention the colour of core changes)

 

[ban-all-sheds]

Phase (also known as Live)

Or Neutral.

 

[ban-all-sheds]

Result is RCD trips and turns off all power... leaving you staggering about in the dark falling over nasty sharp things and falling through those missing floorboards.....

....and thus provides a graphic illustration of why your lights should not be on an RCD.

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