John P
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| posted on 19/10/12 at 01:04 PM |
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Help with Home Electrics Needed!
In the days of fuses you could isolate a circuit by removing the appropriate fuse and then work on this even though all the other electrics in the
house were still in use.
Yesterday I was putting up a new light fitting in a room which has virtually no natural light so I isolated the lighting circuit by tripping its MCB
and then plugged a lead light into a convenient socket outlet so I could see.
Whilst working however I obviously touched the neutral onto the earth wire which immediately tripped the RCD on the consumer unit plunging me into
darkness.
I believe this is because even though I had tripped the MCB on the circuit I was working on the neutrals and earths are still connected in the
consumer unit so touching neutral to earth causes enough current to flow to trip the RCD.
Is there a safe way to avoid this happening as I ended up having to do the work by torch light which was both difficult for me and also meant all the
electrics in the rest of the house were out until I had finished.
John.
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mookaloid
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| posted on 19/10/12 at 01:31 PM |
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you need one of these
"That thing you're thinking - it wont be that."
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daviep
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| posted on 19/10/12 at 02:11 PM |
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If shortening a cable don't cut all the wires at the same time and then stick a bit of tape around the neutral, or that's what I do 
No idea what the correct procedure is so I'll be following with interest.
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
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Not Anumber
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| posted on 19/10/12 at 02:19 PM |
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It depends on the consumer unit. Some are setup as split units with a bank of circuits switched/protected by an RCD and a seperate master swich for
other circuits. If yours is like this then it's best to connect your lead lamp to a non RCD circuit. Many consumer units are modular
construction once you get the cover off so you can bolt in an extra master swich and shuffle the MCBs to make it a split unit.
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lsdweb
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| posted on 19/10/12 at 04:58 PM |
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Remember that the neutral is actually 'live'!
Safest way is to isolate all. Alternatively, disconnect the neutral(s) for that particular circuit from the Busbar in the unit.
W
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daviep
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| posted on 19/10/12 at 05:07 PM |
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quote:
Originally posted by lsdweb
Remember that the neutral is actually 'live'!
W
Can you explain this to me please?
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
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whitestu
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| posted on 19/10/12 at 05:37 PM |
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Given the nature of alternating current both N and L are effectively live. An MCB for a single circuit only cuts the phase conductor [line in the
diagram] so there is still a path from the neutral back to the supply.
[img]
 
Description
[/img]
If you shut off the main breaker on the distribution board this cuts both as it is a double pole switch.
Stu
[Edited on 19/10/12 by whitestu]
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slingshot2000
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| posted on 19/10/12 at 06:15 PM |
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quote:
Originally posted by daviep
quote:
Originally posted by lsdweb
Remember that the neutral is actually 'live'!
W
Can you explain this to me please?
Cheers
Davie
It is AC ! The Live is there, just trying to alternate across the Neutral. Isolate means breaking both Phase (live) and Neutral. Switching off, by; a
switch, MCB or removing fuse; does only disconect the Phase ! You would have to be very unlucky, but it is possible to get a dangerous feed back along
the Neutral path.
If in DOUBT switch the whole fuse - box / consumer - unit /distribution - board OFF !
YOU CANNOT SEE IT, AND IT CAN KILL YOU !
Regards
Jon
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daviep
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| posted on 19/10/12 at 06:37 PM |
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quote:
Originally posted by whitestu
Given the nature of alternating current both N and L are effectively live. An MCB for a single circuit only cuts the phase conductor [line in the
diagram] so there is still a path from the neutral back to the supply.
[img]
Description
[/img]
If you shut off the main breaker on the distribution board this cuts both as it is a double pole switch.
Stu
[Edited on 19/10/12 by whitestu]
That still doesn't explain it to me, if you take a meter and check neutral to earth you get 0 volts, in fact the picture clearly shows that
neautral is connected to earth at the generator.
The picture is demonstrating how it's possible to get 415v shock from house hold sockets if they are on different phases of the supply, for
example using an extension cord to the house next door which may be on a differnt phase.
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
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slingshot2000
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| posted on 19/10/12 at 06:51 PM |
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Davie,
yes you are correct in how you are seeing the diagram, but that is not what I said or described. Unless you disconect there is always a chance
that an ALTERNATING LIVE PHASE could still be connected to the Neutral terminal. Disconect Phase and Neutral and you are safe !
The Electrical Regs actualy call both Phase and Neutral; Live Conductors! They also state that one should ;
"Never work live" !
As i stated above;
You CANNOT SEE, AND IT CAN KILL YOU !
It is your life, gamble with electricity all like !
Regards
Jon
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JoelP
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| posted on 19/10/12 at 06:57 PM |
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when other circuits in the house are in use, neutral will be a few volts above earth due to resistance in the neutral conductor back to the
substation. Imagine it being like a queue of electrons, albeit they are really heading both directions. The earth is thus a shortcut for them, and
enough current can flow to trip the RCD. The solution is to either be careful not to cut the cable in one, as the cutters will short N-E, or remove
the neutral from the busbar for the particular circuit you are working on. Also remove the live from the mcb, and you should hang a warning sign on it
to reduce the chance of someone messing with it whilst you are working. I've had tossers turn the power back on whilst im working so i dont take
any chances now.
Neutral is indeed classed as a live conductor these days, it was decided that if you only called brown live then it makes people assume neutral is
always harmless - both are live, one is called phase, the other neural. Earth is really called the cpc, for circuit protective conductor.
Neutral is indeed usually harmless, but it pays to remember that it is an unbroken line back to the substation where big volts are present, and in a
fault you never know whats going to happen.
[Edited on 19/10/12 by JoelP]
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slingshot2000
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| posted on 19/10/12 at 07:23 PM |
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quote:
Originally posted by JoelP
when other circuits in the house are in use, neutral will be a few volts above earth due to resistance in the neutral conductor back to the
substation. Imagine it being like a queue of electrons, albeit they are really heading both directions. The earth is thus a shortcut for them, and
enough current can flow to trip the RCD. The solution is to either be careful not to cut the cable in one, as the cutters will short N-E, or remove
the neutral from the busbar for the particular circuit you are working on. Also remove the live from the mcb, and you should hang a warning sign on it
to reduce the chance of someone messing with it whilst you are working. I've had tossers turn the power back on whilst im working so i dont take
any chances now.
Neutral is indeed classed as a live conductor these days, it was decided that if you only called brown live then it makes people assume neutral is
always harmless - both are live, one is called phase, the other neural. Earth is really called the cpc, for circuit protective conductor.
Neutral is indeed usually harmless, but it pays to remember that it is an unbroken line back to the substation where big volts are present, and in a
fault you never know whats going to happen.
[Edited on 19/10/12 by JoelP]
I think we seem to be quoting from the same song - sheet here, Joel. I too have seen some one get a NASTY belt from someone else's stupidity!
Now I try to minimise any risk to my safety and if in doubt either lock OFF or get someone I trust to watch my back !
As before;
Regards
Jon
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