Domestic Electrics Circuits

Thread Starter

dai_b

Joined Dec 13, 2016
2
I used to be an electrician many many many years ago, and seem to have forgotten some fundamentals, any help would be greatly appreciated.

I am simply replacing a double socket front, and extending the cable a little to move a few inches. Downstairs.

I have switched the Circuit Breaker to the downstairs sockets to open/off

When I snipped the cable behind the old socket, my snips obviously went through Live Neutral & Earth together, and it caued the MCB to trip.

If the circuit has been isolated by the "downstairs Sockets" Circuit Breaker, how is this possible please?
 

AlbertHall

Joined Jun 4, 2014
11,217
Because that circuit wasn't isolated by that breaker.
I am not an electrician and I always check that a circuit is isolated before working on it - neon screwdriver or similar.
 

Thread Starter

dai_b

Joined Dec 13, 2016
2
Because that circuit wasn't isolated by that breaker.
I am not an electrician and I always check that a circuit is isolated before working on it - neon screwdriver or similar.

Hey, I have a proper voltage tester and it shows no voltage, just continuity.
 
This is where what part of the world your in would help.

"It" and "continuity" makes no sense.

"continuity" between E and N makes sense. etc. 1 ohm between E and N makes sense.

If a light bulb was it. "It" would have continuity.
 

AlbertHall

Joined Jun 4, 2014
11,217
Is the circuit breaker single or double pole?
Is the MCB solely for this circuit or for the whole house?
Is the MCB only an overcurrent breaker or is it an RCD/ELCB?
 

blocco a spirale

Joined Jun 18, 2008
1,546
The breakers in consumer units usually only isolate the Line (they are for overload protection rather than isolation) so I think it is still possible to trip an RCD if Neutral is shorted to Earth and enough current flows due to it not being at quite the same potential. Before starting work you should isolate at the main circuit-breaker as this should also disconnect the Neutral.

And, I wouldn't have cut through all three conductors at the same time unless I was absolutely certain the cable was isolated.
 
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tcmtech

Joined Nov 4, 2013
2,867
I have switched the Circuit Breaker to the downstairs sockets to open/off

When I snipped the cable behind the old socket, my snips obviously went through Live Neutral & Earth together, and it caued the MCB to trip.

If the circuit has been isolated by the "downstairs Sockets" Circuit Breaker, how is this possible please?
Obviously the line you cut into was not the circuit you turned off.

Mislabeled panel or incorrectly assumed locations of related wiring for that circuit is the problem I see.

The old house I grew up in had no rational or reason to the wiring layout. One circuit breaker controlled one bedroom, bathroom and part of another room yet the bedroom right next to it had three different circuits feeding the three outlets and light and one of those circuits ended in another room at the far end of the house in just one odd outlet at the farthest point in the room. :confused:
 

tcmtech

Joined Nov 4, 2013
2,867
it must have been a very very very long time since he worked as an electrician and has since completely forgotten the basics
Have you worked with any typical electrician and electrical contractors lately? Not too many well lit bulbs in their buildings I can say that much. :oops:

Pull out a up to date code book on one while they are working some time. The first response you are going to get is likely going to be you getting questioned about what inspection agency you are from and if you aren't an inspector they don't have to answer any of your questions regarding anything the code books says. :(

To me that's like walking into church with a bible and opening up to a page and asking the preacher what something means then getting told to go screw yourself since you're not from a higher level of the church they are required to answer to. :rolleyes:
 

blocco a spirale

Joined Jun 18, 2008
1,546
Have you worked with any typical electrician and electrical contractors lately? Not too many well lit bulbs in their buildings I can say that much. :oops:

Pull out a up to date code book on one while they are working some time. The first response you are going to get is likely going to be you getting questioned about what inspection agency you are from and if you aren't an inspector they don't have to answer any of your questions regarding anything the code books says. :(

To me that's like walking into church with a bible and opening up to a page and asking the preacher what something means then getting told to go screw yourself since you're not from a higher level of the church they are required to answer to. :rolleyes:
It's common in lots of semi-technical vocations where people have learned primarily on the job. They believe they have knowledge because they have years of experience in doing whatever it is they do but they lack in-depth understanding and when asked a question that requires them to apply some understanding they find all sorts of ways to avoid the embarrassment of saying they don't know. These people are easy to identify because they often start sentences with the words "I was always taught....."; four words that anyone who understands their subject would never use.

I have more respect for anyone who says they don't know because at least it's honest and we all know where we stand.
 
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