new house electrics

[JohnW2]

(apologies for false start above - I realised that the light would be on in that situation, so that it would be obvious that vthe circuit wasn't dead!!)

Not only that. Even without disconnecting anything, there could be a live conductor at one of the switches on the 'switched off' circuit - which would be a hazard (L-E shock) whether or not the neutral were disconnected.

... i don't agree with that. ... The neutral supply to the isolated circuit has to be disconnected.

It's your prerogative to not agree, but before you take up BAS's suggestion and try the experiment, you might want to consdier this one possibility - and follow the red line from the supply L through Andy's body to earth (without any neutrals disconnected) ... EDIT: SEE CORRECTED VERSION ON PAGE 5

Kind Regards, John

 

[AndyPRK]

I don't seem to be able to delete this, but I'm going to replace it soon with a more pertinent diagram!

That's for the diagram John. It's a rather obvious example though John!

People would suspect the landing light was feed from downstairs.

My example was more complicated and surprising.

 

[JohnW2]

I don't seem to be able to delete this, but I'm going to replace it soon with a more pertinent diagram!

That's for the diagram John. It's a rather obvious example though John! People would suspect the landing light was feed from downstairs.

As I said in my subsequent post, they wouldn't have a need to 'suspect' with that diagram - the light would have been on!! However, in the second diagram, the light would be off, so they (particularly non-electricians) would be less likely to 'suspect! I'm sure that many people (particularly non-electricians) would assume that a light which was upstairs was on the "upstairs lighting circuit" (or vice versa). ... and don't forget that when you say that it is "fed from downstairs", that's only true of the L - the neutral is "fed from upstairs" (which makes me realise that my diagram is still wrong - watch this space )

My example was more complicated and surprising.

It was - but, as I said, one doesn't need a complicated scenario (involving disconnected neutrals) for their to be a potential hazard, at least for some people.

Kind Regards, John

 

[AndyPRK]

Even the most basic of DIY people would either:

1) Leave the landing light on, before turning the MCB off, to make sure it had gone off before starting work on a switch which controls that light.

2) Rocked the switch on and off to ensure the light didn't come on, before starting work on the switch

 

[JohnW2]

Third time lucky, I wonder?
EDIT: Third time wasn't lucky!!! PLEASE SEE CORRECTED VERSION ON PAGE 5

Kind Regards, John

 

[JohnW2]

Even the most basic of DIY people would either: 1) Leave the landing light on, before turning the MCB off, to make sure it had gone off before starting work on a switch which controls that light. 2) Rocked the switch on and off to ensure the light didn't come on, before starting work on the switch

One might hope that they would, but ..... !! When one sees and hears what some people do, I really think one has to "assume that nothing can be assumed", particularly where safety is concerned.

Whatever, the fact remains that the regs do not allow non-independent circuits (as, I hope, correctly drawn in my third attempt at the diagram!) - i.e. a light which gets its L from one circuit and its N from a different circuit.

Kind Regards, John

 

[AndyPRK]

 

[ban-all-sheds]

I don't seem to be able to delete this, but I'm going to replace it soon with a more pertinent diagram!

No - that's not the problem - that would bite you if everything were on the same MCB. And if Fingers 1 & 2 are on hands 1 & 2, possibly kill you.

Edited to add quote because yet again I simply replied to a post when there were subsequent ones. Either I've got EOA, or there's something about the new forum which invites that...

 

[ban-all-sheds]

That's it.

 

[JohnW2]

I don't seem to be able to delete this, but I'm going to replace it soon with a more pertinent diagram!

No - that's not the problem - that would bite you if everything were on the same MCB.

How? If they were both on the same MCB and it was turned off to do work, neither of the lighting circuits would be getting an L feed - so how could one get bitten?

Kind Regards, John

 

[ban-all-sheds]

How? If they were both on the same MCB and it was turned off to do work, neither of the lighting circuits would be getting an L feed - so how could one get bitten?

In your diagram they are not both off. The downstairs one is on, and is supplying, inter alia, Andy's Finger No. 1.

 

[ericmark]

The switches are the wrong way around this is the diagram we are talking about. X1 is the two way lamp and is shown here being lit from the wrong overload. I love Multisim I can actually see the lights working. As already stated the borrowing of a live means cables become live which one expect to be dead. If both switches are operated then it swaps overload so using the standard method of switching on the lights and operating an overload until they go out will not isolate the lights as if both switches are operated then it swaps overload.

Switch J2 and lamp X2 are just to show how the supply gets to the switch.

Here shown powered from the other overload.

 

[JohnW2]

How? If they were both on the same MCB and it was turned off to do work, neither of the lighting circuits would be getting an L feed - so how could one get bitten?

In your diagram they are not both off. The downstairs one is on, and is supplying, inter alia, Andy's Finger No. 1.

You were talking about a situation in which both circuits wre supplied by the same MCB - in that case there wouldn't be a 'both' - the (one) "lighting MCB" would be either on or off - and hopefully 'off' if anyone was working on any part of any of the lighting system(s)!

Kind Regards, John

 

[ban-all-sheds]

No - the situation I was talking about was where there are 2 MCBs, one for the upstairs lights and one for the down. In your diagram poor Andy gets a DIY cardioversion no matter how the neutrals are arranged.

 

[AndyPRK]

Surly no one uses that system in the UK Eric! As when both switches are up, the circuit protection is shorted together and its effectiveness reduced.