Is lightswitch in the Live or the Neutral wire?

[treez]

In a UK/European/USA domestic home, is the actual switch in a wall light-switch in the Live or the Neutral wire, or both?

 

[Dan Mills]

In the UK it is normally in the phase conductor, and in fact there may not be a neutral at the switch, but this is not to be relied upon and both phase and neutral are to be considered live wires for the purposes of insulation and protection from accidental contact.

HTH.

Regards, Dan.

 

[treez]

Thanks Dan.
Just out of interest, if Neutral is touched....then it shouldn't give a shock?
I mean, Neutral is always connected to Earth somewhere back in the supply system?
You would think it would be safer to put the switch in the neutral?

 

[Dan Mills]

If you put the switch in the neutral then the lamp socket contacts are live even when the switch is off, I am not seeing much safety improvement there.

While theoretically the neutral should be close to earth, this is not a safe assumption (A broken neutral can put the neutral wiring up to 230V above ground depending on the relative phase loading) so both the phase and neutral conductors are treated as live for the purpose of insulation and protection from contact, normally only the phase conductor has overcurrent protection however.

Regards, Dan.

 

[ftsolutions]

Plus, if you have a single light that is wired to be operated by 2 or more switches, what you might "think" is neutral at the light might not be. White neutral wires are to be coated black, or a third wire color is to be used for multi-way light switching of single phase AC if switching of line voltage is to occur on multiple wires, as in a 3-way switch scheme. I'd strongly suggest that you get an AC wiring handbook.

 

[Disha Karnataki]

If you put the switch in the neutral then the lamp socket contacts are live even when the switch is off, I am not seeing much safety improvement there.

how?? could u elaborate

 

[betwixt]

Disha Karnataki, consider what happens if more than one lamp is wired in parallel, for example two ceiling lights on one switch. If the neutral is broken by the switch, the phase (live) wire is still connected directly to one side of the lamp socket and via the low resistance of the other lamp to the other side of the socket. In a correctly wired system, and under no-fault conditions, the neutral voltage is very low compared to the phase so is considered much safer.

Treez, the conventional way of wiring lighting in the UK is to run a permanently live phase and neutral from one fitting to the next. From the fitting there is a twin wire & Earth to the wall switch which is a live feed and live return. The neutral side is always connected in the fitting. The need to link incoming live and the feed to the switch is why there is always a terminal block inside them. In a change over (dual switch) situation, an extra wire is used whch links the two switches to make a crude XOR logic system.

Brian.

 

[Disha Karnataki]

Disha Karnataki, consider what happens if more than one lamp is wired in parallel, for example two ceiling lights on one switch. If the neutral is broken by the switch, the phase (live) wire is still connected directly to one side of the lamp socket and via the low resistance of the other lamp to the other side of the socket.
Brian.

omg what is this i am at a fix now i got your point why we are placing switch in the line conductor but,..
Now my 50% doubt is cleared about why should the switch be placed along the line. I am still not getting why did dan mills said that:
"""If you put the switch in the neutral then the lamp socket contacts are live even when the switch is off""" i didnot get this point...

 

[FvM]

Connection of a single-pole switch to live wire will be usually required by national regulations (respectively disconnection of neutral by a single-pole switch interdicted), e.g. DIN VDE 0100-460 in Germany. I presume there's a similar UK standard.

Nevertheless, the rule should be considered only as a supplemental safety measure, nothing you can rely on when e.g. touching an electrical circuit.

 

[Dan Mills]

Indeed.

With a switch in the neutral, there will be one terminal of the light socket that is permanently live with respect to earth, and most shocks are to earth rather then across the contacts, so switching the live can give a little extra safety for all that it must not be relied upon.

Regards, Dan.

 

[FANT]

It is mandatory that the command switch is connected to the live wire instead the neutral.
This is to protect the user from electric shock when you are working on the lamp, i.e. changng it.
In Italy this is ruled by the 64-8 technical rule, that is given from an IEC rule.

So I think this is the same for all the world.

Mandi

 

[FvM]

In Italy this is ruled by the 64-8 technical rule, that is given from an IEC rule.

So I think this is the same for all the world.

Yes, you are right, should be covered by IEC 60364-4-46.

IEC 60364-4-46: Electrical installations of buildings – Part 4: Protection for safety – Chapter 46: Isolation and switches