Two red wires causing confusion

[BriSCABoy]

Hello

I want to replace some dimmer switches with conventional on/off switches, but it's old wiring which is confusing.

The dimmer switch has two red wires connected, one to L1 and the other to L2. There are no distinguishing marks or sleeves on the wires to indicate which is Live and Switched Live.

The conventional light switch I want to use has L1, L2 and COM.

How do I correctly connect the wires to the new switch?

Does L1 go to L1 and L2 to COM, or vice versa?

Cheers

Jason

 

[Taylortwocities]

I guess you dimmer only has two terminals ( L1 and L2?)
If so, Just put one wire on COM and the other on L1 on the new switch, it doesnt matter much which way round they go.

Strictly speaking the permananet live should go on COM, but you would need a multimeter to test which red that might be.

 

[winston1]

Strictly speaking the permananet live should go on COM

Why?

 

[JohnW2]

Strictly speaking the permananet live should go on COM

Why?

Functionally, it obviously doesn't make any difference. However, there appears to be a convention, the basis for which | don't fully understand (In fact, I think I could probably put forward an argument for the opposite!) that when using a switch, relay contacts or whatever for switching, the 'live feed' should go to the moving contact, and the load to the fixed one.

Kind Regards, John

 

[BriSCABoy]

I guess you dimmer only has two terminals ( L1 and L2?)
If so, Just put one wire on COM and the other on L1 on the new switch, it doesnt matter much which way round they go.

Strictly speaking the permananet live should go on COM, but you would need a multimeter to test which red that might be.

Thanks for answering.

There is a 3rd terminal on the dimmer but no wires connect to it.

Kind Regards

Jason

 

[Taylortwocities]

The switch that the OP has is a changeover switch. The convention for ℅ switches is the feed goes to the centre contact and then you can select the output that you require (NO or NC contact).

I now wish I hadn't even mentioned it. I only did add that bit because if I had not, some smart @rse would have come on to say that the feed should be on the COM (as is usual). Now I have another smart @rse asking why I gave that guidance.

Maybe I should do what some people do: just sit there looking, not giving any real help, but just sniping at any information that is posted.

 

[JohnW2]

The switch that the OP has is a changeover switch. The convention for ℅ switches is the feed goes to the centre contact and then you can select the output that you require (NO or NC contact).

Indeed - and, as I tried to explain to winston, an extension of that convention seemingly applies even to "1-way" ("on/off") switches, such that the feed should go to the moving contact (even though I could probably argue that it was fractionally 'safer' the other way around!).

I now wish I hadn't even mentioned it. I only did add that bit because if I had not, some smart @rse would have come on to say that the feed should be on the COM (as is usual). Now I have another smart @rse asking why I gave that guidance. ... Maybe I should do what some people do: just sit there looking, not giving any real help, but just sniping at any information that is posted.

You could do that, but I don't think it would really be in your nature so to do. We are all repeatedly faced with the "can't win" situation you describe in relation to what we do and don't write here. One of the reasons why my posts are often lengthy is that I have learned from bitter experience (here and elsewhere) that if I don't mention all details, and consider all possibilities, in my initial response, one of those to whom you refer will probably take me to task for my 'omission' - so, like you did, I usually try to pre-empt them!

Kind Regards, John

 

[EFLImpudence]

Why would the switched output be called Common?

 

[BriSCABoy]

The switch that the OP has is a changeover switch. The convention for ℅ switches is the feed goes to the centre contact and then you can select the output that you require (NO or NC contact).

I now wish I hadn't even mentioned it. I only did add that bit because if I had not, some smart @rse would have come on to say that the feed should be on the COM (as is usual). Now I have another smart @rse asking why I gave that guidance.

Maybe I should do what some people do: just sit there looking, not giving any real help, but just sniping at any information that is posted.

Erm...unsure if this was aimed at me, but I was happy with your original response and plan on replacing my dimmer switches using the advice you have given.

Thanks once again

Kind Regards

Jason

 

[EFLImpudence]

.unsure if this was aimed at me

No, it wasn't.

 

[Taylortwocities]

Why would the switched output be called Common?

An input that is COMMON to the two outputs, perhaps.

And BriSCABoy, no the comments was cdertainly not directed at you.
More at a 1984 person.

 

[EFLImpudence]

Why would the switched output be called Common?

An input that is COMMON to the two outputs, perhaps.

Yes, that was my point. I agree with you.

 

[JohnW2]

Why would the switched output be called Common?

An input that is COMMON to the two outputs, perhaps.

Yes, that was my point. I agree with you.

Whilst, as I've said, I agree about what the conventions are, the above, in itself, is not a universal explanation as to which are 'inputs' and which are 'outputs'. It is common in electronics, and far from unknown in 'electrics' (e.g. with a generator/grid supply c/o switch) for one output to be COMMON to two inputs.

Kind Regards, John

 

[bernardgreen]

The convention for ℅ switches is the feed goes to the centre contact and then you can select the output that you require (NO or NC contact).

If using a change over switch for a simple ON-OFF switch then taking the Switched Live from COM and feeding Live into L1 ( or L2 ) has the advantage that the un-used terminal is never Live.

 

[ban-all-sheds]

Of course all of this could have been avoided by Plan B:

Realising that if the switch works OK now it must be wired correctly, actually learning about and coming to genuinely understand what switches do, and thus knowing how to transfer the wires from the old switch to the new rather than being in a position of fiddling with things without understanding them.