2 way switching

[supercal]

I was cleaning some paint off a 3 gang switch recently. Switch wasn't going back easily, so I disconnected one wire. At least I think it was only one wire. But I messed up: now the landing light and sitting room light will only come on when hall light is on.

I'm not happy to try experimenting with mains electrickery. Just to explain my background: experienced electronics engineer who has done some wiring under an electrician's guidance in the past.

I believe I can draw a basic diagram on paper of what is happening, but cannot figure out how moving the one wire caused this switch to work in series.

A picture might help.

The 2 wires on bottom left are for 2 way switch of landing light. Top wires are wired as common. Middle switch must be on for others to work.

Now knowing the previous house owner was some sort of technician and from other links I've followed from here, I suspect there might be a short cut made inside this switch wrt the common.

Can anyone help me?
TIA

 

[plugwash]

the most likely explanation is that you swapped the permanent live with the outgoing live for the middle switch

do you own a multimeter?

 

[pdcelec]

Just wondering what subject electronics engineers learn these days. I always thought it was electrically biased?

 

[ban-all-sheds]

Try swapping the wires from the wall that go into the two COMs - i.e. top-right & bottom-centre in the photo.

 

[mapj1]

what the photo shows is a standard 3 gand 2 way switch.
If we call them ABC from left to right, they are mounted "696" to space the terminals easily.

Com is the slider, and so for example A comm goes to A1 with the switch up, and A2 with the switch rocker down (or the other way around)
I suggest you try and reconcile what you have with the 'for reference' drawings of diferent types of 2 way switching - there are at least 3 flavours in common use. and then draw it out.
The switch where command only one terminal is in use is being used as a simple switch.

The link between A and B gangs will be steady live, and saves on duplicated switch drops.

 

[supercal]

Thanks plugwash, ban-all-sheds and mapj1 for the useful comments. Swapping top-right and bottom middle did the trick. New multi-meter bought. Haven't had to use one for years.

@pdcelec: back in the day I did my degree, we specialised in electronics, which means physics, some chemistry, systems, computing. Didn't learn heavy electrics, bridge building, gas turbines. What sort of stuff did you do?

 

[mapj1]

I don't know what PDelec did, but I know what used to be taught not so many years ago when I was on the research staff of a moderately well known university department... before I sold out and went for a real job - now I do it for a living .

In no special order, and probably missing out loads of stuff my former colleagues would kick me for not mentioning as it was their private speciality...

DC circuits
AC circuits
Fields and waves, from magnets, bulbs, and batteries to Maxwell's equations.
Control systems, feedback loops, stability and instability
Transistors and op-amps.
RF and microwave
Solid state theory.
Vacuum electronics, including cold kathode emission.
Mathematics to cover all the above.
Some microcontroller stuff,
Options in higher levels of some of the above, and related things like programming in C, while not per-se electronics, are still popular course modules, and electronics for instrumentation, biology EMC testing lasers and optics etc. Business and manegement options, always poular with the students you could see were not going to use the electronics for work, as fewer sums involved of course.
While heavy electrics like ward leaonard motor controllors and Buchholz Relays may be be a bit deep, I'd expect the solution to the light switch problem to be covered by the rules of kirchoffs laws in the first 2,
I'd agree if you don't use the knowledge, it is suprising what one can forget, and with mains, confidence is important - there are 3 outcomes, it works, nothing and, "oh dear". You need to be reasonably confident of which before switching power back on !
best regards M.

 

[jtaunton]

To be fair, even with an understanding of circuit theory, someone who spends their day down at 5V could easily get the willies at the idea of experimenting with 240V........

 

[ChrisR]

kirchoffs laws?? No way!
Light on = A & B OR (Not A & Not B)

Simple bit of logic!

When I did it there was a lot more about radio transmission, control theory, laplace transforms, ugh!

Did a spell with power transmission guys - anything less than 2 amps is Leakage!

 

[pdcelec]

Thanks plugwash, ban-all-sheds and mapj1 for the useful comments. Swapping top-right and bottom middle did the trick. New multi-meter bought. Haven't had to use one for years.

@pdcelec: back in the day I did my degree, we specialised in electronics, which means physics, some chemistry, systems, computing. Didn't learn heavy electrics, bridge building, gas turbines. What sort of stuff did you do?

When I did my HNC in electrical and electronic engineering, we learnt about electrical and electronic stuff including physics, chemistry, systems, computing, but we also learnt about circuitry and how it worked. I too did not learn bridge building, gas turbines etc. For this type of work though, I found that the C+G 2360 and 2391 are much more relevant.

 

[ban-all-sheds]

One thing still puzzles me...

Switch wasn't going back easily, so I disconnected one wire.

What was the thinking behind that?

 

[stevesey]

Thanks plugwash, ban-all-sheds and mapj1 for the useful comments. Swapping top-right and bottom middle did the trick. New multi-meter bought. Haven't had to use one for years.

@pdcelec: back in the day I did my degree, we specialised in electronics, which means physics, some chemistry, systems, computing. Didn't learn heavy electrics, bridge building, gas turbines. What sort of stuff did you do?

When I did my HNC in electrical and electronic engineering, we learnt about electrical and electronic stuff including physics, chemistry, systems, computing, but we also learnt about circuitry and how it worked. I too did not learn bridge building, gas turbines etc. For this type of work though, I found that the C+G 2360 and 2391 are much more relevant.

Shows the difference between electric and electronics engineering courses and just electonic engineering courses. I did the former so we did lots of AC/DC motors, 3 phase stuff, control systems, maxwells equations and the like (no bridges and gas turbines though - that's for the mechanical types).

 

[ban-all-sheds]

And here's me, with none of that, and all I did was draw a sketch of what went to each switch terminal and saw what must be wrong.

Sometimes the simple solutions are the best

 

[pdcelec]

Exactly the reason for my first post. Switch wires aint rocket science.

 

[mapj1]

I really wish people wouldn't use 'Rocket Science' as an example of something difficult. It is remarkably deterministic compared with, for example organic chemistry (ask Mr Markov) or even deducing a nuclear decay sequence (liquid drop model anyone?). Remember folks,
rocket science isn't really Rocket Science.
Ah.
damn.


regards M.
PS though as B_A_S has pointed out, it's not the formal qualifications that count, its the understanding required to make the deductions, and the confidence to follow it through. Experience comes into it too of course.

PS2 no one expects the spanish inquisistion..