Flickering Light Has Finally Died

The main lights in the living and dinning room are controlled by a swtich panel with two separate dimmer switches. The one controlling the living room light works fine, but the one for the dinning room used to flicker and go quite dim until it was practically off. Now it's stopped working altogether.

Could anyone suggest a cause? I'm going to try changing the switch but is this likely to fix the problem or does it sound like something else?

what kind of lights are theese?

ordinary bulbs?
mains halogens?
low voltage halogens?
something else?

It sounds like you have a dirty pot track in that dimmer. Why not swap the two dimmer switches over and see what happens. If the dining room lights work but the living room ones don't that settles it. New dimmer required.

WARNING: DON'T GET YOUR WIRES MIXED UP!!!

Thanks, I'll try that.

They're just ordinary, plain, boring 100 W bulbs.

Also, whilst I'm on the topic of light switches and wires; I recently changed the pull switch in the bathroom and noticed that the black wire was unused. In the old switch, two red wires went to opposite ends and the black wires were wrapped around each other an unused (same for the earth).
I've wired the new switch up the same as the old one except for the earth which I've wired in to the appropriate place. I don't see what it's for though, since the bit it [earth wire] screws into seems isolated.

Thanks for your help.

sounds like your bathroom light is wired something like this



nothing wrong with this wiring arrangement but wires should not be joined by twisting. chock block should be used.

username#132 said:

Also, whilst I'm on the topic of light switches and wires; I recently changed the pull switch in the bathroom and noticed that the black wire was unused.

Click to expand...

Possibly not unused - just not switched. If you undo the join between the two blacks does the light stop working?

the earth which I've wired in to the appropriate place. I don't see what it's for though, since the bit it [earth wire] screws into seems isolated.

Click to expand...

It is, but the cable always has an earth wire in it, and it has to go somewhere, and if you ever put a metal switch in it will be needed....

Yeah, thanks to you both - I'm pretty sure I understand the configuration now!

As for the dinning room dimmer switch, I had to make a sketch and put it straight back because I didn't have a clue...

Picture

Picture added - see above

Looks like, live comes in on one red, and is split into the 2 switches, each at terminal number 3 (call them 3a and 3b) in your drawing, and then 2 switched lives (terminals 1a and 1b) go back, one to each lamp, one through a black (or was that brown?) and the other through the non-supply red. If you swap over the black with the red that is not the split red, the two lights wil have changed sides.
If the dimmer is defective the fault will have stayed with the switch, so now the other lamp will have the problem. If the fault is after the dimmer, the fault will still be at the same end of the room, but the dimmer switches will have changed sides, and you can clear the other dimmer from guilt.
As you are not sounding too confident I recommend a marking of the red wires, and possibly name the 2 gangs of the switch with tippex or indelible pen, so you can get back to the original condition (" I'd like to help you out - where did you come in?") and also sketch it out on a notepad as you go along, so you can remember the results afterwards.

I understand, yeah, I feel kinda stupid for no being able to figure that out myself. I don't know the difference between live and switched live (is switched live the same as neutral) though.

I never really understood how alternative current worked... i figure it goes back and forth along the same wire which I figure is what is happening on electricity pilons. In this case, all electrons at any point in the cables (assuming this point is the same distance from the substation for all cables), the electrons are all going in the same direction at the same speed at the same time.. is that right? So there is only a live on pilons, and no "neutral" or "switched live"?

In this case, where does the neutral come from? Is it connected to earth?


Anyway, I've already got labels written on scotch tape although I think I'll be okay just swapping those two wires.

What do you mean by "where did you come in"??

The Live is from the supply, and is live regardless of switch position (and alternates between plus and minus 330 Volts or so, 50 times a second and averaged over time has a heating power equivalent to about 230 or 240 volts DC. That is the significance of the 230V RMS rating.)
Neutral is the other terminal of the generator, and stays at around zero volts, being earthed at the substation transformer, and possibly other places too, but let's not worry about that just yet. So on negative half cycles electrons are rushing out of the live towards either gound or neutral, we prefer neutral, as if they go by any other route, something has likely gone wrong. On the positive cyycles they try and get back. So you may think of the live as alternately sucking and blowing to make the the electrons trot back and forth in the wire.
Now both adding and removing electrons hurt just as much, only the direction (current sense) has been reversed, but both an entry and an exit burn hurt equally, so us being earthed and touching live is a bad thing.
The switched live is connected to live when the switch is in the on position (or part-time connected if the dimmer is half way up the brightness scale -dimmers slice up te waveform, but the eye, and the heating/cooling inertia of the filaments conspire to smooth over the flicker.)
If the switch is off the switched live wire, the one from switch out to the lamp is dead (isolated from live), and no current flows.
Neutral, at least in this circuit, does not come to the switch at all, but goes straight to the light fitting by route as yet unknown. If swapping the wires does not move the flicker from one lamp to the other, then working out how the neutral wiring gets to the lamp (or rather how the current gets back from the lamps non-live side to the supply neutral, to keep the picture simple) is your next task, though removing the light fitting and having a look behind it is always a good start.
Flickers often mean loose screws or dirty or corroded wire not making a good shiny metal to metal contact with good contact force. Often just to dismantle clean, polish and refit is enough to restore operation, if you can find which is the poor joint.

PS
"i'd like to help you out ! -How did you come in?" is a line from a comedy show, but I can't remember which one. I was referring to the fact that my idea of help may not always be so useful -its hard to get the technical level right with someone you don't know -mark it down to my funny humour

I see. You seem to have the technical level about right. I did A level physics a couple of years ago so I have a theoretical idea of electricity but applying it to practical situations is something else. We never actually discussed the idea of 'neutral'.

What I don't understand now is why you would connect one terminal of the generator to earth since that seems like a waste of energy? Why can't this terminal be used to provide electricity just like the other? I figure the flow of electrons from both terminals are in antiphase but what does it matter if someone in Liverpool has a lamp whose electrons are going from left to right whilst someone else in Manchester has the same lamp with electrons going the other way?

If you wanted a zero volt connection, surely you could just use Earth and not waste the other terminal?



Also, the fault would appear to be down to the dimmer switch. We've bought a normal flick switch instead, since mum never really uses the main lights and when I do I want it on full.
Thanks for the dimmer switch explanation - I always thought it was just a variable resistor but what you described sounds like a much better idea!!


I know I must be killing you with all these questions, but you know the way electricity demand fluctuates? If the generator(s) continues at the same rate, what happens to the 'spare' energy, people aren't using?

Well, really neutral is earth - and you can supply power with just two wires - in fact its the modern way (AKA PME) The second wire is split into an earth and a neutral at the house. The other reason for grounded neutrals is 3 phase -try wikipedia, it has nice pictures.
Or here, but its a bit heavier...
http://www.mikeholt.com/documents/mojofiles/electricalearthingworldwide.pdf
The question of which conductor is constant voltage and which is changing is purely an issue of convention. You could say the live conductor is at a fixed voltage and the rest of the world is changing voltage with respect to it, this is certainly how it looks to electrons in the live wire - that's what makes them so keen to get on and off it on alternate half cycles. The available energy depends only on the difference in voltage between the terminals, which in turn depends how fast it is the generator is rotating, and the B field through the windings.
In a well organised system no current flow down the earth wires, except for a small leakage though capacitance, and any large current indicates a fault - and detecting this is happening (by comparing live and neutral currents) may save a life.

As regard electricity demand, as the load current in the generator windings falls, the torque required to turn the generator at constant speed also falls, so the steam pressure on the turbines can be relaxed for the same speed, and so the amount of coal, oil or gas burnt also falls. Also in the idle periods economy 7 control switches are switched on and off by phase modulation of the radio 4 long wave carrier, allowing a degree of load balancing. (at least in the newer installations - as I'm reminded, some use clocks still)
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