Dimmer switch just went again for the second time in a few months that we’ve been renting this flat. Snap, crackle and pop from behind the switch with blue arc light. Replaced the first time, this reply from LL when I told him about the second time.

“Electrician will call you. He has told me a dimmer is like a light bulb, a consumbable, and can break if a bulb goes so he will replace it this time but not again. You can either have a dimmer and if it goes again I will put in an ordinary light switch or we can put in light switch now.”

I’m no electrician, but this doesn’t sound right to me. I think it’s more likely that the wiring’s dodgy, leading to overloading of the switch.

As I said though, I’m very much not an electrician.

Any thoughts?

Ta!

Sounds like the dimmer isn’t rated for the load, so burning out.

Dimmers are not a consumable. Get him to conduct a wiring inspection – it might be a short to earth somewhere causing that.

I had this recently – we have 6 x 50W halogens in a room and the dimmer went bang. Bloke in B&Q (I know, I know) suggested that the spike when a halogen goes could exceed the rating of the dimmer. The replacement that I’d already selected from the shelf was rated below the 6 x 50W! I changed it for a 400W rated version but said B&Q sage suggested getting eco halogen bulbs with lower ratings to maximise the chances of the dimmer surviving the next time a bulb goes pop. I have no idea if any of this is true but sounded plausible to me…

I have no idea if any of this is true but sounded plausible to me..

eco halogens might help as they are a little lower power. General eco bulbs WON’T work as they are not the right sort of load and are more likely to destroy the dimmer 🙁

Fault current will be higher than operating current. this is what the switch needs to be rated for. just sounds like badly spec’d kit.

Consumable? he’s having you over!. think of it this way, if it were consumable then the potential for wiring damage in the box is quite high (ignoring the fire risk) so at some point you would have to replace the wiring in that box! also to compare it to a light bulb is bizzare as its designed to be replace easily and relatively safely by the avereage person.

Dimmers are not consumable. Someone is telling porkies

Dimmers aren’t consumables +1

But make sure that you haven’t put any low energy bulbs on that circuit as that is likely to kill them. You need both a special dimmer and special low energy bulbs for that to work

Interesting, I am climbing off my high horse, but for now, only as far as the top of the fence. Keeping a hand on the reins for the time being.

I can’t remember whether we’ve got low energy bulbs in there or not. There were some which needed replacing when we moved in, but I think we consolidated the remaining incandescents (40W, I think) into the living room.

Given that you can’t get incandescents now, aren’t they all “low energy eco bulbs”? What are the ones called that I’d need to get to reduce the load on the dimmer? need small screw cap. And there are 5 light fittings (wall uplighters). What would those in the know be speccing for the dimmer?

If anyone can give me some specs I can pass on, that would be ace. Thanks!

I can’t remember whether we’ve got low energy bulbs in there or not.

You’ll need to go take a look then.

Given that you can’t get incandescents now, aren’t they all “low energy eco bulbs”?

I don’t know what you can get unfortunately :(. I now only use a dimmer on some halogens that I have

And there are 5 light fittings (wall uplighters). What would those in the know be speccing for the dimmer?

The ‘eco’ halogens are incandescents so should be ok. The problem is only with the low energy bulbs that look like fluorescent tubes all twisted up.

I seem to remember the dimmer I had running my kitchen halogens was rated for lower wattage of halogens than conventional bulbs.

As others have said – switches are not a consumable. Problem is either –
– overloaded switch
– crap quality switch (cheap dimmer switches don’t last long but that shouldn’t mean it’s your problem as a tenant)
– other fault in circuit.

as touched on above there are a number of dimmer/bulb compatability issues.

1) The total load of the lighting circuit needs to be in the acceptable range of the dimmer. 10x 50w halogens or incandescents is quite a bit for example. And there are a lot of 100W-300W dimmers out there…

2) Low wattage circuits can be a problem in the other direction – the dimmer cant deliver the lower level of power – i.e. a 4x25W halogen circuit cant be dimmed properly with a 200W-400W dimmer.

3) Megaman (others available) produce a range of low energy “dimmerable” bulbs – incandescent/halogen/gu10 replacements.

4) Many/most low energy bulbs (CFLs or LEDs) unless specified are not dimmerable or dimmable.

5) For some ranges of dimmable LEDs you need specific LED dimmer switches.

Frankly, it’s a mess 😉

You should still be able to get mini edison screw lamps as standard filament that can be dimmed, we have these in our uplighters. I think its just the standard 60w bayonet/screw lamps that have been phased out not specialist styles.
Most likely its a crap dimmer. 5x60w =300w(or 1.3A) load so a 400w dimmer should work fine.

We’ve got halogen bulbs in our kitchen and we blew two dimmer switches in about 18 months of installing them, both times when a bulb went. I got fed up and replaced it with a standard switch after the second time, that was 4 or 5 years ago now and no problems since.

I guess the two aren’t always compatible, take the standard switch and see how it goes for a bit.

Great, thanks again all.

I went shopping at lunchtime to buy some bulbs and narrow things down a bit, and I have some further questions!

1) I have some “looks-like-60W”, 46W Osram 100% dimmable halogen bulbs. These are 240v, so a 400W dimmer sounds like the one to go for, allowing de-rating by 25% (according some stuff I read). That about right?

All dimmers are rated by wattage… They are commonly available in 250w, 400w, 600w and 1000w modules. It is important to note that they also have a minimum load requirement of 25w, 40w, 100w and 150w respectively.

2) If my bulbs are 100% dimmable, but the 400W dimmer switch has a minimum load requirement of 40W, does that mean that the lights will dim to 17.4% (40W/5*46W) and then the switch will cut the light to nothing, or can I damage something by turning it down further?

I read this too:

A relatively low level of heat over a period of time can gradually break down the wire insulation, the thermoplastic coating covering the bare wire.  Eventually it cracks and loses its insulating ability causing dangerous short circuits and arc faults.  This is when a little bit of heat over a long period suddenly becomes a lot of heat all at once, a fire.

Which makes a lot of sense because I had a peek behind the dimmer plate last night (3.a) was this naughty or illegal in anyway? Fuse was off) and some of the copper core in the earth wire is exposed. I don’t know whether it was noticeably exposed before he replaced the dimmer last time, or if the last arcing burnt it back.

3.b) Can this be fixed with a couple of wraps of insulation tape? (i.e. perfectly acceptable, or massively unsatisfactory bodge?) I guess even if he does go down this route, he might need to remove the metal surround and possibly some plaster to get back to good sheath and start the insulation repair from there?

Thanks again, I really appreciate the advice. I don’t want to be fobbed off, live in an unsafe house, be left with on/off only if a dimmer is perfectly do-able, or to start suggesting someone get a new electrician if he’s doing nothing wrong!

Right, I’ve had the switch off the wall again for a look-see.

Anything wrong with this picture? 400W should have been fine with the incandescents that were in there. I don’t like the look of the bare earth wire, but it’s connected to the box and the face plate anyway.

Any ideas?

Bare earth wire is fine – that’s how it is inside the rest of the cable.

Looks completely correct 🙁

Doesn’t say MK on it and I tend to earth the switch not the back box (shouldn’t matter) but other than that I’ve missed the deliberate mistake – ie looks fine.

If you’re running dimable halogens it ought to work.

The 400W rating will be for load by the way, not fault – the through fault rating will be higher and the fault make/break rating is probably zero (it will have a fault make capability but I doubt it’s actually formally rated – could be wrong).

Please note I know a little about electricity but on house wiring I’m an interested amateur.

Black is common.
Red is live.

Your live appears to be in common and the ground in live. Which means the lamp is not “on” but a pin will be live.

It wouldn’t be the end of the world but perhaps a dimmer would be less tolerent?

It won’t matter which way round the wires are
With halogens the rating is a bit lower – I think it is 300w for these.

And that’s a very good brand of dimmer module.

Bit confused as to what lamps you have? I’m sure you say small edison screw SES and BC.
If it’s GU10s you need to take a % off the dimmer, I can’t recall what it is as I sit here.

Technically, both red and black are live, and the black should have a red sleeve over it to indicate this 🙂

Cbike may have a point. Although the voltage, being AC, reverses 50 times a second, power flow does not. Some devices (eg certain tapchagers) do not like power flow in the wrong direction.

Annoyed I missed the wires.

Depends on which way the switch cable is connected at the junction box/ceiling rose. ideally the red should be linked to the live cluster and the black should be connected to the live side of the lamp to switch it on (with a red tape marker on it as Spooky says).
Done correctly it should look like this

Anyone else think the Landlord is being very reasonable. If I was him I would put a switch in now, as he will be paying for each callout and materials.

Cbike may have a point. Although the voltage, being AC, reverses 50 times a second, power flow does not

In this case it doesn’t make a difference. In many parts of Europe there isn’t a ‘Neutral’ so you may have two 115V out of phase or what we call ‘Neutral’ actually being the 230V and the other ‘0’. It really shouldn’t make any difference.

In your example the AC reverses and so does the current which is why the power remains the same. It doesn’t matter which way you wire it (in fact I think the Hamilton wiring diagram even has it this way round 🙂 )

It’s a two-way switch being used as a one way switch. I don’t think it matters which way round the feed in and control out go.

Well wwww.ultimatehandyman.co.uk seem like an bunch of cocks. “hotlinking is theft” LOL!

Halogen’s failing can take certain dimmers out…I am an electrian of 30+ year a nd had this in my house, so no probs with wiring…..Buy decent dimmer or derating lamps to 25-35Watt may help but cheap dimmers…they go bang……..Hope the following helps

The need to de-rate a dimmer
When using Mains Voltage Halogen lamps such as GU9, GU10, GZ10 and Linear halogen lamps, dimmers should be de-rated by 25%.

This helps compensate for the additional load due to arcing at the end of the lamp life cycle. This extra load can damage the dimmer. Where possible it is better to use branded lamps such as those produced by GE, Osram, Philips and Sylvania. Generally these have an in-built thermal link and, should the lamp filament short out, the thermal fuse stops the inrush of current which can damage a dimmer. (LIF Technical Statement No.25). Many cheaper imported lamps do not have this thermal link.

Leffeboy – I am aware of the relationship between voltage, current and power, but I tend to work on slightly bigger stuff than dimmers and I’m not aware of their internal design.
Devices vary. A simple AC switch for example would normally cope with reverse power flow quite happily, while a tap changer that uses circulating current to balance load current during the switching operation does not. A tap changer of course being part of the circuitry used to raise or lower voltages on an electrical network, so not a dimmer doing a not dissimilar job.
Not knowing how a dimmer is designed, I refrained from saying there would be an issue, only that there might. I can think of at least one possible design that might have issues, but I doubt it would be used.
I’ll let the people who understand dimmer design tell me if the is an actual issue (probably not but unless you know, just follow the manufacturer’s wiring arrangements).

Cheers igm, did see that already. With 5 of these new 46W bulbs I bought, osram, with the fusible link presumably, I need a dimmer, to allow 230 after 25% derating. So a good quality dimmer rated at 400, down to 300 should be grand. Which is what’s in there now.

sorry igm – didn’t mean to offend. I’m used to much higher power stuff myself but have done a couple of things down in this range. I know what you are referring to now and that’s probably why there is yet another set of dimmers for when you have heavily inductive or capacitive loads

This helps compensate for the additional load due to arcing at the end of the lamp life cycle

Great info. I was struggling to work out why you had to make the extra allowance.

No offence taken Leffeboy. I trust I caused none to you.