Do have dodgy electrics or just the wrong dimmer?

[jarvss]

Hi I would be very grateful if anybody is able to advise me about a dimmer problem.

I am not an electricician but have in the past added sockets and fixed what was a broken ring in my house left by the previous owners so have some knowledge and experience.

2 years ago we had a new extension built with all new electrics installed by a qualified elctrician onto a new and seperate fuse box from the old part of the house In our new kitchen we have a double dimmer switch which has 8 LV downlights on one switch and 7 on the other. The 7 also have a second on/off switch in the room. They are powered by Electronic transformers (which as I understand are different from wire wound but out of my depth on that one). A few weeks ago the dimmer with the 8 lights made a sparking noise when I turned on and the light stopped working. I checked the socket and it is rated up to 400w on each size. By my calculation we 400 on one side and 350 on the other. My reading on the net seems imply that I should have sockets rated up to 800w for this and also many of the dimmers I found say a max of 5 transformers on the circuit. I'm struggling to find one fits the bill.

We took the opportunity last week to raplace the cheap switches in the extension with MK switches. As a stop gap another similarly rated double dimmer that was being replaced and I put this into the kitchen. As soon as I tried to use it it sparked and broke the switch again. I tried using just a normal double on/off switch instead and it worked fine.

Sorry for the long email but my question is does it sound like I have a wiring issue (eg a short or something) I'm guessing not as just a normal switch on the circuit works fine. Or is it just because there is a surge of more than 400w blowing the switch maybe? If the latter can anybody recommend a suitable dimmer? We are currently looking at using touch /infrared dimmers if possible.

Many thanks if you manged to reach the end of this. Any advice a suggestion gratefully appreciated. I'm happy to get in a qualified electrician in but have a dilemma that a new electrician might say we need to replace half the electrics (when we don't) and the old one might cover up (if thats what happened in the first place) a bad job.

Jarv

 

[ban-all-sheds]

If it all works OK with switches but dimmers give up the ghost then doesn't that mean it's the dimmers which are the problem?

But dear god, man - 15 lights, 750W for a kitchen? I can light my whole house for that. What were you thinking of?

 

[flameport]

If a normal switch works, then the problem will be the dimmers - either they are not compatible with the transformers you have, or the dimmer rating is too low.

You will need to find out exactly what kind of transformers you have got (by removing at least one and seeing what is written on the side) and then select a dimmer which is compatible with them.

They should either be 'trailing edge' or 'leading edge' and must be used with dimmers of the same type, and as you have found already, most have restrictions on how many transformers can be used on each dimmer.

Dimmers above 400w are available, but they generally require a larger mounting plate.
Another option could be to change to 230v downlights which do not have transformers. The same wiring can be used.

 

[bhm1712]

what is the range on the LV downlight transformers? 20-60watt?

Is it possible that the lamps were originally all 50 watt (8 lamps with a total of 400 watts = 50w per lamp) and you have replaced some lamps with 60 watts?

If this is the case you may have taken the load over the limitations of the dimmer switch.

 

[Taylortwocities]

what is the range on the LV downlight transformers? 20-60watt?

Is it possible that the lamps were originally all 50 watt (8 lamps with a total of 400 watts = 50w per lamp) and you have replaced some lamps with 60 watts?

If this is the case you may have taken the load over the limitations of the dimmer switch.

All of which makes no difference at all.
The bit you are missing is that when you are using dimmers with electronic transformers you usually have to add up the VA ratings of the transformers, not the lamps connected to them.

So 6 x 60VA transformers with 50W lamps on them make 360VA not 300VA. That's where many folk go wrong.

Also, many dimmer manufacturers will state a limit on the number of transformers that the dimmer will handle.

There are guides to this like this

http://www.tlc-direct.co.uk/Technical/DataSheets/Systems/DimmerGuide.htm

 

[bhm1712]

me = dumb-ass

apologies

Dont you find it strange that they have been working ok for 2 years? you would think if he had bought the same rating dimmer then it would also work! unless there are some ratings on the new dimmer that dont match the old

 

[Taylortwocities]

Sometimes dimmers will work for quite a while, on the edge of their capabilities.. Annoyingly buzzing away next their buzzing friends, getting all hot and bothered, like a sack of angry bees.
One fine day it will struggle no more and die.
Sometimes it will only take a little extra current (eg a lamp blowing) to turn the dimmer into an expensive fuse.

You pop out to the wholesaler and buy another dimmer of the same rating not knowing that the maker's instructions say to de-rate their dimmers by 30% when used with transformers. Or that theirs is leading edge and you need trailing edge.

So just swopping one 400VA dimmer for another 400VA dimmer does not guarantee success.

 

[jarvss]

Many many thanks for all of the replies.

But dear god, man - 15 lights, 750W for a kitchen? I can light my whole house for that. What were you thinking of?

The kitchen is 6m x 5m and the lights are all as we were advised by the electrician that did the installation. Generally we dim them although there times when one half (the 8 or the 7) are on full.

The transformers say 20-60Va so I guess we have 480Va on one side and 420Va on the other but what does that mean with regard to the dimmer as it just says 60-400W and 400W MAX on each switch? Also how do I know if I have or need leading or trailing edge as this isn't written on the dimmer or the transformers?

Unfortunately using a double width socket isn't possible due the space, door one side and kitchen units on the other.

Some of the IQ dimmers that I saw said that they had some of protection that implied they would shut off if too much power went through them. Could I use these without the concern of frying them?

Many thanks.

 

[securespark]

You could fit a grid system into a 2 gang box mounted vertically. That would allow you to fit two larger dimmer modules in there.

 

[flameport]

Some of the IQ dimmers that I saw said that they had some of protection that implied they would shut off if too much power went through them. Could I use these without the concern of frying them?

Yes, but this won't solve your problem, since if overloaded they will either switch off or worse, flash on and off at intervals.