Dimmer selection and Wiring

amh1 · Posted: Thu Jan 12, 2006 6:18 pm Post Subject: Dimmer selection and Wiring

My Situation:
The existing wires I have to connect a new 1 gang 2 way dimmer switch (I only need 1 way wiring) are 3 sets of cables each with red, black and earth. On the back of the old switch I am replacing, 2 of the red wires were twisted together and wired into the "top" terminal on the switch and the other red wire was connected to the other terminal on the switch. The 3 neutral (black) wires are connected together and junctioned off separately onto a plastic junction block. The earths are attached to the earthing point inside the back casing.

The terminals on the new dimmer are L1 L2 and C.

What I did:
I connected the Dimmer switch up with the single red wire in the L1 terminal and the 2 red wires that are twisted together, in the C terminal. I earthed the switch plate with a new piece of earth wire connected to the earth terminal on the back casing.

What happened:
The light turned on, dimmed up and down successfully, then shorted out over the L2 terminal (which had nothing connected to it), tripping the main lighting fuse, when I turned it off.

Question 1:
Have I selected the correctly rated dimmer switch? The dimmer I used was rated for 250W. The light is a mains ceiling mounted GU10 halogen with 4x50W bulbs.

Question 2:
Does my wiring on the dimmer seem correct? Should I use a live test tool to establish which red wire is the live and which is the switched live, or can anyone tell me given the way 2 of the red wires are twisted together and 1 is a single wire.

Carloss · Posted: Thu Jan 12, 2006 6:46 pm Post Subject:

Hi,

I'm guessing you have a Feed in and Feed Out and a switch line. Therefore the way you have wired it is correct.
The rating of dimmer is also correct.

Only thing i can suggest is that the dimmer is faulty. Try re-wireing it into a standard 1gang 1way or 2way switch and see if it trips.

carlos

breezer · Posted: Thu Jan 12, 2006 6:49 pm Post Subject:

how do you know it shorted to L2

and the dimmer is too small anyway, halogens need a twice as the lamp rating for the dimmer, unless suitably made for halogens.

so 200w of halogen lights need a 400w dimmer min.

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amh1 · Posted: Thu Jan 12, 2006 6:53 pm Post Subject:

Well the back of the L2 terminal was charred and a little melted. I guess if you think the wiring was correct then its the rating of the dimmer. I need to get a 400W dimmer rather than the 250W I melted earlier today?

Thanks for your replies.

Carloss · Posted: Thu Jan 12, 2006 6:53 pm Post Subject:

Thanks breezer.... learn something new everyday.. i never knew that about dimmers!

carlos

ban-all-sheds · Posted: Thu Jan 12, 2006 6:58 pm Post Subject:

Note what breezer actually wrote:

and the dimmer is too small anyway, halogens need a twice as the lamp rating for the dimmer, unless suitably made for halogens.

Many dimmers these days are made with halogens in mind, so a 250W might well be OK - you need to check the actual specifications to see what it says.

As for the shorting out - how was anything able to touch the L2 terminal? Did you have loose wires in there, or unsleeved earths or something?

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breezer · Posted: Thu Jan 12, 2006 6:59 pm Post Subject:

Carloss wrote:

Thanks breezer.... learn something new everyday.. i never knew that about dimmers!

i am not saying you don't believe me, but have a search for dimmers etc, you will find as i have said.

amh1, that is 400w minimum, so 450 or 500 will be ok too.

but as i also said some (not all) do not have to be down rated

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Carloss · Posted: Thu Jan 12, 2006 7:03 pm Post Subject:

Breezer,

I wasn't being sarcastic, i was not aware of that. I just assumed you could take the maximum load e.g.200W and use the next up rated dimmer in this case 250W.

Thanks again,

carlos

breezer · Posted: Thu Jan 12, 2006 7:07 pm Post Subject:

Carloss wrote:

Breezer,

I wasn't being sarcastic,

i never thought you were being sarcastic, its just in case you or any one else reading this post in the future doesn't believe me.

as you said its amazing what you can find out on these forums, i for example have learnt a lot about boilers

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Carloss · Posted: Thu Jan 12, 2006 7:17 pm Post Subject:

Breezer,

I totally agree with you... i take away a lot of information from this forum and use it day in day out.

I notice your from Luton, i done a job at Pepperstock just outside Slip End-is that close to you?

Do you also work around that area? maybe you could e-mail me if you don't wish to post here.

Carlos