Help wiring a dimmer switch please.

Hi
I am reasonably competent with basic eleccy DIY - fit socket extensions, wired up my shed & garage etc - but i've never fitted a dimmer switch !
Anyway the one we have in the house has gone pear shaped and the missus wants to keep it and got a new one from B&Q. Instructions are useless.
The old one has 2 connections one marked "Com" which has the thick red wire and one of the thin red wires connected; and one marked "L" with the other thin red wire connected, - usual earth to face plate.
The new one has 3 connectors L1, L2 & then another with a strange symbol on it - as far as I can glean from the instructions it is for a transformer (?) - low voltage supply ?
Have we got the "wrong" dimmer switch ? If not how should I wire it up.
Thanks for any tips. -- JB - replace myname with john(dot)brennand
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

wire
on
(?)
Can you describe the funny symbol please.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It looks like the "approximately" symbol (~) or an "s" on its side with a forward slash through it a bit like this - but "curvy"
____ / / \/ /\____/
Cheers
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

IIRC, this indicates the switched AC output, so would be the live output going to the load. Check the connections on the dimmer (*unconnected to anything*) with a continuity tester (with multimeters from Maplin so cheap these days, there's no excuse not to have one!) - you may find that L1 and L2 are actually commoned to allow further switches to be daisychained.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

L1 and L2 terminals always indicate a two way switch. Are you saying some ignore this convention? I wouldn't have thought it complied with the relevant BS if they did.
--
*Age is a very high price to pay for maturity.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Is there another switch close by? The second wire connected to 'com' probably goes to this.

L1, L2 and common are the standard three terminals of a two way switch, and many dimmers do actually have a two way switch fitted. I'd just treat the one with the strange symbol as 'com' - and even although it's designed for low voltage lighting it will be ok with normal. No 'low voltage' dimmer actually works on the low voltage side - they are simply of different (more expensive) design to cope with the inductive load, but will work ok with a normal one.

--
*When the chips are down, the buffalo is empty.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
JohnB wrote:

Dimm,ers just go in series with the live supply, with the neutral carried straight through.
Your new one has a chanegover switch - thats all - bet its a push on push off switch rather than a rortary click ...thes can be used with anothetr changeover swicth for two way control...
Try the 'odd' terminal and eiher of the other two. In fact the only way to wire it wrong is to use L1 and L2, in which case it simply wont work.
Polarity is not important, since its simly AC passthrough.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.