DIY Doctor

Main navigation

Probably Very Obvious! Lights Tripped Could This be Dimmer Switch?

Postby Lay86 » Tue Jun 17, 2014 9:57 pm

Absolutely clueless and wonder if you can help.
Lights all blown in bedroom and switch had tripped. I've replaced the bulbs and turned switch back on - nothing working. Is this likely to be a problem with the dimmer switch/ on-off switch ?
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Tue Jun 17, 2014 9:50 pm


Simply Build It

Postby ericmark » Thu Jun 19, 2014 9:43 am

I assume the B6 MCB in the consumer unit has tripped? In theory when a bulb blows it can cause ionisation of the gases in the bulb which is near to a short circuit so every bulb should have an in-built fuse which will rupture in that case and it should act faster than the main protective device stopping one bulb taking out the main fuse but when we moved from main fuse to using a MCB it resulted in the MCB which with a short circuit will trip in 0.01 of a second tripping first. Although a B6 MCB will trip at 6A this is in the fullness of time to trip fast it needs 5 x (The B) 6A = 30A to trip. With a C6 it's 60A and with D6 it's 120A so house should have a B6 trip. When the RCBO came out which replaces the MCB with extra earth leakage protection there was a move to using C6 and where silly 50mm spot lights have been used often it needs more than 6A so 10A trips have been fitted although really not permitted where 6A ceiling roses are used.

The standard dimmer "Should" take the 30A for the 0.01 seconds without failing but some do blow even with that power however where the trip has been swapped for a C6 or B10 MCB it will often take out the dimmer when the bulb blows as often today the built in fuse that should be in the bulb is in fact not there.

So yes it is likely the dimmer needs replacing but do ensure the trip is no bigger than a B6 first. If it is then use a standard switch not a dimmer.

Dimmers are really a phase which has passed you can still get them but for a CFL or a LED bulb to work with a dimmer means paying near double for the bulb and the bulb and dimmer have to match with have leading and lagging it is so hard to get them to work correctly hardly worth the cost.

I have a triple switch at door main, left hand bedside and right hand bed side lights. Each side of bed I have double switch main and that sides bed side lamp. This works far better than dimmer it does not wake partner with bed side lamp.

It would seem there is still a legacy with remote control light switches often having no option but to have a dimmer although other options are now appearing on the market. There are two types of dimmer bulbs.
1) Designed to work with dimmer switch.
2) Designed to work with simple on off switch.
The latter type does mean when bulb blows replacing bulb auto replaces dimmer so no problems like you have now in having dimmer switch replaced when bulbs blow.

On average I would say bulbs having ionisation as they blow likely happens 1 in 10 times a bulb blows you often see a bright flash when it blows if it ionises the gases. So on average expect to swap dimmer around every 10 bulbs. As I say some dimmers do seem to stand the bulbs blowing but when I have a dimmer fail it comes out now only one left in the house.
Rank: Project Manager
Posts: 2697
Joined: Fri Oct 02, 2009 8:49 pm
Location: Llanfair Caereinion, Mid Wales.

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics