Hi All,

I have read the when installing mains halogen spotlights, you need to have a
dimmer rated to twice the actual rating of the load.

The range of switches we are using (the chrome crabtree ones from Screwfix)
has a dimmer with a 400w maximum which isn't quite enough the arrangement we
have (240w of normal light lightbulbs, plus 105w of Halogen) .. this would
beed 445w capacity.

Can anyone explain why the 2x overrating is needed, and it a flexible rule
(i.e +/- 20%)

Cheers
Chris

Can anyone explain why the 2x overrating is needed, and it a flexible rule
(i.e +/- 20%)

There are a number of issues. There might be a slight inductive effect from
any LV transformers.

There is a much higher inrush current on halogens as halogens warm up from
cold, compared to incandescent. They also have particularly powerful
ionisation shorts when they blow.

Christian.

In article ,
Chris Styles wrote:
I have read the when installing mains halogen spotlights, you need to
have a dimmer rated to twice the actual rating of the load.

It depends on the dimmer. It should say on the box or instructions. If it
doesn't, it will be safe with any load (other than inductive) up to its
maximum.

--
*I used up all my sick days so I called in dead

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
Chris Styles wrote:
I have read the when installing mains halogen spotlights, you need to
have a dimmer rated to twice the actual rating of the load.

It depends on the dimmer. It should say on the box or instructions. If it
doesn't, it will be safe with any load (other than inductive) up to its
maximum.

--
*I used up all my sick days so I called in dead

Dave Plowman London SW
To e-mail, change noise into sound.


OKay, so as all the Halogens i plan to use are mains voltage there are no
transformers, so the inductive load is very little.

So in my case 400w should mean I can dim 400w total of incandescent and
halogen.

Sadly, the only was to read the instructions is to buy it :-( I could try
Crabtree customer support i suppose...

Cheers
Chris

In article ,
Chris Styles wrote:
It depends on the dimmer. It should say on the box or instructions. If
it doesn't, it will be safe with any load (other than inductive) up to
its maximum.


OKay, so as all the Halogens i plan to use are mains voltage there are
no transformers, so the inductive load is very little.

Near enough non.

So in my case 400w should mean I can dim 400w total of incandescent and
halogen.

Sadly, the only was to read the instructions is to buy it :-( I could
try Crabtree customer support i suppose...

A quick glance at the Screwfix site shows downloadable instructions for
the Crabtree dimmer I looked at. And it certainly was a modern 'any' load
type with soft start and overload protection.

--
*Is there another word for synonym?

Dave Plowman London SW
To e-mail, change noise into sound.