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Do I need to reduce (de-rate) the dimmer rating when dimming mains halogen lamps?

When using mains Tungsten Halogen bulbs with rotary dimmers the maximum loading of the dimmer must be halved.

For more information see the chart and text below
Single Dimmer switch

Tungsten/Mains Voltage Tungsten Halogen Lighting
Most Tungsten lamps can be dimmed; these include standard GLS lamps, candle lamps, reflector and mains voltage Tungsten Halogen
lamps etc. Tungsten lamps of mains voltage halogen type (GZ10, GU10 or G9) can be dimmed using standard Tungsten dimmers. However, to
protect the dimmer, it is important to de-rate the dimmers maximum rating by 50%, (e.g. for dimmer rated as SOW- 400W, it’s Tungsten Halogen
lamp rating becomes SOW- 200W). This de-rating requirement only applies to Plate and Grid dimmers rated up to 1500W, for other dimmers,
observe individual product guidelines. While observing maximum dimmer ratings, also ensure that the connected load is not less than the minimum
rating of each dimmer, otherwise the lamps may flicker and the dimmer may fail
Dimmer power rating chart in Watts
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