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Dimmers and Heat

Submitted by DonHester on Thu, 07/14/2016 - 19:12.

Dimmers and Heat. Wenatchee Home Inspections

All dimmers will give off heat. That's why their mounting yokes (brackets, straps) are made of aluminum and have fins to act as heat sinks to dissipate excess heat generated by the dimmer switch. The question is, how much is too much heat?

Dimmer switch in Infrared and visible light.

When you install dimmers in a multi-gang box and if that installation requires you to remove or bend off part of those mounting yokes fins to install in adjacent gangs you will have to de-rate the dimmer switch depending on how many fins are removed. This will limit the total capacity of the dimmer, e.g. a 600w dimmer may now be a 400w dimmer. All manufacturers' installation instructions indicate to de-rate accordingly to amount of fins removed.

Below is a graphic from Lutron showing de-rating dimmer switches when fins are removed

Lutron example

From Lutron

Standard multi-gang:

Ganging is the side-by-side mounting of 2 or more dimmers or accessory devices under a multi-gang wallplate. Standard multi-gang installation:

Uses standard multi-gang electrical backboxes

Uses standard multi-gang wallplates

Requires fins to be removed from dimmers for proper spacing.

May require derating (i.e., reduction of dimmer capacity). See capacity derating charts.

Lutron Ganging De-rating Table Example

Per the bi-national (US & Canada) standard UL 1472 • CSA-C22.2 No. 184.1, when tested in an ambient test lab temperature of 25°C (77°F), surfaces accessible during normal operation are permitted to not exceed 60°C (140°F) (i.e., 35°C(63°F) temperature rise over tested ambient). That is pretty warm when you touch it. And for the Heat Sink (i.e., mounting yoke, bracket, strap) behind the faceplate it is permitted to not to exceed 90°C (194°F). You will be moving your fingers pretty quick when you touch that. Both the UL and CSA consider these limits to be safe, albeit very warm but safe… I guess.

If you have temperatures that exceed these limits there are a possibility that the dimmer is either overloaded or another possibility that there was damage where the fin was bent off at the mounting yoke. There may be a case where the bend might have extended too far to where that rivet or fastener that mechanically and thermally secures the heat sink to the triac or quadrac of the dimmer. If that thermal junction is disturbed or damaged, you might get "hot spots" and the dimmer should be replaced.

So as you can see these dimmer switches are designed to handle a good amount of heat.

“It ain't the heat, it's the humility.”

Yogi Berra

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…

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Instructor- Fundamentals of Home Inspection- Bellingham Technical College

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www.ncwhomeinspections.com 509-670-9572

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Dimmers and Heat