Return to the Electrical Wiring Forum | Post a Follow-Up

Dimmer Question

Posted by javachik (My Page) on
Tue, Nov 16, 10 at 6:54

I had a handyman (licensed for "simple" electrical work, but not master electrician) hang 3 new ceiling light fixtures and install dimmer switches on 2 of them (a 5-bulb and a 2-bulb). Each of the fixtures is rated for 100w incandescent bulbs, which I used. However, the dimmer switches get hot at full power and lower power. I replaced the 100w bulbs with 75w bulbs. Same problem. Any suggestions?

Follow-Up Postings:

RE: Dimmer Question

You need to look at the dimmer ratings. The cheapest ones are rated at 300W, though you can get them at 600W or 1000W. The most likely result of you exceeding the rating is that the triac within will fry (most likely the dimmer will cease to dim anymore).

However, it's not uncommon for these things to get warm. The whole front plate is metal to try to dissipate some of this. When used in a multigang box, you may have to derate it (read the dimmer instructions).

RE: Dimmer Question

The dimmer is rated for 600w installed separately or 500w installed in a 2 gang box (my case). So, I believe that part is OK especially since I even reduced to 375w.

Perhaps the temp is normal as you say, but it appears strange to me.

RE: Dimmer Question

The semiconductor device in the dimmer (a triac) has a small voltage drop when it is conducting.

If the lights are at full intensity and pull 375 watts, the triac is passing ~3.2 amps. If it is dropping just 2 V the power dissipated in the triac is 6 watts.

While not a lot of power it will cause the faceplate (used as a heat sink for the triac) to heat up.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Electrical Wiring Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here