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#27613 - 07/22/03 06:47 PM How hot is TOO hot?
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
I installed 10, 75 watt PAR30 narrow floods, controlled by a 1,000 watt dimmer.
It is in a 3-gang box with a 600 watt dimmer next to it, controlling 2, 45 watt floods, and a single pole switch next to that, which controls nothing yet.
The 1,000 watt dimmer has one fin removed, which derates it to 800 watts. With the lights on full, it is almost too hot to keep my hand on. I am thinking about replacing it, but maybe it is supposed to be that hot?
Thoughts, anyone?

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#27614 - 07/22/03 07:00 PM Re: How hot is TOO hot?
Electric Eagle Offline
Member

Registered: 04/20/02
Posts: 928
Loc: Alpharetta, GA
I emailed Lutron with this question once and they told me it's safe and normal up 150 degrees above ambient room temp. So in a 72 degree room, 222 would be ok.

They told me to replace the plate screws with nylon screw and the heat wouldn't disipate to the plate. It works. We now just put in nylon screws whenever we put in a dimmer to prevent callbacks. Almost every homeowner was calling back afraid their house was going to burn down.

What changed to make the new dimmers so hot, the old ones didn't get that hot.

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#27615 - 07/23/03 01:00 AM Re: How hot is TOO hot?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Hey, Redsy,
That doesn't sound quite right to me.
 Quote:
With the lights on full, it is almost too hot to keep my hand on.

I was always taught that at full current(max.light)the dimmer carries little current.
To my way of thinking, the state that you should be testing it at is, just next to full dim, as this is where the Triac, should be switching the most load current.
But even so, I've always had my doubts about Flush-mounting dimmers in walls, especially were Fibreglass insulation is used, there's just no air circulation around the Heatsinks and chances are, the Triac, will burn out.
Also, what are the chances of you installing a Remote Dimmer unit, say up in a Roof-Void, where it has got a bit of air around it?, most only need 3-4 cores to effect this.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#27616 - 07/23/03 06:31 AM Re: How hot is TOO hot?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
What you're describing there applies to a good old-fashioned series rheostat dimmer, but triac units don't work quite the same way.

With the rheostat, as you insert resistance to dim the light you get heat dissipated by it due to I^2*R.

With a triac unit, the RC dimmer control determines at which point in each half cycle the triac is triggered into conduction. Before that triggering point, the current is practically nil (just the tiny leakage through the PN junctions).

There's a small amount of voltage drop across the triac when it's conducting. As you increase the brightness of the lamp, the triac is conducting for a greater portion of each half cycle, therefore it gets hotter.

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#27617 - 07/24/03 03:57 AM Re: How hot is TOO hot?
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Thanks, guys.
I will probably change the dimmer to see if it helps. If not, I'll know that the heat is OK.
Eagle,
200+ degrees? Wow!
Paul,
Thanks for the explanation. I know that modern dimmers are SCR, but I, like Trumpy, was still expecting more heat at lower levels.

[This message has been edited by Redsy (edited 07-24-2003).]

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#27618 - 07/24/03 05:32 PM Re: How hot is TOO hot?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Paul,
Thanks for that correction,
Triacs and SCR's sre not really something that I have a lot to do with.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#27619 - 07/24/03 06:17 PM Re: How hot is TOO hot?
LoneStar Offline
Member

Registered: 06/03/03
Posts: 14
Loc: Victoria, TX 77901
tell them it serves as a cigarrette lighter to!! Its one of them new fancy kinda dimmers LOL

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#27620 - 07/25/03 02:11 AM Re: How hot is TOO hot?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Here's a Basic outline of the dimmer and triac.

Go here for loads more links .

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#27621 - 07/25/03 04:25 PM Re: How hot is TOO hot?
electure Offline

Member

Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
A dimmer working @ 222°? Nylon plate screws?
Wow, I'm really confused here.
Would that not melt nylon screws?
What about the 60° wire that might be connected to the dimmer? (it doesn't matter if it's 90°), that still doesn't equate to 222 F.

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#27622 - 07/25/03 07:01 PM Re: How hot is TOO hot?
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
A couple of links roughly agree with postings so far. Apparently a 70°C rise over ambient is acceptable for plastic surfaces that may be touched. That corresponds to a 126°F rise—196°F in 70°F air.
http://www.coolingzone.com/Guest/News/NL_May_2003/Biber/Biber_May_2003.html states:

Note that aside from product safety, there is significant importance given by most users to the surface temperature of electronic equipment – if it feels hot, it must be running hot, and therefore the perception is that the equipment is not functioning properly. In my experience, surface temperatures around 50 C are subject to this perception, and the UL touch temperature limit for plastics is quite a bit higher (up to 70 C rise above ambient – 95 C!).

A CSA chart on touch temperatures… {Note differences for metal, vitreous and plastic surfaces} http://www.coolingzone.com/Guest/News/NL_May_2003/Biber/UL_touchtemp_table.pdf

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