Metal Boxes in Residential???

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The solution is obvious, they should require cooling fans in all plastic boxes in case someone wants to dim 1200 watts of load with a 600 watt dimmer.
 
And no installing with nails either, or little #10 screws. Should use 1/4" x 1 1/2 lag screws. No skimping on this job.
 
Yea right. Most customers don't want to pay for a slop job, much less a custom conduit job. I've done EMT in warehouse offices with wood studs, sometimes in sheds, garages, etc. where it seemed needed. Never for interior wall in a house.
 
Maybe not, but if it reduces questions & complaints, isn't it worth it? I did a job for a friend who worried that his dimmer got so hot, didn't seem safe. I went over, put a full load on it & sat for an hour, reading the paper. To me, it was barely warm. I guess he thought it should be cool to the touch. Shortly afterward, another thread here dealt with that issue. I decided then I'd use a metal box if I knew dimmers were involved. The metal does absorb some heat & dissipate it into the wall if the dimmer heats up. Plastic would contain the heat, not dissipate it. Then again, the only dimmers I saw get truly hot were way overloaded. Have to pay attn to that too.
 
hurk27 said:
unless of course you try to dim 1200 watts of lights on a 600 watt dimmer like I have seen:roll:
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Hurk,
Have seen customers with very sensitive hands,
so that what I see as warm (120 degrees) feels like 'hot' to them.
600 W on a 600 W dimmer can get 'warm'. Maybe too 'warm'.

The metal box can cool things down enough,
so the HO sees the beauty of the well hung chandelier.
 
hurk27 said:
If you want to test this theory, just grab a small propane torch and hold a metal box
. . . now try this with a plastic box,
you will melt almost the whole box away
before your fingers start feeling the heat from the box.
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Such an Acid Test ! :mad:

In school, we used a thermister for a "Constructive Test"
and our fingers for a "Destructive Test". :roll:
 
K8MHZ said:
It's not that simple. In a house there are turns that need to be made that are really tough to do with pipe simply due to it's inherent physical limitations. There are other issues as well, but it's way easier to run EMT in a commercial building than in a wood frame house, and I speak from actual experience.
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K8MHZ,
In the early 70's, we roughed apartments (wood frame) with EMT.
There are some techniques that make it do-able,
but at 700' per workday per man it is obvious the labor cost is high.
 
K8MHZ said:
It's not that simple. In a house there are turns that need to be made that are really tough to do with pipe simply due to it's inherent physical limitations. There are other issues as well, but it's way easier to run EMT in a commercial building than in a wood frame house, and I speak from actual experience.
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I am no supporter of using pipe for wood framed single family dwellings but the fact is some areas require it so obviously it can be done. Like anything I imagine experience is the difference.
 
As I remember you are allowed to use FMC at those places where you can't get EMT around. For instance in those pictures I talked about I remember a whip on the end of an EMT run for the later installation of a cut-in box for a light by the front door. The hi-hats in the kitchen ceiling were all hard piped though.

As for those dimmers, when was the last time you saw one actually in contact with the box? Nearly always the box is set back the legal 1/4" and the dimmer is held tight to the drywall by the screws. The only time I can see a metal box helping with heat dissipation is with a mud ring and it's wide lip that is installed dead flush with the front of the drywall and the dimmer sitting right on it. Since that isn't going to happen IMO plastic is just as good as metal.

-Hal
 
PetrosA said:
I would tell the customer this:

Plastic is inherently SAFER. There is no way for wires to energize the box, then the yoke, then the little screws on your switchplate which, if the ground wire malfunctioned, would carry 120V and shock you. Because metal boxes are "likely to become energized" electricians have to spend extra time to ground them to protect the final user.

Plastic boxes have more space inside for air flow and cooling of wires which results in a more efficient system.

Because plastic boxes are larger inside and "breathe" better, the expensive devices like GFI outlets and dimmer switches install easier and last longer.

Metal boxes still have their place, but in my expert opinion plastic is the better way to go most of the time.

Just say it with conviction :)
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Besides being dead wrong on some - wait all - points. One could say anything with conviction - to include fausehoods.
 
hbiss said:
...
As for those dimmers, when was the last time you saw one actually in contact with the box? Nearly always the box is set back the legal 1/4" and the dimmer is held tight to the drywall by the screws. The only time I can see a metal box helping with heat dissipation is with a mud ring and it's wide lip that is installed dead flush with the front of the drywall and the dimmer sitting right on it. Since that isn't going to happen IMO plastic is just as good as metal.

-Hal
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The device does not have to be touching the box for the metal to improve the heat transfer. The convected and radiated heat from the device will heat the inside surfaces of the box. The box that is more conductive will transfer the heat from inside the box to the wall cavity better than the box that is less conductive.
Does it make an real difference with a device that is being used within its design...not likely.
 
The box that is more conductive will transfer the heat from inside the box to the wall cavity better than the box that is less conductive.

You would have better luck with that if the box had ventilation holes on the top and bottom to encourage the flow of air by convection up through the box driven by the hot dimmer body. What you discribe can only make a marginal difference at best.

-Hal
 
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