Metal Boxes in Residential???

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glene77is said:
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.
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You have a point. Our hands take a beating every day & get desensitized to heat & pain. When I worked in an office, my hands were more sensitive. Lots of people I know are office people & have a more sensitive touch.
 
Speaking of dimmers, does anyone else hate the models with break off tabs? You usually have to start removing tabs to get 2 dimmers side by side. What poor design. Of course, each lost tab is lost wattage capacity.
 
jmellc said:
Speaking of dimmers, does anyone else hate the models with break off tabs? You usually have to start removing tabs to get 2 dimmers side by side. What poor design. Of course, each lost tab is lost wattage capacity.
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Pretty much every dimmer I have ever installed. Never gave it much thought.
 
jmellc said:
Speaking of dimmers, does anyone else hate the models with break off tabs? You usually have to start removing tabs to get 2 dimmers side by side. What poor design. Of course, each lost tab is lost wattage capacity.
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where else do you suppose they'll squeeze the heatsink in while keeping the same profile that fits in a standard box and underneath a wallplate?
 
brantmacga said:
where else do you suppose they'll squeeze the heatsink in while keeping the same profile that fits in a standard box and underneath a wallplate?
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Could they plate the dimmer itself? That would be a fair surface area of metal.
 
hbiss said:
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
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Even if the box is set back a bit, the dimmer radiates heat around itself, heating the air in the box & the box itself. The metal box is being heated from inside & is facing cool or at least less heated air in the wall. So it dissipates at least part of the heat into the wall. You can put your hands a foot away from a woodstove with a hot fire & feel plenty of heat even though you aren't touching the stove.
 
jmellc said:
Could they plate the dimmer itself? That would be a fair surface area of metal.
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Wouldn't that still be a problem with multigang applications?

I've seen 1000 watt dimmers that are self trimming with the heatsink - you do not use them in multigang applications as they are too large to fit next to another device.
 
Thermo dynamics

Thermo dynamics

3 rules of thermo dynamics
1 can't win
2 can't loose
3 can't get out of the game

The heat has to go some where.

I tell customers if the heat bothers them I will be more than glad to put a regular switch in there for them. I also inquire what the wattage and how many lights are involved. Then the up sell of a higher wattage dimmer. Plastic or metal, wont matter, they are rated for volume, the heat is a function of load.
 
Back to the original topic, the only viable reason that I can see for using metal over plastic for your junction boxes would be from the common rules regulating multifamily homes and commercial buildings over 3 stories - build-up of toxic fumes from burning plastic during a fire.

Clearly this argument is overshadowed by the NM cable vs. MC/Pipe debate, and the fact that the odds of a home fire are reduced exponentially by newer standards, technology (AFCIs, etc.), and quality construction practices from qualified/licensed/experienced electricians such as ourselves. :cool:

Everything else, as stated ad-nausium earlier, boils down to personal preference and competitive pricing of materials. Piping homes in EMT or in the deck with PVC might be reassuring, but I'd never win a bid if I had to price that against the competition.
 
rebturtle said:
Back to the original topic, the only viable reason that I can see for using metal over plastic for your junction boxes would be from the common rules regulating multifamily homes and commercial buildings over 3 stories - build-up of toxic fumes from burning plastic during a fire. ...
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While that is often the cited reason for such rules, it doesn't make a lot of sense. The amount of non-metallic, toxic smoke producing, building materials is very small compared to the same materials in the building finishes and furnishings.
 
Reb, welcome to the forum! :)

rebturtle said:
Back to the original topic, the only viable reason that I can see for using metal over plastic for your junction boxes would be from the common rules regulating multifamily homes and commercial buildings over 3 stories - build-up of toxic fumes from burning plastic during a fire.
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Most often, when I've used metal boxes in otherwise-all-plastic jobs, it has been when mixing old and new wiring in a remodel, as a way of bonding existing BX or conduit runs.

Of course, there are other examples, such as for surface-mounted devices and ceiling-fan boxes.
 
don_resqcapt19 said:
While that is often the cited reason for such rules, it doesn't make a lot of sense. The amount of non-metallic, toxic smoke producing, building materials is very small compared to the same materials in the building finishes and furnishings.
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It also does not make sense that in many commercial applications use of NM cable, plastic boxes, PVC raceways is prohibited because of toxic fumes given off when these items burn. Yet they are ok to install in dwellings where people sleep while this stuff just happens to start a fire. At least in most commercial applications people are not sleeping, or they at least have even better fire alarm systems than what is typical in a dwelling. Commercial buildings are often better designed to inhibit the spread of fire better than dwellings also.

Besides why is the wiring going to start the fire? If installed according to NEC, that risk should be fairly minimized.
 
kwired said:
It also does not make sense that in many commercial applications use of NM cable, plastic boxes, PVC raceways is prohibited because of toxic fumes given off when these items burn. Yet they are ok to install in dwellings where people sleep while this stuff just happens to start a fire. At least in most commercial applications people are not sleeping, or they at least have even better fire alarm systems than what is typical in a dwelling. Commercial buildings are often better designed to inhibit the spread of fire better than dwellings also.
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Level of liability, I guess.

Besides why is the wiring going to start the fire? If installed according to NEC, that risk should be fairly minimized.
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Wiring could be a casualty of a fire, not the cause, and still emit toxins.
 
LarryFine said:
Level of liability, I guess.

Wiring could be a casualty of a fire, not the cause, and still emit toxins.
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That is definately true, but how much toxin is emitted by the wiring system vs what is in the rest of the building or furnishings that will also be casualties of the fire?

Most deaths in fires come from suffocation from the combustion byproducts. They are given off very rapidly and unless the fire is limited to the wiring system, I'm willing to guess that if a building occupant was to succumb to the toxins in the air, it happens long before wiring systems are much contribution to the level of toxins in the air.

You ever try to burn PVC conduit? You are more successful at it if you already have a fire that is fueled by something else.
 
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