Plastic or metal electrical boxes?

[grsthegreat]

ok..heres my 2 cents worth. I'm an electrical contractor..have over 30 years in the industry.

I have no problems with the plastic boxes, but their quality does vary. i've tried the blue boxes from home depot, and usually break quite a few of them while nailing them on the wall. However, the black BOWER brand boxes from my supply house, which are a little more $$$, NEVER break. you get what you pay for.

I always use plastic FAN RATED boxes for all surface mount light fixtures. they can support up to 150# stationary load or 75# fan ratings.

the above is for residential.

For commercial i always use metal boxes. Why the difference, because on commercial work i generally use metal EMT conduit, flex conduit or MC/BX metal clad wiring as per code here in Idaho. The code has loosened up some and now allows romex wiring in commercial, but i wont use that. Doesn't allow for changes later like EMT pipe does. And commercial businesses are always changing. When you use metal conduit, you HAVE to use metal boxes.

i really feel that there is no problem with plastic boxes in residential use. Most outlets have something plugged into them, and remains plugged in them forever. They don't have constant movements. That being said, i use metal boxes in all my shops and garages.

When i wire horse barns, i use metal EMT pipe and metal boxes (no rodents, horse damage).

I wired my shop and carriage barn in metal conduit. why not, its mine.

as far as bonding improvements with metal boxes go, you don't need to bond plastic, and the end result is that the outlet IS grounded, so the bonding is irrelevant.

also, as for the 1 gang vs 2 gang cost differences, im confused. i use whats called a 4 square box. its just a 4" x 4" open faced box with or without mounting flanges. cost about 1.10 here. then i can configure it for either a 1 gang or a 2 gang device by using a plaster ring (mud ring). the 1 gang costs the same as the 2 gang, about a buck. i get these at whatever depth the finish wall will be, 1/2", 5/8",etc.

i think you've been buying the 2 gang boxes with the device screws already attached....no one uses those. hence the high cost.

the boxes i use are available up to 8 gang configurations. i have included pics of the 4 square box with both covers, and also a picture of the expensive box i wont use. hope this helps

also, plastic boxes have a 2 hour fire rating. if the metal screws on the receptacle make contact with the metal box...BAMM, small explosion and tripped breaker. this is the reason to bond (ground) the metal box.

That's why you should wrap the side of the terminals with vinyl tape. I don't have this issue with plastic boxes. A commercial rated receptacle (about $4-6.00 each) have recessed screws to prevent shorting.

 

[JDgreen227]

I've used both. I prefer plastic. However, a couple years ago we smelled something bad on our enclosed porch. Investigation revealed some old wiring inside an outlet, with the duplex outlet melted into a puddle of goo and the wiring burnt to a crisp. The inside of the metal box had apparently contained and snuffed out a fire at some point. It appeared to be caused at the point where the wire was tightened under the screw terminal on the duplex outlet. I have to wonder if the metal in the box was able to resist the fire better than a plastic box might have. We dodged that bullet. Makes you wonder some times. That's all I'm sayin'.

MossRoad's comment about a metal box that contained a possible fire reminded me of what I found after I moved here about 20 years ago. The house I purchased was an Aladdin kit house, the majority of the outlet, switch, and junction boxes were ALUMINUM, not steel. The prior owner had hired an electrician to add new wall lights to the only bathroom, when I removed the original medicine cabinet, the pictures below are what I found on a stud wall by the cabinet. The four old black wires protruding from the sides are the 50 year old 14-2 house wires, the very bottom one on the left side is a newer Romex 14-2 with a ground spliced in, and the wire leading out the top is a single #14 that led to the basement cold water pipe. I have NEVER seen that method of grounding used before. Believe me, I am SO GLAD I found this junction box, I have NEVER seen anything so hazardous, the splices inside were taped, no wire nuts, and the box is only 2X3 inches. I took it out and have it hanging by my workbench as a reminder not to do careless work.

 

[grsthegreat]

MossRoad's comment about a metal box that contained a possible fire reminded me of what I found after I moved here about 20 years ago. The house I purchased was an Aladdin kit house, the majority of the outlet, switch, and junction boxes were ALUMINUM, not steel. The prior owner had hired an electrician to add new wall lights to the only bathroom, when I removed the original medicine cabinet, the pictures below are what I found on a stud wall by the cabinet. The four old black wires protruding from the sides are the 50 year old 14-2 house wires, the very bottom one on the left side is a newer Romex 14-2 with a ground spliced in, and the wire leading out the top is a single #14 that led to the basement cold water pipe. I have NEVER seen that method of grounding used before. Believe me, I am SO GLAD I found this junction box, I have NEVER seen anything so hazardous, the splices inside were taped, no wire nuts, and the box is only 2X3 inches. I took it out and have it hanging by my workbench as a reminder not to do careless work.

hmm, that has homeowner repair written all over it.

ive found some old work where someone ran a ground to some water pipe. absolutely useless. the ground HAS to run all the way back to the point of origin to allow stray voltage to make it back to the breaker and trip it.

that is one ugly picture there. In the old days, before wire nuts. people crimped the wires together and taped them.

 

[MossRoad]

hmm, that has homeowner repair written all over it.

Well, crud! There goes my cost savings! :laughing:

 

[JDgreen227]

Well, crud! There goes my cost savings! :laughing:

About ten years ago I was at a Home Depot, saw a guy there wearing a black T-shirt, on the back it had cartoons of stick figures, one if the figures was standing in front of a service panel getting a huge shock, the second was running down the street with his hair on fire, and a burning house in the background.

The front of the guy's shirt read:

"Electricity is not a hobby. Play it safe and
call XYZ Electric at 123-456-7890...."

I have been wiring and rewiring on my buildings for 24 years, can do just about anything but hookup to the service panel. Will work on sub panels if they are not energized. No way I could work on service panels for a living though.

 

[LD1]

My :2cents:

I like the plastic for ease of use.

No need IMO for a metal box for just recepticals and switches. Overhead stuff is different though.

Unlike a previous poster, I have had good luck with the blue boxes. I got them from menards, but I believe lowes and HD sell the exact same thing.

They are dirt cheap and I have yet to break one. Even when I have had to remove and re-position them. BUT the brownish fiberglass looking type I would avoid. They break very easily. They are almost TOO hard and brittle as a result.

I have also never seen the black ones, so I cant comment there. But I also buy the deeper boxes. More room for shovig the outlet back in. I like to leave at least enough wire in the box to be able to change and outlet or receptical if ever needed in the future. If you use a metal box with the retaining rings and dont leave much wire, you may be ripping out drywall in the future if a switch goes bad.

 

[studor]

If you are using boxes on the outside walls and are concerned about making the best seal possible in the insulated wall, then the plastic ones with the neoprene seals are definitely the way to go. Otherwise the metal box should be wrapped with plastic and sealed with caulking which is a PITA. Same goes with the ceiling below the attic if it is insulated.
For inside walls and lower level ceilings it does not really matter but I have always preferred the clamp arrangement in the metal boxes versus the plastic one but that is because the plastic ones tend to work well the first time then not so well after. I have also seen a number of metal nail on boxes that look like the were hit with a sledge hammer and the sides are barely holding on. Poor work can be done with plastic or metal-- JMHO

 

[boggen]

use both plastic and metal. on re-wiring house and sheds.

i tend to use metal boxes out in the shed, and also get metal face covers. for switches and outlets. this is mainly due to the face plats fit snug, and it is much hard to snag a sleeve or something on the edge of the box / face plate.

if there is going to be paneling or sheet rock or like on the wall. i will most likely go with a plastic box. due to they are cheaper, and gave a quick easy guide for how far the front of the box needs to stick out past the wall stud.

anything for ceiling = metal box.

the thing i hate about metal boxes. are the need for "plugs" more so out in the shed. when removing old metal boxes. i have found wasp nests, bee hives, and an arrangement of bugs and dust inside the boxes. just wrapping the box with tape does little good. that and the sheds are metal. so also dealing with a little drip or 2 here and there of water, from the metal sweating.

 

[grsthegreat]

About ten years ago I was at a Home Depot, saw a guy there wearing a black T-shirt, on the back it had cartoons of stick figures, one if the figures was standing in front of a service panel getting a huge shock, the second was running down the street with his hair on fire, and a burning house in the background.

The front of the guy's shirt read:

"Electricity is not a hobby. Play it safe and
call XYZ Electric at 123-456-7890...."

I have been wiring and rewiring on my buildings for 24 years, can do just about anything but hookup to the service panel. Will work on sub panels if they are not energized. No way I could work on service panels for a living though.

naaa, come on down. ill let you work in the live 6000 amp panels at the hospital i do work at....cant shut them down. work live with hot gloves, flash guards, and a prayer.

 

[Inspector507]

the very bottom one on the left side is a newer Romex 14-2 with a ground spliced in, and the wire leading out the top is a single #14 that led to the basement cold water pipe. I have NEVER seen that method of grounding used before.

ive found some old work where someone ran a ground to some water pipe. absolutely useless.

That was permitted by the NEC at one time. That was before it was common to use plastic water lines inside and underground as replacements.