Plastic versus metal recep/switch boxes

[rinny_tin_tin]

OK - I'm certain this topic must have come up here before - but I'm a newbie.

I'm in the process of wiring my new 4-bay garage - so I'm bringing a 100A service from the house to the garage-- and now --I need receptacles and switch boxes, etc. So..I went to home depot and bought a case of the Blue Carlin Adjust-a-box singles, 6 doubles and 6 quads (New construction). However, and as expected, the guy at Home Depot didn't know squat about the boxes, and couldn't tell me how to terminate the cable through the rectangular knockouts. That is - what type of fastener is used to secure the cable, etc. Now - all my experience have been with metal boxes, and I know that the plastics are listed and all that, and that I don't have to ground the plastic boxes like I need to do with the metal, and firewise - the plastics will do as god as the metal since they are chlorinated, etc...but tell me - what has been your experience with these boxes, and should I take them back and use metal... etc!

 

[LoneGunman]

For Romex I prefer plastic boxes. The knockout is not a knockout like a panel knockout, meaning you do not remove it. Take your screwdriver, jab the piece of the knockout that's towards the front of the box, that will open that part up and the back part should still be connected. Once the wire is inserted you'll see how the knockout keeps the romex from being pulled out.

You will probably break some of the little plastic clips off, up to you if you still want to use them, I would as the wire will be stapled within 6" of the box so it will still be secure. I have also never heard of an inspector saying anything about the clips being broken off.

I prefer plastic because they do not rust, they are non conductive so you do not have to worry about the side of the energized receptacle arcing out against the box, they are less expensive, ETC.

 

[Junkman]

I have a older type plastic boxes in my home from when it was built, and newer type from when I had an addition added. I hate them with a passion. The retaining holes that the receptacle screws into stripped out on a few, and they were a real pain to fix. I only use metal boxes now, and this is the only thing that I used in my garage. In some instances, I had to replace the plastic boxes since they failed so miserably with metal boxes. That is an task that you don't want to get into. For the small additional cost, go with metal. If you were an electrician doing a job that every cent that you spent was coming out of your profits, you would be using plastic. If you were an electrician wiring your own home, you would be using metal. There is no substitute for quality metal...

 

[rinny_tin_tin]

Ok - gotcha - great - thanks -- so you like the plastics for Romex only..
Now - most all my branch circuits will use either 12-3 or 14-3 Type NM (Romex)

OK - now I see how the romex is kept into position, and like you say - since its stapled so close to the box, retention is not an issue - Thanks!

However, it makes sense from what you say that I best use metal if I use BX, MC, etc.

 

[tigmusky]

the brown plastic boxes are alot more stout. the blue ones ****!! IMO
Daye

 

[Kevin54]

the brown plastic boxes are alot more stout. the blue ones ****!! IMO
Daye

Why do they ****? Once they are in the wall and hidden, what is the matter with them. I like them. They have the small tab to locate depth for drywall, they nail on easy, they crimp the romex fine, and usually you can find them on sale for around $.25 apiece.

 

[LoneGunman]

"If you were an electrician wiring your own home, you would be using metal. There is no substitute for quality metal..."

The plastic threads are not exactly what I would consider stout but how ofter are you going to change devices once they are in? My house is plastic boxes, two guys from work who did their own electrical when they built also used plastic.

The garage is a different story, if I was to build a shop or garage I would not use plastic boxes because I would not be using romex, I'd be using conduit and 1900 (4 square) boxes. I'm not suggesting DIYer's use conduit, I'm only saying that's what I'd do but I can also can run EMT in my sleep.

 

[LoneGunman]

"However, it makes sense from what you say that I best use metal if I use BX, MC, etc."

As far as I know you could not use the plastic boxes for metal clad. I believe it's okay to use plastic junction boxes with EMT or RMC conduit if you use a bonding/grounding bushing to continue the ground. For some reason one of our guys used a PVC box when he had to tap into a section of 2" RMC, inspector passed it only upon the agreement that bonding bushings would be used.

 

[TRDon]

I am an electrician and I prefer plastic. Hvae the locate tabs, have nails ready to hit, dont have tpo ground the box. There are lots of advantaged to plastic over metal. The only metal I run is for pipe/mc/ac instalations. If you get the metal boxes, they are more expensive and you need the romex box adapters and ground screws or tails so it is more work. If you can get away with plastic, I say do it and save yourself a decent amout of money and time.

 

[79firebird]

For me when i have done some wireing for friends i would use plastic for inside a house as you dont plug and unplug stuff a lot. Where as in a shop how meany times do you plugin and unplug tools its a lot stronger

 

[ddawg16]

Most outstanding thread Garth........

NOW, this is what GJ is about.....ok, so not everyone agrees....but everyone explained why they like each type.......some very good info....

For me....plastic behind the wall....and assuming I'm not going to be messing with the wiring much if at all.

If the box is going to point towards the outside...I use metal....I want the strength because I'm going to have an outdoor hinged cover on it...

Good thread guys.

 

[Kevin54]

For me when i have done some wireing for friends i would use plastic for inside a house as you dont plug and unplug stuff a lot. Where as in a shop how meany times do you plugin and unplug tools its a lot stronger

I've plugged and unplugged cords hundreds of times and have never pulled an outlet loose from the box. If you pull one loose, then there is another problem other than the box.

 

[shocksystems]

I used plastic boxes in my garage. There are different quality blue boxes. I used a combination of the cheapies and the nicer adjustable ones. I wish I had done all of them with the nicer ones. Spend the extra money if you use the plastic ones. The good ones had the adjuster screw to set the depth of the box (I think that is what you described you bought) and you actually fasten the metal bracket to the face of the stud as I recall.

My biggest complaint about the plastic boxes is that you have to be careful to retain their shape. Particularly if you use the boxes for two receptacles. I have several that after nailing the cheap ones to the stud the box was no longer perfectly square. Another annoyance is what Junk describes, the screw holes, by their nature being plastic, do not have strong threads.

I like the metal boxes much more. Everything about them screams higher quality. Everything residential seems to have gone plastic now though.

Good luck whichever way you go.

Cheers!

Jim

 

[BigChevy80]

If it's going to be recessed inside the wall, I like plastic. I've never once had a problem with the newer blue boxes stripping threads. Some older existing plastic boxes have given me trouble in the past, but they were from the 80's.

If the boxes are going to be exposed, I'll use metal and EMT. I did it this way in my garage.

 

[MisterCMK]

Another option to look into is fiberglass boxes...

 

[MisterCMK]

Oh and putting a pipe down into a wall without any end on it and then going into a blue plastic box with THHN for a 277v light circuit is a no no. I was re-wiring the lights at out shop and found a little jewel like that behind the wall. WTF were people thinking.

 

[rinny_tin_tin]

Oh and putting a pipe down into a wall without any end on it and then going into a blue plastic box with THHN for a 277v light circuit is a no no. I was re-wiring the lights at out shop and found a little jewel like that behind the wall. WTF were people thinking.

Not that I would do that - but why is that wrong? Is it a NEC or Building Code violation? The blue plastic boxes are rated for 600V..so 277 V should be no problem...you would think

 

[rinny_tin_tin]

OK... what I have heard so far seems balanced and doesn't sway me one way or another - however, appears more positive than negative for the plastic. On the one hand, the {newer} plastic boxes are fine, except for some concerns expressed regarding the holding power of the molded screw feature. However, I have had some problems with some (although admittedly limited) with the threaded screw feature (what is it - 10-24, 8-32, whatever) on some metal boxes. Also, there is some concern expressed for the plug holding or retention in the wall performance for applications where plugs are put in and withdrawn relatively frequently. But...the number/quality of fasteners for the metal boxes appear to me to be about the same as for the plastic.

Bear in mind...that my intuition and my own experience has me biased against the plastic boxes; however, I can't explain why. So far, from the opinions expressed herein, the responses seem more positive than negative for plastic -- however, I tend to agree with some of the opinion that extreme duty applications would be better served with the metal - but again, a solid basis has not yet surfaced.

 

[2LTim]

My house is all blue plastic and romex, the shop is all metal, EMT and stranded copper!

 

[walrus]

Not that I would do that - but why is that wrong? Is it a NEC or Building Code violation? The blue plastic boxes are rated for 600V..so 277 V should be no problem...you would think

He said the conduit had no end on it so I'm assuming it wasn't connected to the box.

 

[tfi racing]

My preference is metal,but that is probably just a bias because that is all I ever really had experience with,and in Alberta that was the predominant box type.In this area of BC,it seems the plastic boxes are the choice of most residential contractors,perhaps because you don't have to use a separate vapour hat with them on your exterior walls.I'm going to use metal boxes on my new garage,mostly because I still have a bunch of boxes and hats from my contracting days.

 

[FakeName]

Thanks all, for a lot of info.

I may be using shop lights that have a 6' BX pigtail. Can I use that pigtail into a plastic box? Or should I run romex supply to metal boxes?

And, since I have the attention of experts here- I may be using a suspended ceiling- can I use romex up there? The only other suspended ceilings I've seen were in commercial buildings and it was all flex/bx.

Thanks again.

 

[2LTim]

Hold the phone guys! What are you talking about the "Threads" in the plastics? There are no threads in the plastic boxes until you put the screws in for the first time. If you manage to get it cross ways for the first half I could see it being weak, but beyond that, a 1/4 inch of screw properly inserted into plastic holds as well if not better than 3/32 of an inch into metal. If you want to Conan the screws in with a drill, I have seen more stripping occur in metal, albeit it's usually the screw threads that let go, and then you have a hell of a time getting it back out.

 

[LoneGunman]

Thanks all, for a lot of info.

I may be using shop lights that have a 6' BX pigtail. Can I use that pigtail into a plastic box? Or should I run romex supply to metal boxes?

And, since I have the attention of experts here- I may be using a suspended ceiling- can I use romex up there? The only other suspended ceilings I've seen were in commercial buildings and it was all flex/bx.

Thanks again.

The pig tails should terminate inside of a 1900 (4 square) box, which is a metal box. Romex is fine in the drop ceiling in your application, it must be supported, not just lying on the ceiling grid.

 

[FakeName]

The pig tails should terminate inside of a 1900 (4 square) box, which is a metal box. Romex is fine in the drop ceiling in your application, it must be supported, not just lying on the ceiling grid.

Thank you!

fn

 

[buening]

I've had horrible luck with plastic boxes in the ceiling for lights and ceiling fans. The weight from the fixture breaks the ears off the boxes and the box now rests against the drywall. The contractor used yellow colored boxes, and they are extremely fragile. I put metal ceiling boxes on the ones I could access from the attic. This is on my two-story house. For wall outlets in the garage I used plastic boxes.

 

[LoneGunman]

I've had horrible luck with plastic boxes in the ceiling for lights and ceiling fans. The weight from the fixture breaks the ears off the boxes and the box now rests against the drywall. The contractor used yellow colored boxes, and they are extremely fragile. I put metal ceiling boxes on the ones I could access from the attic. This is on my two-story house. For wall outlets in the garage I used plastic boxes.

From what you have said it does not sound like you have fan rated boxes.

 

[buening]

Thats highly possible. They sure are now!!!

 

[BigChevy80]

From what you have said it does not sound like you have fan rated boxes.

When hanging a fan, I always nail a sideways 2x4 between the joists and screw the box to that. I don't really trust those fan boxes with the metal arm on the back...

 

[TRDon]

I've had horrible luck with plastic boxes in the ceiling for lights and ceiling fans. The weight from the fixture breaks the ears off the boxes and the box now rests against the drywall. The contractor used yellow colored boxes, and they are extremely fragile. I put metal ceiling boxes on the ones I could access from the attic. This is on my two-story house. For wall outlets in the garage I used plastic boxes.

That because you used the wrong box for the fan. I always use metal, but correct me if I am wrong, but it seems that you used a old work cut in type box to mount your fan. If that is the case, that is a mojor no-no.

 

[buening]

I didn't use the wrong box, as I didn't build the house. Whoever the electrician was may have used the wrong one. It was a yellow ceiling box that has two nails at 45° going into the same joist. I put the correct metal ones in now, so no broken ears

 

[MisterCMK]

Not that I would do that - but why is that wrong? Is it a NEC or Building Code violation? The blue plastic boxes are rated for 600V..so 277 V should be no problem...you would think

He said the conduit had no end on it so I'm assuming it wasn't connected to the box.

Exactly. The thhn came out of the end of the conduit (which had no bushing or anything on the end of it) for about 6-8" and then it went into the blue plastic box. I have since fixed it with a couple of handy boxes ganged together but I was somewhat surprised to see that in the wall.

 

[MisterCMK]

I actually remembered to take a picture of it too.

 

[LoneGunman]

When hanging a fan, I always nail a sideways 2x4 between the joists and screw the box to that. I don't really trust those fan boxes with the metal arm on the back...

Try doing that on a remodel with no attic access Anyway, you only see the bat boxes when the fan is added later because they are way to expensive to use on new construction plus theres just no reason to use them. 99% of the new construction fan boxes are the ones that are steel and mount directly to a stud with the 4 provided little lags.

 

[rinny_tin_tin]

OK - From what appears to be the consensus here:

Plastic is OK for routine/random use switchboxes/receptacles

Plastic may not be OK for ceiling/overhead applications

Even with metal, overhead/ceiling arrangements holding any weight should
assess supplementary supporting means, and not just rely on attached arms,etc

Metal is preferred overall, but is a bigger pain during install

Metal is preferred for extreme use,particularly when exposed in industrial/commercial settings

Plastic is OK for Type NM, but not necessarily for other types, such as MC, and others where the integral strain relief system may be problematic


All useful info ! I'm going to take the consensus recommendations above to heart - so I have decided to go with a hybrid arrangement where I use both plastic and metal to comply with the aforementioned. I'll use plastic for routine use 15/20 A 120V applications, entry switches, undedicated utility receptacles, or dedicated recep where plug/in plug out use is not a requirement (e.g., garage door opener, retractable power reel, etc) Metal shall be used where plug/in - plug/out is typical, 220V service and/or any service over 20A and in all cases where branch cable is not NM, and in overhead/ceiling applications, and in all applications where expected to hold a weight of 10 lbs or over, or where used in harsh environment subject to
physical abuse.

Wish I could put this all in one sentence of 25 words or less! Anyone want to try?

 

[LoneGunman]

I actually remembered to take a picture of it too.

LOL, I have seen that probably a dozen times in 15 years, handyman or homeowner.

 

[W-Cummins]

The one reason I HATE the light weight blue boxes has nothing to do with any electrical requirements. I hate them because I like to use a roto-zip tool to cut out the drywall and I also like 5/8" drywall. The dam cutter cuts through the side if the blue plastic box like it's not there... And unless your VERY carefull makes a mess....

William....

 

[2LTim]

"The one reason I HATE the light weight blue boxes has nothing to do with any electrical requirements. I hate them because I like to use a roto-zip tool to cut out the drywall and I also like 5/8" drywall. The dam cutter cuts through the side if the blue plastic box like it's not there... And unless your VERY carefull makes a mess....

William...."

Ever try a pilot tip roto zip blade? This is also a great place to insert my brother-in-laws favorite saying, "That's why mud comes in five gallon buckets!"


"Wish I could put this all in one sentence of 25 words or less! Anyone want to try?"
rinny tin tin
How about this, "I will use what I like and what I am comfortable with...... If you don't like it, TUFF!!"

 

[rinny_tin_tin]

"The one reason I HATE the light weight blue boxes has nothing to do with any electrical requirements. I hate them because I like to use a roto-zip tool to cut out the drywall and I also like 5/8" drywall. The dam cutter cuts through the side if the blue plastic box like it's not there... And unless your VERY carefull makes a mess....

William...."

Ever try a pilot tip roto zip blade? This is also a great place to insert my brother-in-laws favorite saying, "That's why mud comes in five gallon buckets!"


"Wish I could put this all in one sentence of 25 words or less! Anyone want to try?"
rinny tin tin
How about this, "I will use what I like and what I am comfortable with...... If you don't like it, TUFF!!"

Bravo - and you used all of 18 words. Now I need to shake off the goose pimples.

 

[BigChevy80]

The one reason I HATE the light weight blue boxes has nothing to do with any electrical requirements. I hate them because I like to use a roto-zip tool to cut out the drywall and I also like 5/8" drywall. The dam cutter cuts through the side if the blue plastic box like it's not there... And unless your VERY carefull makes a mess....

William....

Trace the box onto the wall with a pencil and THEN cut the hole.