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  1. #1
    Super Member
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    4210 MFWD Ehydro--'89 JD 318

    Default Plastic or metal electrical boxes?

    I would be interested in learning which type of box the members here prefer for new construction...when we built on, my wifes's brother who is a journeyman electrician swore by those brownish-grey plastic boxes, saying they were the best type. But when I finished off and wired our basement, and rewired my barn, I used metal boxes. The issues I have with plastic boxes are that they are nail-on, and I think for most uses, they flex too much. I am very uncomfortable using them for ceiling light fixtures. I also hate it that when you push the wires back into the box after installing the switch or outlet, the wires flop around, while if you use a metal box you can use a cable clamp and eliminate that problem. Some people say "plastic boxes need no grounding" but I actually PREFER to have a grounded box.

    While on the issue, does anyone know why you can buy a square metal 4 inch junction box for a dollar, but a 2 gang metal switch box costs $6 or $7? Thanks.

    A footnote...I think plastic boxes were invented to speed up wiring, no wasting time screwing metal boxes to the framing, no need to ground the plastic ones, no messing with cable clamps...yeah, slap it together fast, as cheap as possible...

  2. #2
    Super Member clemsonfor's Avatar
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    Greenwood Co., SC
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    Yanmar YM2000

    Default Re: Plastic or metal electrical boxes?

    Quote Originally Posted by JDgreen227 View Post
    I would be interested in learning which type of box the members here prefer for new construction...when we built on, my wifes's brother who is a journeyman electrician swore by those brownish-grey plastic boxes, saying they were the best type. But when I finished off and wired our basement, and rewired my barn, I used metal boxes. The issues I have with plastic boxes are that they are nail-on, and I think for most uses, they flex too much. I am very uncomfortable using them for ceiling light fixtures. I also hate it that when you push the wires back into the box after installing the switch or outlet, the wires flop around, while if you use a metal box you can use a cable clamp and eliminate that problem. Some people say "plastic boxes need no grounding" but I actually PREFER to have a grounded box.

    While on the issue, does anyone know why you can buy a square metal 4 inch junction box for a dollar, but a 2 gang metal switch box costs $6 or $7? Thanks.

    A footnote...I think plastic boxes were invented to speed up wiring, no wasting time screwing metal boxes to the framing, no need to ground the plastic ones, no messing with cable clamps...yeah, slap it together fast, as cheap as possible...
    Ill give my thoughts for what there worth. I have rewired about 500 sqft of my house. It was built in the early to mid 50s, that part at least. I hate trying to get the hold down clamps in place, at least on my metal boxes. But on some new stuff ive done i have busted parts off of plastic easily, including the retaining tabs on the box.

    Again im no pro, what i know is from books and the internet and my own limited experience. But i think metal does not need grounding as it is grounded to the house as its is a conductor. They were uses with the old non grounded wire. The box is where the ground was. Plastic is non conductive so it needs the ground wire. Like they say electricity will take the path of least resistance, so if your going to arc its more likely to hit the metal box and go into the wall vs plastic faulty grounded going to you then ground.

    Overall i like plastic for the cheap and ease of things. Would i hang a 28lb ceiling fan off a $0.65 plastic box, probably not. But again those things have weight ratings on them so i guess as long as you stick to them you should be ok. Just a thought, the ceiling boxes will be in the hot attic, are these plastices that wont get brittle with age. Think 10-15 years and plastic that has been in the attic and how it can crumble?
    YM2000. MF dirt scoop,4' Jbar bushhog,boompole, LMC 12-16 disk harrow, 4' Atlas boxblade (with rippers). 1980 chevy K10,1990 ford ranger 2wd (285K miles),1997 saturn SL2 (twin cam!!),2001Toyota Higlander
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  3. #3
    Platinum Member Army grunt's Avatar
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    Georga
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    TC 30 Newholland

    Default Re: Plastic or metal electrical boxes?

    I use plastic boxes all the time, exept for cealing fixtures where a fan will be used or a hanging light. There fine, "IMO"
    Army Grunt
    "Be who you are, say what you will, those that matter wont mind, those that mind don't matter".

  4. #4
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    Branson 2400H

    Default Re: Plastic or metal electrical boxes?

    I don't believe electrical code will allow the use of plastic boxes for ceiling lights. I believe they must all be "fan" rated.

    Plastic outlet boxes: Use care when tightening the screws that hold the outlet or switch in. They crack or strip fairly easily. They are much quicker to wire since their is no pinch bolt/strain relief to mess with.

    Another problem with plastic boxes is the drywall crew can chew them up with their roto-zip. had an addition put on last summer and had two boxes covered by dry wall and two destroyed by drywall crew. Fortunately the contractor had to deal with it and not me.

    Plastic has its place, just question like others, how well it will hold up over time.

    Roy
    Artificial Intelligence will never overcome natural stupidity.

    Branson 2400H MMM & FEL

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  5. #5
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    Default Re: Plastic or metal electrical boxes?

    I usually use plastic boxes for normal outlets and switches, but metal boxes for ceiling lights and fans (usually use the specific-made fan boxes for fans). I've had good luck with plastic boxes - a fraction of the cost, quick to install, etc. I agree that once you get past a double-gang, the plastic is a little too flexible for my taste without being reinforced, and then you lose the economy that the plastic creates to start with, so in my opinion, metal is better for that.

    However, if someone doesn't like plastic boxes, the can spend their dollars any way they see fit and put in all metal and they'll never hear a complaint from me.

    Good luck and take care.

  6. #6
    Platinum Member
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    N.E. PA
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    BX22

    Default Re: Plastic or metal electrical boxes?

    I only use and prefer metal boxes. Did my house, additions, shed, etc all with metal. I just find that the metal box is more robust, and the clamps actually clamp. When pushing wires around and into the box to put the device in, the metal boxes are nice to have for the strength. I always use the 2.5" deep boxes to give me the most room in the box, to make things easy. Maybe overkill, but when you go back in a few years later to modify ot replace, it is nice to have the room.

    If cost is your issue, use plastic. If a more robust, quality job is a goal, go metal.

    paul

  7. #7
    Platinum Member eepete's Avatar
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    Default Re: Plastic or metal electrical boxes?

    When we did our house, I used metal boxes for outlets and plastic for the switches. Outlets get a lot of flexing as they get used, and I've had too many plastic boxes break at our old house. The switches get very little flexing. Only time will tell if the plastic in the boxes gets brittle and everyone discovers that at 50 years they start having problems.

    Another win of the metal for outlets is you can use washers and spacers to position the outlet correctly against the drywall. A lot of loose outlets use the drywall for support, and with time the drywall flexes or crumbles and the outlet is loose. With the washers, the outlet is supported just by the box and stud. Every outlet has a rock solid feel to it. Again, more time during installation and not something the trades would do.

    For the kitchen, there is a deep metal box that cost a lot ($3 or so?) but it is very good for the GFI breakers that are a too tight for "normal" outlet boxes. Instead of nails, I used 3.5" screws and put two pieces of shrink wrap on the screw where it was inside the box so that wires would not have the insulation cold flow into the sharp part of the screw. Best of all worlds, except for labor and to a much smaller degree cost of box. The down side is getting anyone in the construction business to do anything differently is a hurdle.

    Note also that using the big, screwed in metal box is a win if you can identify any outlet that will see a lot of use, such as vacuum cleaner or garage outlets.

    For ceiling boxes, I used metal. I put a 2x6 between the ceiling joists and screw the box into it. I messed up in the garage. I put in plastic boxes because I thought "I'll never put in a ceiling fan here". Well, 3 of them have broken where the screw for the fixture goes into them and it's been a pain retrofitting them with metal boxes. Live and learn.

    Also consider outlets in the halls. They are typically not required, but you can put these night lights in them. They are also great for vacuum cleaners. A few of these are in plastic boxes in areas where I know I would never use the outlet (we have central vacuum). Others are in the big metal boxes if they are in an area where they might get used. Here's a close up of the nightlight, and a pix of how it is used in the hall. The cat door is just a bonus, don't get me started...

    Pete
    Attached Thumbnails Attached Thumbnails -night_light_closeup-jpg   -night_light_hall-jpg  
    '09 JD4520 Cab (60HP), '97 KubotaB21 TLB (21HP), MX6 rotary mower, SB1106 6' Sickle Bar, BB3272 6' box blade, GradeMaster 7' Landplane, 6' landscape rake, Woods GTC 40" tiller, PHD 9" auger, 4' x 8' chain harrow, '90 JD318 (18HP gas) with 48" MM mower, 54" front blade, 47" snowblower.
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  8. #8
    Epic Contributor MossRoad's Avatar
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    Power Trac PT425 2001 Model Year

    Default Re: Plastic or metal electrical boxes?

    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

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  9. #9
    Super Member Mace Canute's Avatar
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    Default Re: Plastic or metal electrical boxes?

    Quote Originally Posted by clemsonfor View Post
    But i think metal does not need grounding as it is grounded to the house as its is a conductor. They were uses with the old non grounded wire. The box is where the ground was. Plastic is non conductive so it needs the ground wire. Like they say electricity will take the path of least resistance, so if your going to arc its more likely to hit the metal box and go into the wall vs plastic faulty grounded going to you then ground
    Metal boxes absolutely need to be grounded. The old wiring didn't have the ground wire so the outlets didn't have provisions for the ground prong - just hot and neutral and since there was no ground conductor in the wiring, the metal boxes at that time wouldn't have a provision to connect the ground wire to them. You absolutely can not expect a metal box to ground through the house! The house is absolutely NOT a conductor! A plastic box is non conductive. It does not need to be grounded, just the receptacle ground lug needs to be connected to the ground wire.
    Electricity does not take the path of least resistance, it takes the paths of all resistances. Every path is in parallel and the amount of current that flows depends on the individual resistance of each path.
    I don't think I have ever seen such dangerous statements concerning house wiring as yours are.

  10. #10
    Super Member
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    Default Re: Plastic or metal electrical boxes?

    Well stated, Mace...I hate to disagree with a poster who feels they are corrrect...thanks.

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