Plastic Boxes on Commercial Jobs

James L

Senior Member
If I missed something already stated, forgive me:

If it's a metal stud job, I would think you would be forced to use metal boxes.
I would think the non metallic boxes would be assumed with NM cable.

If it were metal studs and romex, no problem. There are plastic bushings to fit punched holes, plastic cable stackers that come with tek screws, and Pass & Seymour makes plastic boxes that come with Tek screws.
 

tkb

Senior Member
I would think the non metallic boxes would be assumed with NM cable.

If it were metal studs and romex, no problem. There are plastic bushings to fit punched holes, plastic cable stackers that come with tek screws, and Pass & Seymour makes plastic boxes that come with Tek screws.
Why would it be assumed to be plastic boxes when it was specked to be metal boxes?
If metal boxes were specified, then metal boxes should have been included in the bid pricing unless it was negotiated during bid time.
 

JFletcher

Senior Member
If I missed something already stated, forgive me:

If it's a metal stud job, I would think you would be forced to use metal boxes.
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ofc those are no good if it's double layered drywall

and kwired, I know Ive seen 2hr plastic boxes, just not sure *all* of them are two hour.

quick code question that's off topic: when doing old work with 2 wire cloth NM, can one use a metal box anymore?
 

luckylerado

Senior Member
I have yet to hear any logical reason to use a metal box at 10 times the cost where a plastic box would otherwise be acceptable other than to say it was in the spec which is not the point I am trying to understand.

Someone please lay it out there for me because I am truly stumped.
 

James L

Senior Member
Why would it be assumed to be plastic boxes when it was specked to be metal boxes?
If metal boxes were specified, then metal boxes should have been included in the bid pricing unless it was negotiated during bid time.
Conduit/mc was spec'd also. But NM was approved as a substitute.

Any rational mind would probably understand that metal boxes go hand in hand with conduit/mc and non-metallic boxes go hand in hand with non-metallic cable

From Allied Moulded website - 1098 single gang box:

"Single gang electrical box for use with nonmetallic sheathed cable"

Granted, it also says they're for residential use - which is another instance of various parameters going hand in hand:
residential, NM cable, nm boxes
commercial, EMT/ MC, metallic boxes

2 of the 3 parameters are already out of the perceived norm. The third would be assumed in my mind

Like I wrote on page 1, a lot of the stuff in the general notes on a set of prints is nothing but stock filler jargon that means absolutely nothing to the engineer or architect.

Somebody just didn't find it necessary to go into every trivial detail when NM cable got approved as a substitute, they probably gave no thought at all to the boxes.
 

mwm1752

Senior Member
Conduit/mc was spec'd also. But NM was approved as a substitute.

Any rational mind would probably understand that metal boxes go hand in hand with conduit/mc and non-metallic boxes go hand in hand with non-metallic cable

From Allied Moulded website - 1098 single gang box:

"Single gang electrical box for use with nonmetallic sheathed cable"

Granted, it also says they're for residential use - which is another instance of various parameters going hand in hand:
residential, NM cable, nm boxes
commercial, EMT/ MC, metallic boxes

2 of the 3 parameters are already out of the perceived norm. The third would be assumed in my mind

Like I wrote on page 1, a lot of the stuff in the general notes on a set of prints is nothing but stock filler jargon that means absolutely nothing to the engineer or architect.

Somebody just didn't find it necessary to go into every trivial detail when NM cable got approved as a substitute, they probably gave no thought at all to the boxes.
You said it NM was approved as asubstitute so since the approved plans called for metal boxes get an approved substitute. KISS. You know what assume means right? It would be no difference when an engineer wants all 20 amp home runs as a 10# wire, he takes responsibility for the reason & install per design. NEC does not regulate voltage drop but has FPN on it. Certainly an easy miss by the inspector that doesn't review. The inspector may not be liable for inspecting to the NEC only when the plans are above & beyond its scope. The Inspectors job should also promote assisting the EC with information he may have missed.
As for the us in a commercial setting 314.3 describes the wiring methods non metallic boxes can be usde with.
 

don_resqcapt19

Moderator
Staff member
I have yet to hear any logical reason to use a metal box at 10 times the cost where a plastic box would otherwise be acceptable other than to say it was in the spec which is not the point I am trying to understand.

Someone please lay it out there for me because I am truly stumped.
One of the reasons around here is too many got red-tagged for box fill when using single gang plastic boxes and they discovered that issue mostly goes away with a 4 square and plaster ring....they are too lazy or don't know how to do the box fill calculation.

Sure you can get the a plastic box with the correct volume, but you have to understand 314.16 to do that.
 

don_resqcapt19

Moderator
Staff member
....
Like I wrote on page 1, a lot of the stuff in the general notes on a set of prints is nothing but stock filler jargon that means absolutely nothing to the engineer or architect.

Somebody just didn't find it necessary to go into every trivial detail when NM cable got approved as a substitute, they probably gave no thought at all to the boxes.
That is fine as long as you get away with it, but it could be a huge cost issue if the engineer catches it on the final walk through and tells you that you have to comply with the contract documents.

I would never make that type of change without something in writing before making the change.

We had a job where the documents required solid for all conductors #10 and smaller....we never use solid #10, and used stranded. We had to pull it out and replace it with solid to get our final payment.
 

Frank DuVal

Senior Member
The plastic boxes are made for easy conductor fill calculations, as everyone I have used has the number of 10s, 12s or 14s can be in the box! Of course if you are mixing wire sizes, then you actually might have to do math.

Metal studs, plastic boxes and variable depth drywall? Surely you have seen the Arlington ads with the adjustable boxes. They screw right to metal studs.

Frank DuVal
 

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tkb

Senior Member
Really, Why can't you use plastic romex boxes ,NM and plastic bushings with metal studs. (not speaking of this project)
You could, but if the project was specified with metal boxes, the customer is paying for metal boxes. If they are substituted with plastic boxes then the customer is getting a lower quality product and paying for a higher quality product.

This is the same as bait and switch. Steeling from the customer since you are being paid for the higher quality product.
 

luckylerado

Senior Member
....the customer is getting a lower quality product and paying for a higher quality product....
This is where you lose me. What makes metal boxes higher quality? It is opinion only. Where is any evidence that this is true.

I agree with your comments on spec. It would be my strategy from the GC perspective to put that in my pocket and use it to negotiate issues later on down the road if I had to.

It works both ways
 
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luckylerado

Senior Member
For those advocating for metal boxes, do you use the plastic NM connectors or the threaded lock-nut / set-screw type?
 

tkb

Senior Member
This is where you lose me. What makes metal boxes higher quality? It is opinion only. Where is any evidence that this is true.

I agree with your comments on spec. It would be my strategy from the GC perspective to put that in my pocket and use it to negotiate issues later on down the road if I had to.

It works both ways
I don't understand your confusion. When you hold a plastic box and a metal box in your hand the quality difference is evident.
You can crush a plastic box in your hand. Try that with a metal box.
Also I have seen hundreds of plastic boxed deformed after walls were drywalled, not so with metal boxes.
Then there is the stripped out device mounting holes in the plastic boxes that happen often.

How can you say that there is no quality difference. Tell me how the plastic boxes are superior.
 

tkb

Senior Member
There is also a problem with plastic boxes being set to be flush with the finished surface to meet code. With metal boxes you can use a variety of different depth plaster rings.

Most plastic boxes cannot be set any different than their bracket will allow unless you get the more expensive adjustable box or spend more time mounting. This negates the cost savings of the plastic boxes over metal.

The substitution of metal boxes with plastic when metal is specified without approval is a scumbag maneuver by irreputable contractors.
 

luckylerado

Senior Member
I don't understand your confusion. When you hold a plastic box and a metal box in your hand the quality difference is evident.
You can crush a plastic box in your hand. Try that with a metal box.
Also I have seen hundreds of plastic boxed deformed after walls were drywalled, not so with metal boxes.
Then there is the stripped out device mounting holes in the plastic boxes that happen often.

How can you say that there is no quality difference. Tell me how the plastic boxes are superior.
Oh balderdash. You are not crushing plastic boxes with your hand Andre. If your are using bakelite / fiber boxes I might bite I guess but I still have my doubts. For every deformed box you have seen I have seen a mud ring installed crooked and for every stripped out plastic device hole there is a stripped out or broken metal tab or worse a device screw with the head snapped off. As for depth, if you get the right stuff for the task and know how to use the little hash marks on the box you are good to go. Your scumbag coment seems a little harsh. This didn't sound like a bait and switch.

Lighter, Cheaper, Faster, generally easier to install, generally requires no additional hardware or brackets, does not require connectors, mudrings or EGC connection, fire rated, marked with fill for common branch circuit conductors are all reasons to think plastic boxes are superior in the scenario described here.
 

Sierrasparky

Senior Member
The substitution of metal boxes with plastic when metal is specified without approval is a scumbag maneuver by irreputable contractors.
That is a bit harsh.

You could, but if the project was specified with metal boxes, the customer is paying for metal boxes. If they are substituted with plastic boxes then the customer is getting a lower quality product and paying for a higher quality product.

This is the same as bait and switch. Steeling from the customer since you are being paid for the higher quality product.
On a technical note the OP states the project was spec'd for MC and EMT and was Quality engineered for NM.

If I were that EC I would argue that the change to go NM came will all the NM methods used for this type of wiring. Would you expect to see Heavy duty one hole straps be used if that was the original plan before the Value engineering took place. Or if the plan spec'd all switch legs to be "Purple" sounds ridiculous doesn't it

Conduit/mc was spec'd also. But NM was approved as a substitute.

Any rational mind would probably understand that metal boxes go hand in hand with conduit/mc and non-metallic boxes go hand in hand with non-metallic cable

From Allied Moulded website - 1098 single gang box:

"Single gang electrical box for use with nonmetallic sheathed cable"

Granted, it also says they're for residential use - which is another instance of various parameters going hand in hand:
residential, NM cable, nm boxes
commercial, EMT/ MC, metallic boxes

2 of the 3 parameters are already out of the perceived norm. The third would be assumed in my mind

Like I wrote on page 1, a lot of the stuff in the general notes on a set of prints is nothing but stock filler jargon that means absolutely nothing to the engineer or architect.

Somebody just didn't find it necessary to go into every trivial detail when NM cable got approved as a substitute, they probably gave no thought at all to the boxes.
Agreed!
 

kwired

Electron manager
One of the reasons around here is too many got red-tagged for box fill when using single gang plastic boxes and they discovered that issue mostly goes away with a 4 square and plaster ring....they are too lazy or don't know how to do the box fill calculation.

Sure you can get the a plastic box with the correct volume, but you have to understand 314.16 to do that.
You have to break down and get a few of the 40 cent boxes where more fill is needed and not just buying the 25 cent boxes only for the entire project. Need more volume yet, there are plastic or fiberglass 4x4's and mud rings - some even with integral cable clamps.

You could, but if the project was specified with metal boxes, the customer is paying for metal boxes. If they are substituted with plastic boxes then the customer is getting a lower quality product and paying for a higher quality product.

This is the same as bait and switch. Steeling from the customer since you are being paid for the higher quality product.
OP situation makes more sense since he later posted that it was requested and approved to switch wiring method to NM cable - I myself would have assumed that switching to NM cable likely includes switching to boxes and other items more commonly used with NM cable. I guess from now on I will try to remember to ask about more then just the cable if ever in such a situation, just in case.
 
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