Too Many Wires In Box - Code vs Practical Issue?

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  #1  
Old 04-26-07, 01:23 PM
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Too Many Wires In Box - Code vs Practical Issue?

I'm currently remodeling a small bathroom and have added a light/heater/fan unit and will also have switches for the vaity and shower light. For asthetic purposes I'd like to fit this all into a 2 gang box (I think a 3 gang would look huge in this bathroom). I have one of those 3 switch units and a matching 2 switch unit from Lowes.

Problem is, that's quite a few wires for a 2 gang box when all is said and done for the hot and switched sides. I've just dropped the wires thus far, but haven't begun putting them in the box.

4 x 12x2 ga Romex
2 x 14x2 ga Romex
1 x 12x3 ga Romex

A guy came by yesterday just to pick up some stuff I had for sale, and mentioned that I could do a 3 gang box to free up some room. I'm also picking up some deeper boxes to help out. The 3 gang sounded like a good idea, but I wasn't sure if that was to code, or if there would be any other unforeseen issues with using a 3 gang box but only putting a 2 gang cover on it. I presume i'd need to cut the side of the box back some.

Also, what is the practical limit of wires that can be placed in a 2 gang box...at least for someone of average skill. Any code limitations?
 
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  #2  
Old 04-26-07, 01:30 PM
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You cannot use a three gang box and place a two gang cover on it.

You have too many wires for a two gang box, and probably too many for a three gang boxes.

Redo your wiring to reduce the number of cables.
 
  #3  
Old 04-26-07, 01:51 PM
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Originally Posted by racraft View Post
You cannot use a three gang box and place a two gang cover on it.

You have too many wires for a two gang box, and probably too many for a three gang boxes.

Redo your wiring to reduce the number of cables.
I assume that's a code issue? The rest of the story was the "guy" who came over was an electrician, but I know contractors vary in knowledge.

How many wires are practical/legal for a two gang and three gang box? The electrician said 5 was about as much as he'd like, but these 2 and 3 switch units are also nearly as big as a GFCI on the back.

Can you expand on how I could reduce the number of wires short of just removing features or having switches all over this very small bath?

Thanks!
 
  #4  
Old 04-26-07, 01:55 PM
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You might want to consider running power to your light fixtures and then run switch loops to the switch. This will reduce the number of wires to your switch box.
 
  #5  
Old 04-26-07, 02:04 PM
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I would use nothing less than a 3 gang box. You would then use a 3 gang cover that allowed for the two devices and a blank section. You could do this with a 4 gang box and cover. You may not find the cover at the big box store but they are available.

Johny2050 makes a good point.

Not knowing how many different supply circuits there are it is difficult to state just how to reduce the number of wires. Again, what I would do is to install a junction box somewhere accessable (it doesn't need to be "readily accessable so in the attic or crawlspace is fine) and then run only the leads necessary to the switch location. I would most likely run flexible conduit between the switch box and the junction box and then run individual conductors. Assuming that the triple switch unit has one supply and three loads and the double switch unit has a separate (from the triple switch) supply and two loads that would be a totall of seven conductors between the switch location and the remote junction box.

I would use stranded THHN/THWN rated wire because the stranded wire is far easier to push back into the switch box.
 
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Old 04-26-07, 02:12 PM
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If this guy told you to use a certain number of wires without knowing the cubic inch capacity of the box, and/or if he told you to use a three gang box with a two gang cover...he is NO real electrician.

I have absolutely NO idea what he (the electrician) means by this:
"The electrician said 5 was about as much as he'd like, but these 2 and 3 switch units are also nearly as big as a GFCI on the back."


You need to do a REAL calculation as to how many wires you have and how many will fit into a certain box.
All plastic boxes are labeled with their capacity. DO NOT guess at this.

This is a code issue and also a practical issue. If the box is overfilled according to code you'll know it later when you go to put in the devices.
 
  #7  
Old 04-26-07, 02:40 PM
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The basics of box fill are as follows:

* each #12 wire entering the box requires 2.25 cu. in.
* each #14 wire entering the box requires 2 cu. in.
* each device (switch, receptacle) counts as two wires (4 or 4.5 cu. in.)
* all of the ground wires together count as one wire
* wire clamps count as one wire if they are not a moulded into the box
* wires which are contained within the box (pigtails) do not contribute to box fill

Every box should have a cubic inches measurement stamped on it somewhere. The sum of all the wire and device requirement should not exceed the cubic inches of the box. Note that an NM cable has three wires to consider in the fill calculation. Boxes cannot be cut, drilled or otherwise modified without violating their listing. All boxes must have a proper cover.

Box fill is important for two reasons. Cramped boxes will cause wires to be bent too hard and crack or damage wire insulation. There is also a possibility that over filled boxes can overheat.
 
  #8  
Old 04-26-07, 03:06 PM
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About the best I could do on a 2 gang was a 4-11/16" square, 2-1/8" deep box with a deep mud ring. You can get a mud ring up to about 1-1/2 or 2 inches deep. Then you just have to be careful to figure your wall covering depth so you can set the box properly. Mud rings in that size are stamped with their capacity.

I may be wrong , but you may be able to use an extension ring. You can get them for 4-11/16 and 4" square boxes. I don't recall if they are permitted to be concealed.

Also consider a 2 gang concrete box, although mounting may be a bit more challenging.

But I would go with the 3 gang. Put your devices on the ends and use a blank filler in the middle.

Also a good suggestion about using stranded. If you do that get backwire switches since they're much easier for stranded than side terminals.
 

Last edited by ArgMeMatey; 04-26-07 at 03:21 PM. Reason: Mention Ext Ring
  #9  
Old 04-26-07, 05:25 PM
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Thanks for all the replies!

The basic config is (and excuse any poor terminology):
Fan/Heat/Vent:
- 1 12x2 in, 1 12x3 and 1 12x2 out
Shower Light:
- 1 12x2 in, 1 14x2 out
Vanity Light:
- 1 12x2 in, 1 14x2 out

Wow, glad I wrote that out. I assume changing the hot side of the shower and vanity lights to 14x2 would be smart and make life easier.

johny2050: I haven't run any of those so I'd need to read up, but I presume they'd cut down one wire on each the shower light and vanity. Might not be a bad idea.

furd: I'll be using those "decorator" covers, and all I could find at Lowes was a triple with three openings. Any good source for one thats 3 wide with two openings, or just a good place to order oddball stuff? Great idea on the stranded wire! I'm betting that pushing it back in is where life will get tough.

ibpooks: Thanks for sharing the info (VERY helpful) that Petey should have if he was going to complain that much. The triple box I have is 52cubic inches. I'll swap out the hot sides to 14ga (unless anyone objects) for the shower/vanity, so here we go:

2 devices = 9cu
4 x 14x2ga = 24cu
2 x 12x2ga = 13.5cu
1 x 12x3 = 9cu
ground wires = 2.25cu (did I get that right?)
maybe 1 wire nut for grounds? = 2.25 (did I get that right?)
total = 60 (the original 2 gang was 34.5 and the current box is 52)

So, if I have that right I need to find an even larger box. No way I'm doing a 4 gang.

ArgMeMatey: Great idea on the big mud rings. I may be able to get away with a 2 gang that way (preferred), but I'll have to check to see if the big boxes even carry those rings. I have a few 50cu junction boxes around, so a deep mud ring would do the trick. My switches are all side mount, so the stranded idea may not work as well.

My favorite idea right now is swapping the hot sides of the vanity and shower lights back to 14ga, then using a 1" or so deep mud ring on a 4-11/16 junction box. Hopefully those rings can be concealed.
 
  #10  
Old 04-26-07, 05:52 PM
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It's not clear to me why you are mixing 12 and 14 AWG. Maybe I missed something above, but if it's a 20A circuit you must use all 12 AWG. If it's 15A you're going to do a lot of knuckle-skinning for no gain.

For that fan combo ... have you looked for 12-4 or 14-4? That would be White, Red, Black, Blue and Ground. Seems to me it exists but you may only find it at an electrical distributor such as Graybar, Badger, or Viking in these parts. Graybar will sell for cash, some others will not.

If I remember correctly, if you use a metal box for this you'll have to make sure the neutral and all the hots to the combo fan fixture exit thru the same hole in the box.

The big boxes have only the basics in 4-11/16", but a distributor will have just about whatever is manufactured.

I did my whole house in raceway & metal boxes, so I made a lot of trips to Graybar for special stuff.
 
  #11  
Old 04-26-07, 06:04 PM
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20A circuit, I just planned to use 14ga on the lights b/c they'de never pull anywhere near 15A.

The way the unit is designed, you'd need a 12x2 in one end and a 12x3 into the other. Kinda odd, but I'm just playing by the rules there.

Yep, it sounds like I'll be on the way to Greybar tomorrow. Right back near my old apartment in the days when I wondered why that place could sell anything..hehe.
 
  #12  
Old 04-26-07, 06:25 PM
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This is what I believe I'll need:
http://www.electrical-supply.net/product.asp_Q_parentID_E_414_A_subCatID_E_425_A_prodID_E_2348
 
  #13  
Old 04-26-07, 06:29 PM
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You cannot use #14 wire anywhere on a 20 Ampere circuit so forget that idea.

The big box stores are not the only places to purchase cover plates. There are probably a hundred different configurations of cover plates available that the boys and girls at the big box will tell you don't exist.

If you have a REAL hardware store in your area they may have the cover plates in stock; if not, they will special order them for you.

Since you are planning to go to Graybar anyway you can ask there for the cover plates.
 
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Old 04-26-07, 06:30 PM
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You MUST replace all that 14/2 with #12. That or change the breaker to 15 amp. Replacing the wire makes more sense.
It DOES NOT matter what the lights draw.

If you are using NM cable with wood framing there is NO good reason to use metal boxes.
 
  #15  
Old 04-26-07, 06:58 PM
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Good to know, I'll swap out the 14ga runs to 12ga...should be easy work at this stage.

I prefer metal boxes, so as long as there's no reason I MUST go plastic them we're doing metal here. I presume that's just your personal bias, right Petey.

furd: heck, Lowes doesn't carry light bulbs if you ask 30minutes before close. (BTW, I wish that was a joke)
 
  #16  
Old 04-26-07, 07:02 PM
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When mistakes are made with electrical installations, one may not know for several days, months or years.

People all the time say things like "i did it at my house and it is still standing."

Mistakes in electrical can lurk for years. then one day or night distroy your home.

Doing things per code and standard will only decrease your risk. but it is a substantial decrease.
 
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Old 04-26-07, 07:29 PM
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It really is just my preference to use plastic boxes. I personally have too many good reasons to use them, and actually no reason not to.

Like I said though. This is only for wood framing and NM cable.
 
  #18  
Old 04-26-07, 07:42 PM
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My reasons for metal is that I like using the metal wire retainers, but I guess a well-placed wire staple would be nearly as good in plastic. In this case, I'd also like the cavernous square shape of a 4-11/16 junction with 1.5" extension.

jwhite: That's why I'm here.
 
  #19  
Old 04-26-07, 07:50 PM
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Metal boxes generally have a smaller volume than their plastic counterparts, need to be grounded (a pain), need cable clamps, and are more expensive.
 
  #20  
Old 04-26-07, 09:40 PM
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Show me a 2 gang box with over 60cu in plastic and I'm all ears.
 
  #21  
Old 04-27-07, 05:05 AM
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I don't know where you are coming up with 60.

Six - 12/2 = 12
One - 12/3 = 3
All - grounds = 1
Two - devices = 4

12+3+1+4=20

20 x 2.25 = 45cu/in


I myself would find a different way to wire it.
 
  #22  
Old 04-27-07, 06:53 AM
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BQuicksilver, do yourself a favor and read up on switch loops. You will not need to go out and waste money on more supplies and jambing all those wires in a switch box, to me is a real PITA. From each switched fixture you will have one NM cable for that device to the switch box. Its pretty easy and you will know what to do if you ever run into another fixture when the white wire is connected to a black wire. Oh and what everyone else mentioned!! SAFETY SAFETY SAFTEY!!! Never mix wire gauge. It can confuse you and the next person working on that electrical system. A 15A circuit needs at least 14ga wire and 20A circuits needs a min of 12ga wire!!

I found a diagram of a switch loop to give you an idea of how it works. See link below!!

http://www.make-my-own-house.com/images/codedblackR.jpg
 

Last edited by johny2050; 04-27-07 at 06:57 AM. Reason: added link
  #23  
Old 04-27-07, 07:46 PM
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I've learned a TON in this thread! Thanks to everyone!!!

johny2050: That is a good idea. I think I'll do that, and I HAVE run into one before and wondered why that switch functioned with one wire.

The 14ga stuff is gone, no worries there.

I did get a 1" deep mud box for a 4-11/16 box, so between 2 fewer wires and a relatively large box, we should be in business.

Petey: I'm glad you checked my math since I hadn't done those calculations before..so you do not count the ground wires in NM cable? In other words a single 12x2 is 4.5cu, not 6.75cu? That's where my numbers differed.
 
  #24  
Old 04-28-07, 02:07 PM
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According to the guys who wote "wiring simplified" all the ground wires in a box count as one volume basing the volume on the largest ground wire in the box [good book, it's updated with each code revision and inepensive] . You might want to recheck the installation instructions for the heater/fan/light combo unit. I looked at the install document for a Nutone #665RP Heat-A-Ventlite Combonation online and it states that "the unit must be wired on a separate 120v, 20 amp circuit" [direct quote].
 
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