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Community and Q&A

Overpacked Electrical Outlets

moose_head27 | Posted in General Questions on

Hi I recently got some wiring roughed in my home. I’m located in Ontario, Canada. I have several receptacle boxes that seem like they are overloaded with wires? The boxes are 2x3x2.5 and the wire is 14-2. One box for example has 4 black, 4 white, 4 grounds, 3 merets and the 15 amp receptacle itself. Just looking at it, it seems wrong and there is no way that everything will fit or if it even passes code.

I’ve questioned the electrician about it several times. The first time prior to drywall, he says everything should fit in. The second time he says the job passed inspection. I’m looking to get a clear answer if its actually installed correct or its something thats being done and overlooked.

Would anyone be able to assist guiding me if this would pass in Ontario, or even your own jurisdiction?

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  1. Expert Member
    AKOS TOTH | | #1

    Yup, overfilled. Most should have been 5 wires and 3 marrettes. For box fill, ground wires don't count but insulated marrettes on them do.

    A 3" deep would have been close but still tad too small as it allows for 7 wires. The official solution would be a 3" box with a 1/2" extension.

    I'm surprised the inspector did not call them out on this.

    The PS Knight book is a good reference to keep around for these types of details, has a handy fill table for standard house boxes.

    1. moose_head27 | | #3

      The inspector was in my home for maybe 3 minutes. I didn't even have time to brew a pot of coffee and he was gone and passed the job. My 1000ft2 basement was roughed-in, I'd expect the inspector to be there for 20-30 minutes.

      Thank you for your information. Right now I really regret hiring this electrician. Other issues I found when drywalling was electrical wire too closely drilled to the inside studs. Some boxes weren't screwed in at the bottom and were lose. Seems like most switches aren't set at a set height, some are at 48, 51, 49 etc. Some boxes were side-by side, and wern't even level, one box was half an inch below. Smoke alarms boxes were installed on floor joists and not the strapping. The way he passed wires left no slack for the outlet boxes, everything seemed tight. Wires were passed over and under ductwork on the same ducts. No insulation was provided between the duct and wire that was in contact. Potlights weren't installed in the proper location as he designed.

      I more or less relied on the contractor and inspector to do their job. Some items are more cosmetic looking that I can live with. Some items we were able to correct when drywalling. I'm not sure if all the items are code issues in my jurisdiction but they did stand out to me based off the previous wiring that I've seen complete.

      1. Expert Member
        AKOS TOTH | | #5

        Overstuffed boxes are never a good idea.

        With a light switch it leaves you no room for a dimmer or any smart controls down the road.

        Outlets could have something like a space heater plugged in, add tight space and a number of wire connections and you are asking for trouble.

        For new wiring, I can't see any reason to accept either especially when it is code violation.

    2. this_page_left_blank | | #10

      Table 23 shows maximum 8 conductors in that box size. It's been a while, but I recall that each pair of wire nuts counts as one wire, rounding down. That would mean 7 conductors and three wire nuts is ok. Closer, but still over-filled.

  2. Expert Member
    BILL WICHERS | | #2

    I agree with Akos, that's a pretty full box.

    If you look closely at any electrical box, even a mudring, you'll see it marked with "cubic inches". This is the volume of the box (or the enclosed volume added to the box in the case of a mud ring). The code actually specifies how many cubic inches you need for every device, wire, and splice, and the boxes are marked so that you know what you have to work with in terms of available space.

    One of the ways to get around this problem in a residential box that has a lot going on is to use a 4" square box and a mud ring. This presents a single gang opening in the wall, but gives you the larger volume of the 4" square box to work with which is essentially a double gang box. You can also use "deep" boxes to gain space. It's very common in the commercial world to use 4" square boxes everywhere with mud rings for one or two devices as needed, but in the residential world you rarely see that.

    If the box passed inspection I wouldn't press the issue with the electrician. Mostly the electrician is making extra work for himself here, there isn't really much of a safety concern with this as long as the wires don't get damaged while they're being stuffed into the box. I would be extra careful that the screws on the device don't bite into any of the wires when you install the device. With plastic boxes this isn't usually a problem, but some metal boxes have the screw tab on the inside edge.


    1. moose_head27 | | #4

      Thanks Bill for the reply. The electrician will be back again and I'll be there. All the boxes were metal and I'm hoping there is no additional issues. I'll be taking a electrical course in the near future to get more knowledge of the trade and do my own work where I can.

    2. Expert Member
      MALCOLM TAYLOR | | #15


      "there isn't really much of a safety concern with this as long as the wires don't get damaged while they're being stuffed into the box."

      I thought fill limits were primarily to reduce the chance of overheating?

      1. Expert Member
        BILL WICHERS | | #16

        It's more to make sure things can fit than to deal with heating in this particular case. Heating is more of an issue in conduits containing multiple circuits (which is why there are rules about derating conductor ampacity for more than certain numbers of "current carrying" conductors in a single raceway or conduit). In things like boxes and panels, the issue is more to keep things from getting unmanageably stuffed to where risk of damaged wires increases.

        You probably won't be able to fit enough seperate current carrying wires in a box to significantly increase heating concerns there. There are also some exceptions for conduits for similar reasons (less than two feet long doesn't count for derating, for example). What does happen in boxes is you get to a point where the mounting wings on a receptacle or switch start to bend, the plate won't fit right, and the pressure can cause cold flow issues in the wire insulation. The screws biting into the wire problem I mentioned earlier is another issue. I've also seen wire nuts pop off from stress in some cases.


  3. Expert Member

    Electrical inspections here have become a joke. Ours now rely on the electrician submitting photos and videos. Things like box-fill don't get flagged. The quality and code adherence comes down to each electrician's competence. Your best bet is hiring an experienced, conscientious electrician.

    1. Expert Member
      BILL WICHERS | | #9

      We have that here too. The general rule is to make the panel look nice, and if you do, the inspector probably won't look too closely at anything else. There is one particular city that I know of here that I can talk to the inspector during the inspection and the guy gets distracted and doesn't pay attention. For me, inspections are more of a formality since I (as the consulting engineer) do my own inspections of my contractors, and I'm usually a lot more stringent than the city inspectors.

      At least they've started being more careful inspecting the structure after some well publicized structural failures in the past decade or so. I really hate seeing safety-related problems get missed. I can't count how many times I've been above a ceiling over a fire door and found someone smashed a hole through the fire wall with a hammer to run their little wire. I've seen wires run through automatic fire dampers too, which will prevent them from closing in time of fire. Those I always report to the building owners, typically along with my advice of "cut the wires, then yell at whomever complains about their stuff being broken prior to making them fix the wires so that they're safe".

      Cutting corners on construction projects can quite literally kill people, and it's really not something anyone should consider doing.


  4. tim_dilletante | | #7

    I'm not sure about Canada, but there is a formula for box fill in the NEC:
    It's not rocket science.

  5. walta100 | | #8

    Most boxes today have the answer to your question molded into the box.
    The box in my photo is a 32CU IN the chart says up to 16 #14s or 14 #12s, 12 #10s

    I would not make it a big deal if it was one or 2 boxes that are overfilled beyond that I might.


    1. this_page_left_blank | | #12

      Plastic boxes are not very common in Canada. The metal boxes often have the volume etched somewhere, but I've never seen one showing the number of allowable conductors. That's of very limited value anyway, because other factors affect the limit, including wire nuts and device size. For example, if you have a 1.5" deep GFCI outlet or dimmer switch, those numbers molded into the box go right out the window.

      1. Expert Member
        MALCOLM TAYLOR | | #13


        It must be a regional thing. I haven't seen a house here done in metal for decades.

  6. this_page_left_blank | | #11

    The maximum allowed for that size box is 8 conductors. As already mentioned, bare grounds don't count. If you get rid of the Marrettes, you'll be code compliant. How good is your soldering? You can replace the Marrettes with soldered connections covered in a few wraps of electrical tape, or better yet a couple of layers of CSA approved heat shrink tubing. That's for the conductors only. For the grounds you'd use a brass crimp nut, which also doesn't count as using any space. For reasons I've never been able to figure out (or been able to find anyone to explain), you can solder conductors, but not grounds.

    1. Expert Member
      BILL WICHERS | | #17

      I actually looked this up out of curiousity. 110.14(B) in the NEC says you can solder splices, and does not list any exceptions for grounds, which would imply soldered ground connections are OK. That's not to say there isn't some other exception elsewhere in the code (I checked the section on grounding and didn't see anything, but I don't have time to fully research this). I did find some references in some code forums that the code writers didn't trust the ability of everyone to make a good soldered connection, but nothing specific. It's possible newer codes allow soldered grounds.

      Personally I wouldn't solder smaller splices. It's too easy to damage the insulation while soldering, and soldering does take some skill to do properly. It's easy to get a poor electrical connection that looks good visually. Mechanical connections (wire nuts, etc.) are easier to do correctly without much experience.

      I'm not a big fan of the crimp rings since I've seen them loosen up too frequently. Wire nuts work by biting the wires in multiple places using a spring wound with square wire, so they tend to be pretty reliable ("Marrette" is just Canadian-speak for "Wire nut", and there is an interesting story behind why that is). For most DIYers, I would recommend a wire nut over other splice methods. I particularly like Ideal's "Wing nuts" because the larger "wings" make it easier to tighten them sufficiently. A properly tightened wire nut will make your finger just start to hurt a little while you're tightening. Be sure the skirt of the wirenut fully covers all exposed conductor areas in the case of wires other than the grounds too.


      1. this_page_left_blank | | #19

        It's possible that the restriction on soldering grounds is particular to the Canadian code.

        I think Marrette is just a ubiquitous brand name, kind of like Kleenex. Is there more to the story than that?

        The problem with "wing nuts" is they contribute to crowding problems in the box.

        I think you can't beat a solder connection for quality and space efficiency, but it definitely requires skill and is not for the average person.

        1. Expert Member
          MALCOLM TAYLOR | | #20


          Some residential electricians have started switching to lever nuts. They have been used in commercial projects for years, and have a few advantages over marrettes.

          1. Expert Member
            BILL WICHERS | | #21

            The generic name for those is usually a "push-in connector", at least South of the board :-) My crews have several different trade names for them though. While I still don't entirely trust them, I have only seen one failure so far, which is actually less than I've seen with wirenuts so I can't really say "they aren't as reliable" -- although wirenuts have been around a lot longer, so it will take some time to be sure.

            Trevor: "Marrette" was the name of the inventor of an early version of a wirenut, and he lived in Toronto. There is a little more to the history that I mentioned, but that's how Candians came to call "wirenuts" "Marrettes" -- they kept the original name of the Candian inventor of the first connector of the twist-on style. Before that guy had his "Aha!" moment of invention, electrical connections were usually soldered and taped. Tape fails over time, so the twist-on connectors are better, and also much faster to make connections with.

            BTW, has a side note, properly made crimp connectors are actually better than soldered connections. The US department of defense did research into that a long time ago, and there is a published report about it. A "properly made" crimp connection, which means using the correct tool for the connector in use, is a gas-tite connection (so no risk of oxidation), and it's less prone to brittle fracture failure over time compared with a soldered connection. It also takes little skill to make, provided you have the right tool.

            Lots of fun facts about some of the most basic part of electrical work today :-)


  7. Expert Member
    NICK KEENAN | | #14

    I had to Google "Marrette."

    I'd say this is a red flag. I wouldn't say that overstuffed junction boxes are a particular hazard, things tend to stay put once the lid is screwed on. It's more that this is an indicator that the guy doesn't know what he's doing. The wiring slows down a lot if you have more than two cables in a box, an experienced guy can look at a room and see right away how to run the wire so that each box has one cable in and one out. In renovation situations sometimes there's no avoiding a crowded junction box but not in new construction.

  8. drewintoledo | | #18

    Any chance of posting a photo of said box for reference as "what not to do"?

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