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This question comes from Shirlock's comment on this GFCI wiring question.

When and why should you use the holes on the back of an outlet rather than the side terminals? I always assumed the holes on the back were only for lazy electricians and people that wanted to make my life miserable, especially when there isn't much slack wire and you want to replace an outlet. Are there other reasons, and does the NEC have any requirements on one vs the other?

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Holes in the back were news to me...my sore hands would love an answer. –  user7116 Jul 31 '11 at 0:26
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@six: BYW, a good pair of diagonal cutters (dikes) makes easy work of making curls in 12 and 14 AWG solid wire. Use the curve of the back or the blades to make a nice "C" by grabbing the end of the bare wire in the cutter blade, squeeze gently and roll the wire around the back of the jaws ( blades). –  shirlock homes Jul 31 '11 at 1:04
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3 Answers 3

up vote 11 down vote accepted

There are no NEC guides, UL and CSA rules on or approves devices. The reason I commented on using back wiring on GFI's, is that if you look carefully inside the holes, you will see a barbed plate that compresses on the wire when the side screw is tightened. You will also notice because the devise itself is very wide, there is little barrier space around the screws. Most manufacturers recommend using the strip gage and back wiring holes. Just be sure to tip the device so the grab plates open before inserting the wires. Every electrician I know, uses the back connections on GFI's and side wires regular receptacles. Also notice that there are holes for 4 pairs of wires, two pairs for line side and two pairs for load side. Again, this saves room in the box so less wirenuts and splices need to be used.

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Interesting, so it's just space saving and the fact that the screws clamp in the wire (rather than friction) and not a safety concern with water leakage. Thanks Shirlock, I'm still learning something new everyday. –  BMitch Jul 31 '11 at 1:05
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"Every electrician I know, uses the back connections on GFI's and side wires regular receptacles." Although this may be true, every house I have torn into in order to replace receptacles has used the back holes for everything. –  Kellenjb Aug 3 '11 at 1:40
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@kellenjb: that is because they are just trying to cut time. Good electricians side wire regular recpts –  shirlock homes Sep 13 '11 at 23:35
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And I've lived in houses where those back push-in connections have relaxed, and have removed the charred plastic that results. As an end socket maybe, but as the first socket in a daisy chain? Potential future fire hazard. Most sockets nowdays have side clamp (straight wire) plates underneath the screw. Use those, not the push-ins. –  Fiasco Labs Jul 9 '13 at 17:17
    
You can get regular outlets and switches with the same style of connection as GFCIs. You can also get GFCIs that only have a screw connection. –  Brad Gilbert Oct 11 '13 at 1:03
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I have had multiple experiences that have had the push-in lose their connection, and the solution was to change it to use the side screws. For that reason I recommend always using the screws.

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If you look at the warnings on those things carefully, they specifically tell you not to reuse the QuickWire clamps. Once you've inserted and released a wire once, you're side-wiring; that's a major reason they're pretty much gone in new switches. –  KeithS Jun 17 at 0:47
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Shirlock has a great answer; I just wanted to point out something. There are two major different designs for back-wiring, "push-in" and "side-clamp".

Push-in wiring, sometimes branded "QuickWire", uses holes in the plastic casing, underneath which are sharp spring-loaded cleats that catch and hold the wire when you put it in. To remove them, you take a jeweler's screwdriver or a small pick or probe and push into a square tab nearby, which pushes the cleat away allowing you to withdraw the wire. Personally, I hate these things with a passion and prefer to side-wire. They only work with one gauge of wire (either 12 or 14AWG depending on the type of switch or outlet; do YOU know which one was used in every single J-box in your home?), and getting the wire back out without destroying the wire or the switch is a crap shoot. The push-release mechanism is as likely to crumple and lock the wire in as to release it, IME.

Side-clamp wiring uses a plate between the side-wiring screw and the switch body. You loosen the screw, separate the plate from the switch body (easiest to let gravity do the work; turn it plate-down and shake), insert the wire stripped to the proper length, then tighten down the side screw. It works a lot like side-wiring, except you don't have to curl the wire around the screw. They're pretty easy to use and are VERY secure, and so I like these a lot better than the push-in wiring setups. The only possible problem is, with a lot of exposed metal on the side of the switch body, you have to be certain you don't short out the switch to the bare metal ground wire, or the next switch or outlet over (very easy with the wider 20A switches and GFCI outlets). I did that a few times while repairing the electrical in my new home; the switch or plug worked fine hanging loose, but when I closed it up it stopped working. The fail-safe is to give the switch body a wrap of electrical tape, giving it an insulating layer between the switch and anything else in the box (and the box itself; most are plastic but I found a couple conductive switch/outlet J-boxes in my home).

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Good explanation of exactly what I was referring to. I always wrap devices with 33+ electrical tape in mult-device or metal boxes. If I ever have to release a friction back wired device, I replace it or only side wire it, never try to reuse the back push-in hole connector. +vote –  shirlock homes Aug 1 '11 at 21:34
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Using electrical tape to protect against a short like that is asking for trouble - if there is any physical contact, you won't know it when you close the box. It will eventually wear (movement through plug insertion/removal, shifting, thermal expansion/contraction, piercing from pressure - and tape is a soft material), then you'll have arcing in your box - a good recipe for a fire. Better off to know you have an issue, and fix it with physical separation, than patch it. –  user13909 Jul 9 '13 at 16:34
    
... I might agree, but with these wider 20A or GCFI node bodies that are the case in point, there's usually very little wiggle room and so physical separation isn't possible. I've never closed up a box with any two switches or plugs visibly touching, but I don't think it's a bad idea to give the switch a wrap of tape. –  KeithS Jul 16 '13 at 16:12
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