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I am replacing all my electicial outlets and only one has wires that are too big to put into the back of the new outlet. Any suggestions?

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What do you mean 'put into the back'? Are you using the push connectors? If so, don't. Use the screw connectors. If you mean the wires won't fit the box, then you'll need a bigger box. – DA01 Apr 30 '11 at 1:18
You didn't mention it, but 12 gauge is common with aluminum wiring (it's equivalent to 14 awg copper, for 15A circuits). If you have aluminium wiring, you need to use CO/ALR-rated fixtures or pigtail to copper with CO/ALR-rated wire nuts and use anti-oxidant paste. You can tell aluminum by the wire color looking silver when freshly stripped, blacker when it's been exposed to air and oxidized, and it's much softer and more flexible than copper. – gregmac May 1 '11 at 3:24
Posters are assuming you live in North America. Is this a valid assumption? – staticsan May 2 '11 at 1:05
Assuming the wire is copper (not AL) and the circuit is protected with the correct circuit breaker, the simplest solution is to get a short length of wire that does fit your new receptacle and connect it to the existing wiring with wire nuts. – Philip Ngai Apr 25 '12 at 21:50
Just because a wire fits in the backstab terminal doesn't mean you can safely stick it there. The quickwire terminals of some older receptacles accept 12 AWG wire, but Code has since changed to restrict quickwiring to use with 14 AWG wire only. – Jeremy W. Sherman Jul 13 '12 at 21:44

As long as you are going through the trouble to replace your receptacles, I have some recommendations:

  1. Choose high quality models, especially those labeled "commercial" or "industrial" grade. They have tougher plastics that won't break as easily. I've often seen cheap receps break and lose bits of plastic, and they are left in service for decades.

  2. Choose receps that have a contoured face. This makes it easier to get the plug in the right spot in the dark or behind furniture. Otherwise, it's tempting to use your finger to guide the plug in to the hole, which makes it easy to get shocked.

  3. Get receps that have screwdown clamps. These are easier to install than wrapping the wire around a screw; more secure than stabbing in the back of those crappy receps; easier to remove than both.

  4. Install tamper-resistant receptacles. These are code-required in many places, and they're a good idea.

As others have noted, it sounds like you're trying to insert 12ga wire in to a hole that only fits 14ga (for a 15A circuit). Don't use that feature; see #3.

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I have seen two types of screw down clamp outlets. Ones with a floating square "washer" on the outside, and ones with a floating square "nut" on the inside. I prefer the ones with the square nut on the inside. – Brad Gilbert Jun 25 '11 at 5:54
I have come full circle on my preference. I've used all the fancy ones; washers inside\outside, fold-out screw cover 'ears'... Now I'm back to making a loop around the screw (seriously, +10 seconds) and I sleep better knowing it won't be my fault your house burnt down. – Mazura Nov 28 '14 at 11:05

You probably have 12 gauge wire on that part of the circuit, which won't fit into the push-in connector on the back of a 15A receptacle (it's only good for 14 gauge). Is that the only receptacle on that branch circuit? If so, it might be a 20A circuit, so you'd need a 20A receptacle (otherwise you risk overloading the receptacle and damaging it, which could lead to a fire):

Picture of 20A receptacle

But as @DA01 says in his comment above, always use the screw terminals. They give a much more secure connection.

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Just as an FYI, according to my NEC-2002 code book, you can put 15A receptacles on a 20A circuit. – billoreid May 4 '11 at 12:51
Actually most 15 amp outlets I have taken apart ( to salvage the brass ) were identical to 20 amp outlets. – Brad Gilbert Jun 25 '11 at 5:48
You can put 15A receptacles on a 20A circuit. A 20A circuit is able to safely supply up to 20A of power draw. A 15A receptacle can safely supply up to 15A of power draw, which obviously can't exceed the 20A its circuit can supply. The T-shape prong on a 20A plug prevents plugging a device that draws more than 15A into a receptacle that can't safely deliver that kind of power. – Jeremy W. Sherman Jul 13 '12 at 21:32
@Craig At no point did I say to use 15A outlets instead of 20A outlets. That was a comment based on the one before it. ... I didn't have to measure the thickness because the shape of the metal piece has a T-shaped slot that the 20A outlet has. They did that so they only have to stock one part for both halves of 15A & 20A outlets. – Brad Gilbert Dec 1 '14 at 12:25

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