Has anyone torn apart a receptacle and seen exactly how much contact surface area there is with the back-stab connection?
I don't want to open a can of worms but am curious if there's enough surface contact to prevent a hot spot from developing on the first receptacle when there's a load on the last in a series of receptacles.
Shhhhh! Back stabs are great, if they stopped using them, a large percent of our service calls would dry up. This week was a good example of the wonders of back-stabs, as soon as the tempeture snaps, the calls start comming in, yes the down stream load, will be on the first recpt.
I can't tell you how many of those have literally come undone in my hands when I go to pull a device out...granted they are an easy service call, but scary to know that is still a n approved connection.
I have taken apart two and have even made drawings of them. Unfortunately, they are in TurboCad format. Both are made of brass and are marvels of stamping engineering. One, probably the cheaper one, has a hole slightly smaller than the wire diameter punched in it. There are two parallel slots about 1/2" long running from the top and bottom of the hole. This creates a spring which holds the wire in place. The contact area is a bit less than the circumferance of the hole times the thickness of the brass.
The other is bent in such a way to form a right angle; imagine a piece of angle iron. The wire fits into the crotch of the angle and another bit of the brass is formed into a little spring that forces the wire into the crotch. I think this is a better contact and seems to be similar to the method used in "WAGO" connectors. ~Peter
Yes, in fact, I find that the quickest way to disconnect backstab connections is to simply crush the outlet or switch with a pair of vise-grips or channelocks and then pull the wires out of the metal clips. There isn't much contact area on those. It's also scary how easy it is to crush an outlet or switch..it's much quicker than futzing around with a screwdriver to release the backstab connections.
The infamous back-stab revealed! This is (was) a Leviton 15A 120V light-duty light switch.
Honestly, there's a surprising amount of contact area in there- there is a dimple sized for #14, and a large spring to hold it in place. The wire would have to be as straight as possible, though, or else it might only contact at 1 or 2 points instead of along the length. But installed properly, 3/8" of the wire will have contact along about 180° of circumference.
Edit: it's stamped MADE IN USA, btw
[This message has been edited by SteveFehr (edited 01-24-2007).]