by the way, are "spec grade" devices always referring to Fed Spec Number: WC596 ??
Using either table to get the area of the conductor and looking at the picture you posted of the receptacle with the stab-loc connection we can come to the conclusion that if the conductor is terminated using the proper method the area of contact with the receptacle is far more than the area of the conductor.
If the contact area of the conductor is more than the area of the conductor itself then the amount of current flow is not impeded in any way.
Then what causes the failures that everyone seems to be finding? It must be one of two different things. One the termination was done improperly or the device was overloaded. In either case it was not the fault of the method of termination but the misuse of the device.
What many find hard to believe is that even methods such as using an upturned lug or wrapping the conductor around the screw can fail if done improperly. How many devices have you found that the screw was not to the proper torque? This is common on the neutral terminals in panels. Ever see the white turning brown on these conductors?
Over the years of my experience I have learned that saying one method is inferior to another or that one electrician is inferior to another gets one nowhere but in the lime light of an ego trip. The truth of the matter is that the push-in method is just as reliable as any other method as long as the proper method is carried out when doing so and no matter how it is done the device is only rated for 12 amps. A case in point is using the device for a feed through connection. Personally this is not something I look at as being a good idea using either method of termination. I have always only connected three conductors to a receptacle, one black, one white, and one EGC. It is common practice to feed through the device but in the event of a repair then the entire circuit is opened but if only one conductor is terminated on the device one does not open the entire circuit doing a repair nor is the first device carrying the entire load of the circuit.
The one thing you will never hear come from my lips during a service call is that my method is any better than the person in front of me. What I do is spend that energy explaining to the homeowner that they need to get rid of that tender box they have plugged into the failed device. I take the time to explain that the device will only handle 1440 watts of continuous current flow and that continued current flow of more than this will cause the device to fail and end up costing them at the very least a service call but could end up costing them everything they own.
What is the continuous current rating for a 20A duplex receptacle?
The back wired way has that tensioned piece of metal that holds pressure against the wire. This keeps the wire in place and from falling back out of the receptacle but it doesn't keep the wire from turning in the terminal hole. If it can turn it is not secure. The proper way to make connections is to use the side setscrews or brackets under them to tightly grip the wire to these devices. This is the way the professionals would do it and that should be a clue to which connection is the appropriate connection.
A true professional will install anything according to the instructions included in the listing and labeling of the equipment as outlined in NEC Section 110.3(B). The instructions that is included in the listing and labeling of the devices in question in this thread say to strip the conductor to the strip gauge on the device and insert it into the hole in the back of the device.
Of course there are many DIYers that think they are far superior in knowledge than those who design the equipment they want to use and have found many different methods of making installations that exceed the standards by which the equipment is manufactured.
The bottom line is that one method when done properly is no better than another. Anyone who says different is doing nothing more than expressing their opinion as these devices are tested every day of the week for the method listed. If there was a safety issue with the method then UL would not list it as a method of terminating a conductor to the device.
Once they are mounted it the box they will not move.
But they may turn a bit while installing, but that should not be a problem.
Most of the install errors that I have seen, Is the nicking of the conductor when removing the insulation, and that is a No No.
Seeing is believing. Side wired you can see. Back wired you cannot. Stop drinking the kool-aid. Side wired is more secure.
This is my point only. Side wired is more secured. I can deviate back-wired connection with about 45 lbs of force. With the same forc the side wired connection is unscathed.
Test is proof positive.
Brother Don you have hit the nail on the head with most problems found in residential wiring or at least let me say that it has been my experience.
Young journeyman stripping conductors twist the strippers to and fro breaking the insulation free, opps the damage is done but they don’t trim it off and start over they just continue on without a care in this world.
Grab the conductor in the wrong hole of the strippers and then move to the correct hole, sorry damage is already done to the conductor.
One of my most favorite is the fellow grabbing two conductors at one time with dime store strippers that are not designed for the purpose.
Taking a phrase from some who are against the stab-loc, “if I had a nickel for every time,” I have found a handful of white conductors joined with a wire nut and one or two in the middle would be broke completely free “I would be a millionaire.” This comes from ringing the conductor with the strippers and also causes the burning of the stab-loc connection. We like to bend the end so when we do damage the conductor it breaks off and tells us we goofed.
When having lab with one of the classes I watch for this and try to head this habit off before it ever gets started by holding the stripped part of the conductor in my lineman’s pliers and with a couple of bends it breaks clean.
People do it and aren’t aware that they are damaging the conductor. No concentration at all, to busy jumping around to the beat of that awful mess coming out of that radio blasting louder than the jack hammer in the background.
Geez what is this world coming to? Next thing you know they will be demanding a water cooler and a chance to run to the port-a-jon every 30 minutes. That ain’t the half of it, they will be wanting to get paid to drink that water so they will have a reason to run back and forth on payroll.
As to deviating, I suppose that anyone could deviate from anything if they try hard enough. For the wire binding screw of a device one could deviate in many different ways such as but not limited to turning the conductor counter clock wise around the screw, stripping to much conductor, stripping not enough conductor, damaging the conductor during the stripping process, not tightening the screw enough, or even trying to secure the conductor to the screw by exerting 45 pounds of torque and stripping the threads of the screw.
So just what is you point again?
Not wanting to be rude but the only proof positive I can find in this post is that you are very unsure of your comments and know little about the amperage rating of the device you are installing. You seem to be saying that by using the wire binding screw somehow makes the device rated for more current or that the securing of the conductor by the screw where it takes 45 or more pounds to remove the conductor that somehow this makes the device better.
Get a spec sheet form Leviton and you will see that the required torque for tightening of the screws is 14 ft. lbs. and would you like to guess what the foot pounds of the stab-loc of the same Leviton receptacle is?
Seeing is not always believing. I can make a quarter disappear right before your eyes but it did not disappear it was sly of hand and you believe you saw the quarter disappear. Education is where believing comes from. Seeing all the complied data from the testing labs is where seeing is believing comes from not from looking at something.
A very simple question we can ask ourselves to ascertain the information concerning this topic is, if it were no good then why do they continue to manufacture the devices with stab-loc. The simple fact that the devices are continually being manufactured with stab-loc says something to those willing to learn.
But if your mentality is, I know more than those who design and test these devices then there will be no future education as you already believe you are smarter than those who made the device you are installing.
The device in question is rated for 12 amps. Using the wire binding screw and tightening the screw to just before stripping the threads and the device is still rated for 12 amps. Failure of the device starts anywhere above 12 amps no matter the method used to terminate the conductor.
We can install #12 cable and terminate using the screw but the device is still rated at 12 amps. Nothing we do will change the fact that the device is rated at 12 amps but there are many who believe that using #12 conductors and terminating using the screw someway makes it a better installation when the fact remains that the device is rated at 12 amps. These are the facts weather you believe them or not. Believe it or not but the receptacle is still rated for 12 amps.
As a side note, I suppose the 'area of contact' idea allows for side-wiring without looping the wire around the screw.