Have Backstabs Improved?

[kid_stevens]

I just refuse to backstab any device and honestly, i wish they would ban these types of connections, too many times have i pulled an outlet or switch only to have a wire pop out of the stab. I go so far as to tell my home owners that all of my terminations are done with twisted wires and wire nuts, and all devices are wired to the screw. It takes time and i think it is worth it./QUOTE]


Hear Ye Hear Ye

 

[klillemo]

Failure Modes for Screwed Connections and Sprung Connections

Failure Modes for Screwed Connections and Sprung Connections

I'm with Rob, there was no, "Never backstab" option. I really like Gunning's opinion on post #21.

Look at the surface area used on a backstab device, now compare that to a screwed terminal's surface area. The wiper on the backstab device is spring loaded. It is spring loaded by a metal that is susceptible to heat, a heat that can break the material down over time.

This is good summary of why I dislike backstabbing. My objection to backstabs is based on the nature of the failure mode. It is a cascade event due to the high susceptibility of the sprung metal connection to heat.

If the sprung metal connector is heated it becomes annealed and softens. This annealing action weakens the spring action and reduces the contact force. The reduced contact force increases the contact resistance and increases the power dissipated in the connection. The increased power dissipated in the connection raises the temperature of the sprung metal strip. Now it start all over annealing, weakening, dissipating and increasing the connection temperature until complete failure occurs.

Screw terminals are much less susceptible to a thermal failure due to not relying on a light weight spring connection with limited contact surface area. Screwed connections have significantly higher mass and contact surface increasing their thermal dissipation capability and reducing contact resistance.

Electrical connections heat up and it has nothing to do with the good work we do inside the wall. All it takes is device with a weak or damaged connection to be plugged into a receptacle. Even a moderate current can cause this connection in the PLUG to heat and the blades of the plug transfer the heat to our carefully wired receptacle. Because what is plugged into the receptacle, once we are gone, is out of our control even the best workmanship in backstabbing may not be enough to avoid a failure significantly earlier than would occur with a screwed connection.

I reject the conclusion that backstabbing and screw terminals are equally good based on the fact that some screw terminals fail as well. I accept that all connections will fail. The issue is which connection style is more robust AND is the weakest connection design robust enough.

With the higher susceptibility of the backstab connection to thermal runaway AND the demonstrated failures in the field, I find the argument against using backstabs compelling.

Whether to backstab or not is an individual judgment call as backstab connections are listed connections. This forum, at its best, is a way for us to discuss issues and make informed personal decisions with knowledge gained from our peers, and not just our own experience.

In my view, the understanding I gained from this forum has not been able to convince me that because the backstab connection is listed it is a connection that is good enough. My judgment tells me otherwise.

Cheers,

 

[hugh]

Backstabs

Backstabs

I have seen numerous occasions over the years where I go out on a service call and isolate the trouble to a backstab terminated receptacle. I am assuming this discussion pertains to some new design. I still would not trust this method of termination.

Many times I have experiences ranging from blackened or melted connections to wires that pull out if you remove the receptacle or switch. It does take more time but I firmly believe that the wire under the screw is a much superior and safer connection. Time saved by the installer is no excuse for what I consider to be an inferior method of attachment.

For the homeowner it can range from random needless services calls over an extended period of time (lifetime of house), to a potential fire situation in a house completed in this manner.

 

[Teaspoon]

I have ran into a lot of problems caused by back stab Switches & rec.
wires popped out. Have ran into mobile homes that were a night mare because of backstabbing. Do not back stabb my-self. Don't really care for the push-in connectors,
used in floursent lighting & some recessed lights.

 

[ohm]

This is good summary of why I dislike backstabbing. My objection to backstabs is based on the nature of the failure mode. It is a cascade event due to the high susceptibility of the sprung metal connection to heat.

If the sprung metal connector is heated it becomes annealed and softens. This annealing action weakens the spring action and reduces the contact force. The reduced contact force increases the contact resistance and increases the power dissipated in the connection. The increased power dissipated in the connection raises the temperature of the sprung metal strip. Now it start all over annealing, weakening, dissipating and increasing the connection temperature until complete failure occurs.

Screw terminals are much less susceptible to a thermal failure due to not relying on a light weight spring connection with limited contact surface area. Screwed connections have significantly higher mass and contact surface increasing their thermal dissipation capability and reducing contact resistance.

Electrical connections heat up and it has nothing to do with the good work we do inside the wall. All it takes is device with a weak or damaged connection to be plugged into a receptacle. Even a moderate current can cause this connection in the PLUG to heat and the blades of the plug transfer the heat to our carefully wired receptacle. Because what is plugged into the receptacle, once we are gone, is out of our control even the best workmanship in backstabbing may not be enough to avoid a failure significantly earlier than would occur with a screwed connection.

I reject the conclusion that backstabbing and screw terminals are equally good based on the fact that some screw terminals fail as well. I accept that all connections will fail. The issue is which connection style is more robust AND is the weakest connection design robust enough.

With the higher susceptibility of the backstab connection to thermal runaway AND the demonstrated failures in the field, I find the argument against using backstabs compelling.

Whether to backstab or not is an individual judgment call as backstab connections are listed connections. This forum, at its best, is a way for us to discuss issues and make informed personal decisions with knowledge gained from our peers, and not just our own experience.

In my view, the understanding I gained from this forum has not been able to convince me that because the backstab connection is listed it is a connection that is good enough. My judgment tells me otherwise.

Cheers,

A lot has been said on this subject but IMO kilillemo said it best.

 

[kid_stevens]

The worse push ins I know of are the tombstone ones. I love the ideal pushins for new wiring as long as the wires are not bent right at the connector. Wagos take up too much box space. But both hold a lot better than the back stab receptacles.

You can even cause a higher than normal failure by removing and then reinserting the connectors.

 

[Greg Swartz]

I too backstab...

I guess that I have seen problems on both sides of the coin: Loose screws and loose springs...

I've pulled outlets out and wires come loose in either case.

I can't argue either way, because both have failed.

Someone said it: It is UL listed, and NEC approved.

I'm a back stabber, I'm a back stabber (sung to the tune of: I'm a girl watcher)