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Backstabbing Receptacles

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petersonra

petersonra

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engineer
mbrooke said:
I disagree, I think the NFPA has slowly started to "wake up" realizing just how important an EGC is, and its integrity.

The surface area in a back stab is not the same as in a screw terminal, let alone that the wire can actually move around slightly as the metal expands and contracts breaking the cold weld.
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The back stab has a spring on it so thermal expansion just is not an issue.
 
kwired

kwired

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petersonra said:
The back stab has a spring on it so thermal expansion just is not an issue.
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yes but the spring on these devices isn't necessarily that great of a spring.

Some people say that "WAGO's" or similar connectors are the same thing, I don't think their spring is the same and possibly is more contact surface as well.
 
mbrooke

mbrooke

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kwired said:
Sorry don't think I do. Seemed to be common to find them if still original installed device on old NM cable with reduced size EGC.

Second EGC screw generally was on opposite side of the yoke from the first one.
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Interesting. Thanks :)
 
mbrooke

mbrooke

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petersonra said:
The whole arm is a spring that keeps pressure on the wire.
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Which-

1) expands and contracts

2) is sharp digging into the copper causing loss of tension

3) Most receptacle mounting screws are backed out so the outlet sits flush on the plate. Every time someone plugs of unplugs, the receptacle wiggles and so do to the conductors which in turn results the copper further digging into the "spring" while the cold weld is broken and re-made with top portion of contact.


It takes a very slight increase in R1+R2+R3+R4 contact matrix to cause a run away effect of joule heating.
 
kwired

kwired

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petersonra said:
The whole arm is a spring that keeps pressure on the wire. Note use of word "spring" in picture.
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Might not be very good spring but yes that is the concept.

Note it is same spring material as what gives you pressure to hold the inserted plug in place. If the plugs are starting to fit poorly the backstab probably not doing so great either.
 
mbrooke

mbrooke

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kwired said:
Might not be very good spring but yes that is the concept.

Note it is same spring material as what gives you pressure to hold the inserted plug in place. If the plugs are starting to fit poorly the backstab probably not doing so great either.
Click to expand...


Names are arbitrary to the electrical manufacturers and their organizations. 😉 Much like joule heating being "arcing"
 
petersonra

petersonra

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Northern illinois
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engineer
if you don't like backstabbing, you are free not to do so.

personally, i get a kick out of electricians who use the screws then wrap tape around the whole outlet assembly to prevent the loose ground wire from getting at the screws.
 
mbrooke

mbrooke

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petersonra said:
if you don't like backstabbing, you are free not to do so.

personally, i get a kick out of electricians who use the screws then wrap tape around the whole outlet assembly to prevent the loose ground wire from getting at the screws.
Click to expand...


That is actually a spec requirement in some institutions.
 
petersonra

petersonra

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Location
Northern illinois
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engineer
mbrooke said:
Isn't that also if the cover falls off in say a nursing home the occupant won't be shocked?
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I have never seen it done except where Romex is used. It seems likely to me it is because the installer is too lazy to coil the wires in an orderly manner and put them inside the outlet box instead of just jamming them in. With Romex there is a tail of bare wire that can go just about anywhere when care is not taken when the outlet is shoved into the box.
 
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