Modern electrical outlets - side wiring with 12 gauge

[Stephen Tashiro]

Do electricians "back wire" most modern electrical outlets when using 12 gauge wire?

Years ago, electrical outlets were designed to be "side wired" by hooking the wire around a screw. Some also had holes where a wire could be connected by pushing it into the hole, but this method of wiring by "back stabbing" was reglarded as unreliable. Nowadays I find electrical outlets are designed so they can be "back wired" by pushing the end of the wire between metal plate and a screw that holds the plate. As I understand it, this method is regarded as reliable.

I'd prefer to side-wire receptacles, but I find that it's very hard to fit 12 gauge wire around the screws of modern receptacles because the screws won't stay still due to their attachment to the plates needed for back wiring. The modern designs have the screw down in a recess where I can't fit a hooked wire without nearly taking the screw all the way off.

[Ron Selzer]

IF IT IS THE TYPE THAT THE SCREW TIGHTENS A CLAMP THEN it is the best way, better than side wired
Leviton 5252 or equivalent
Ron

[Jim Becker]

Backwired (with the clamping setup) is faster, easier and considered reliable, so that's why it's pretty popular. You can still side wire with the wrap if you prefer, but as you note, it's harder to do with the thicker 12 gage wire used in many circuits today. I always double check the clamping before I jockey the outlet into the box and 12 gage is fun there, too, because it doesn't bend as easily and that can put a good bit of pressure on the connection as you fold things together.

[Ken Combs]

Backwired (with the clamping setup) is faster, easier and considered reliable, so that's why it's pretty popular. You can still side wire with the wrap if you prefer, but as you note, it's harder to do with the thicker 12 gage wire used in many circuits today. I always double check the clamping before I jockey the outlet into the box and 12 gage is fun there, too, because it doesn't bend as easily and that can put a good bit of pressure on the connection as you fold things together.


Agree with all of that. Most duplex recepts now are rated 15A and 20A pass through. That is the reason that side wiring is hard for 12ga as most get 14ga. The installation gets easier if you pigtail all the wires and only bring two out to the recept. That way you can push the splices and bulky wire nuts to the back of the box and only bring the two pigtails out to the recept

[Julie Moriarty]

Do electricians "back wire" most modern electrical outlets when using 12 gauge wire?.

No. Back in 1974, when I was a first year apprentice, I almost used the "stabs" in the back of the receptacle when my journeyman had a bit of a fit. "Don't ever use those things! They are a fire hazard!" Over the years I passed that on to any apprentices working with me.

[Doug Dawson]

No. Back in 1974, when I was a first year apprentice, I almost used the "stabs" in the back of the receptacle when my journeyman had a bit of a fit. "Don't ever use those things! They are a fire hazard!" Over the years I passed that on to any apprentices working with me.
To be clear, there are 3 types of connections:
1) backstabbers, where the wire is inserted into a hole in the back of the receptacle, and is held in place by spring action; you can’t even physically use this for 12ga anymore; they are removed by snipping off the wire at the receptacle, because the wire is damaged and can’t be reused anyway.
2) side wiring, where the wire is inserted into a hole or semi-circular depression in the back corner of the receptacle and tightened down/clamped to a conductive plate using one of the side screws; this is okay.
3) loop wiring, where the wire is made u-shaped and looped around the screw clockwise and tightened down. This is also good, but is more prone to loosening than 2 if you’re not careful and lock/tighten the loop around the screw. In either case proper tightness must be observed (a torque wrench is useful, but most sparkies just do it by feel when the inspector isn’t looking. :^)

Julie is referring to mode 1 (one).

[Ron Selzer]

To be clear, there are 3 types of connections:
1) backstabbers, where the wire is inserted into a hole in the back of the receptacle, and is held in place by spring action; you can’t even physically use this for 12ga anymore; they are removed by snipping off the wire at the receptacle, because the wire is damaged and can’t be reused anyway.
2) side wiring, where the wire is inserted into a hole or semi-circular depression in the back corner of the receptacle and tightened down/clamped to a conductive plate using one of the side screws; this is okay.
3) loop wiring, where the wire is made u-shaped and looped around the screw clockwise and tightened down. This is also good, but is more prone to loosening than 2 if you’re not careful and lock/tighten the loop around the screw. In either case proper tightness must be observed (a torque wrench is useful, but most sparkies just do it by feel when the inspector isn’t looking. :^)

Julie is referring to mode 1 (one).

Agree with above
I was referring to mode 2 using a different description, however the Leviton 5252, along with I believe Pass & Seymour 5252 and Hubbell 5252 are the type of receptacle I use

Ron

[Tom M King]

I had a thread, not too long ago, where I purchased several different types, and compared them. I think in the Shop forum.

[Doug Dawson]

Agree with above
I was referring to mode 2 using a different description, however the Leviton 5252, along with I believe Pass & Seymour 5252 and Hubbell 5252 are the type of receptacle I use

You could call it side-wiring or back-wiring, but calling it back-wiring can be considered inflammatory. :^)

[Curt Harms]

No. Back in 1974, when I was a first year apprentice, I almost used the "stabs" in the back of the receptacle when my journeyman had a bit of a fit. "Don't ever use those things! They are a fire hazard!" Over the years I passed that on to any apprentices working with me.

There are pictures here and elsewhere to back up your journeyman. Those are the ones that didn't burn the house down.

[Frank Pratt]

No. Back in 1974, when I was a first year apprentice, I almost used the "stabs" in the back of the receptacle when my journeyman had a bit of a fit. "Don't ever use those things! They are a fire hazard!" Over the years I passed that on to any apprentices working with me.

I have a good example of what happens when the back stabber connections are used on my "wall of shame" Those things should never have been approved. The back connections that use the screws to tighten the wire are fine though.

To digress a little though, I have used Wago connectors that use a similar captive spring to make the connections & they are reliable. Much better engineering & manufacturing with those though.

[Julie Moriarty]

I have a good example of what happens when the back stabber connections are used on my "wall of shame" Those things should never have been approved. The back connections that use the screws to tighten the wire are fine though.

To digress a little though, I have used Wago connectors that use a similar captive spring to make the connections & they are reliable. Much better engineering & manufacturing with those though.

Scotchlok makes what we called "suitcase" connectors.
https://multimedia.3m.com/mws/media/1104021P/conector-scotchlok-idc-562.jpg
I first saw them on a job that had rows and rows of fluorescent fixtures, connected end-to-end, running down aisles. Pull the wire straight through the fixture housings, wire nut the last one and use those suitcase connectors for all the rest.

When I saw how they worked I asked the foreman why we are using them and pointed out the universally accepted "no back stabs" as proof these connectors are a bad idea. To make patters worse, the tiny wire coming from the ballast was too small for the blade to firmly capture it. The foreman pointed out the labor savings using the suitcase connector and advised me to fold over the ballast wire to make a better connection. I replied with something to the effect, "I thought quality and safety were more important than making a buck." I was on that job for months but eventually the connectors began to fail. They, too, made the "Do not use" list.

[Rob Damon]

For the most part you will see the back wiring push-in on residential work. All of the Commercial work we design we spec, requires side wiring.
If the receptacle is UL listed, it has been tested and complies with UL testing requirements regardless of the connection method.
The issue with residential wiring is most electrical contractor will use the smallest/shallowest single gang outlet box they can get to save money and when you leave 6" leads in the box, and you push the receptacle in the box, it will over bend the wire and that's usually what causes the stress issue.
On commercial work, we require the contractors will provide 4"x4" square boxes with single gang raised drywall plates which leave plenty of room for the device and the wiring.

[Frank Pratt]

Scotchlok makes what we called "suitcase" connectors.
I first saw them on a job that had rows and rows of fluorescent fixtures, connected end-to-end, running down aisles. Pull the wire straight through the fixture housings, wire nut the last one and use those suitcase connectors for all the rest.

When I saw how they worked I asked the foreman why we are using them and pointed out the universally accepted "no back stabs" as proof these connectors are a bad idea. To make patters worse, the tiny wire coming from the ballast was too small for the blade to firmly capture it. The foreman pointed out the labor savings using the suitcase connector and advised me to fold over the ballast wire to make a better connection. I replied with something to the effect, "I thought quality and safety were more important than making a buck." I was on that job for months but eventually the connectors began to fail. They, too, made the "Do not use" list.

I've never found an insulation displacing connector, even from 3M, that worked reliably for power applications.

[Charlie Velasquez]

Do electricians "back wire" most modern electrical outlets when using 12 gauge wire?

Years ago, electrical outlets were designed to be "side wired" by hooking the wire around a screw. Some also had holes where a wire could be connected by pushing it into the hole, but this method of wiring by "back stabbing" was reglarded as unreliable. Nowadays I find electrical outlets are designed so they can be "back wired" by pushing the end of the wire between metal plate and a screw that holds the plate. As I understand it, this method is regarded as reliable.

I'd prefer to side-wire receptacles, but I find that it's very hard to fit 12 gauge wire around the screws of modern receptacles because the screws won't stay still due to their attachment to the plates needed for back wiring. The modern designs have the screw down in a recess where I can't fit a hooked wire without nearly taking the screw all the way off.
Not sure of the brand outlet you are using, but in theory those side wired clamping connection were designed so when turning the screw clockwise to tighten you were not exerting force pushing the wire out.

Check, when you back the screw out as much as you can, rotate the outlet so the screw is on the bottom. The clamping bar should drop down. A #12 wire should slide in easily. That bar has a hump in it and the bottom plate has a corresponding hump. It will surround your conductor , increase surface contact, and apply even clamping pressure without applying force opposite the insertion angle. On the outlets I have used, if you try to put the conductor between the screw and the clamp, you lose 2x the height of that hump.

[Stephen Tashiro]

Not sure of the brand outlet you are using, but in theory those side wired clamping connection were designed so when turning the screw clockwise to tighten you were not exerting force pushing the wire out.


That's what I'm calling "back wiring" and I have no problem doing it. By "side wiring" I mean looping the wire around the screw - the way wiring was done years ago.

[Bill Dufour]

I am not sure if the wire loop thing is allowed with stranded wire or not. I have some #10 telephone wire and it is very flexible. Similar to an appliance cord, probably over 100 strands.
Bil lD

[Stephen Tashiro]

I am not sure if the wire loop thing is allowed with stranded wire or not.

I not sure either, but I've never needed to use stranded wire on electrical outlets.

[Weogo Reed]

Hi Folks,

In my opinion, scotchLoks and their ilk are only acceptable for
non-important, temporary, low power use.
That said, punch-down connections are used extensively for a wide variety of connections.
Good quality punch blocks used with the proper tool and proper wire in
an acceptable environment can hold up quite well.
To minimize long-term corrosion No-Oxid is helpful:
https://telephonetools.com/index.php?route=product/product&product_id=334bb
This can also be helpful on any connection that sees moisture.

Stranded wire can be used with standard electrical outlets - this is common in the event production world.
Do not wrap stranded wire around a screw.
The wire can be slipped under the clamping plate or a crimped spade or ring terminal can be used.

I'm not a licensed electrician - always follow local code!

Thanks and good health, Weogo

[Charlie Velasquez]

I not sure either, but I've never needed to use stranded wire on electrical outlets.

Have rolls of both #12 and #10 stranded. I almost always use 4" boxes, but if I know I will be closing in on my max box fill, I'll use stranded. A lot easier to fold into a box. A lot easier to pull if I have a number of turns, also.

For connections on the device using the side clamps, twist the strands tightly, insert and tighten.
To use loops around the screws, remove an extra 1/2"-3/4" more insulation than you think you need, twist the strands tightly in a counter clockwise direction, wrap around the screw and tighten. Both the DC twist and the extra twisted wire will help keep the conductor remain tight to the screw. Trim the excess with a pair of side-cutters.
To add pigtails use Wago lever nuts.

[Alex Zeller]

You do realize that wire nuts are used everywhere and are just a spring inside of a piece of plastic that pushes two (or more) wires together, right? That being said I don't use the "stab" style connections on an outlet. I have seen the wire pop out because the flat piece of metal that locks the wire in failed. As far as those "suitcase" style connectors go, if it's not slicing through both sides of the insulation and making good contact with the wire inside you have the wrong size. I have seen them used on factory wired 4' florescent light fixtures. I would trust them over the "stab" style connections but I would use a wire nut before using one.

[Malcolm McLeod]

...wire nuts are used everywhere...

Not everywhere. If I find a wire nut used on my projects on anything except a lighting circuit, I'll ask the foreman not to allow the offending electrician back on site. If I find a crimp-on butt splice in a conduit or wireway, the whole crew is escorted to the gate. Both are unacceptable risks in a production environment. We buy panels with oodles and gobs, even lots and lots, of screw terminal blocks for a reason.

Yes, I'm proof texting. Yes, I'm extrapolating from the context of the thread. And yes, I'm even being hyperbolic (...maybe just a wee bit;)). But, the subject is that important to me - - and for what its worth, given only 2 choices, I'd much rather have the 'iffy' spring cage clamp at a terminal or device, rather than a wire nut in mid-run.

Lagniappe: I learned to tug test 10% of the terminations in a panel; if I get a 10% failure rate on the tug (=1% of total), the electricians get to re-torque 100% of that panel. Once. Next time, another contractor gets to do it. (If you find an electrician that's really good inside a control panel, cherish them!)

...and now we return you to your regularly scheduled outlets.:)

[Jim Matthews]

I was taught to avoid back wiring where significant vibration is present (Clothes dryers, Washing machines) and to employ pigtails for greater clearance when side connecting serial outlets on the same leg.

[Thomas McCurnin]

Any copper or steel on the side of the outlet can, if the outlet is not positioned perfectly, make contact with the steel box and either send a shock to you or trip a breaker. That is why those side wired switches and outlets are not favored, and if used, are usually covered with tape along the outside. Wiring to the back is much safer.

If there is any exposed copper or steel on the side of the switch or outlet, I cover them with tape. That is standard practice.

[Doug Dawson]

Any copper or steel on the side of the outlet can, if the outlet is not positioned perfectly, make contact with the steel box and either send a shock to you or trip a breaker. That is why those side wired switches and outlets are not favored, and if used, are usually covered with tape along the outside. Wiring to the back is much safer.

If there is any exposed copper or steel on the side of the switch or outlet, I cover them with tape. That is standard practice.
You would have to be exceptionally sloppy to have the side wiring of a receptacle or switch come anywhere near close to shorting out against a metal box. Neatness rules the day. However, wrapping the device terminals w/electrical tape is always a good idea, for the reason that those pesky kids are good at prying off cover plates and sticking stuff in there (as well as people carelessly trying to pull out a receptacle without first verifying if it’s live or not.)

Crazy stuff can happen in a box under pressure, and I have personally seen Wago 221 connectors come loose in the fracas melee, so it’s good to wrap those too if you anticipate such.

[Doug Dawson]

I not sure either, but I've never needed to use stranded wire on electrical outlets.
Wire inside a wall or junction box doesn’t have to be flexible, so there’s no need for it to be stranded, and I’ve never seen anything like that.

[Doug Dawson]

Not everywhere. If I find a wire nut used on my projects on anything except a lighting circuit, I'll ask the foreman not to allow the offending electrician back on site.
What kind of projects are those?


I learned to tug test 10% of the terminations in a panel; if I get a 10% failure rate on the tug (=1% of total), the electricians get to re-torque 100% of that panel.
You should be tug-testing _all_ of them. :^)

[Jason Roehl]

Wire inside a wall or junction box doesn’t have to be flexible, so there’s no need for it to be stranded, and I’ve never seen anything like that.

A lot of commercial/industrial wiring is done in conduit, with stranded wire. It’s easier to pull through the conduit. Wire companies now make some insulation that is super slick to make pulling it through conduit that much easier. At work, my building is all conduit, and if I install a new receptacle or replace one, I pigtail the stranded wire in the box with some short pieces of solid to make the connection with the receptacle, under the clamp or around the screw.

[Doug Dawson]

A lot of commercial/industrial wiring is done in conduit, with stranded wire. It’s easier to pull through the conduit. Wire companies now make some insulation that is super slick to make pulling it through conduit that much easier. At work, my building is all conduit, and if I install a new receptacle or replace one, I pigtail the stranded wire in the box with some short pieces of solid to make the connection with the receptacle, under the clamp or around the screw.
My solution to that is GB Wire-Aide wire-pulling lubricant.

[Jim Matthews]

... if I install a new receptacle or replace one, I pigtail the stranded wire in the box with some short pieces of solid to make the connection with the receptacle, under the clamp or around the screw.

That's how I was taught, too.

We carried a box full of "preloaded" standard receptacles.
The only wiring we did on site was GFI.

[Malcolm McLeod]

What kind of projects are those?

You should be tug-testing _all_ of them. :^)

Primarily pumping systems; the electrician tests 100%, I am just doing random QC re-check.

[Roger Feeley]

I used stab outlets in my old shop to wire lights. When I ripped out that wiring to sell the house, a bunch of those wires were loose. I vowed never to use them again. Those were 20 years old.

I just discovered that the electrician that wired my house used stab receptacles. Have stab receptacles gotten better? Should I go through the house and replace them?

[Jim Matthews]

RE: stab outlets Should I go through the house and replace them?
I would only do so with outlets that exhibit intermittent failures.

If the circuit breaker holds (doesn't often trip and can be reset) I would leave well enough alone.

(I'm a hack, but I handle simple repairs at home.)

[Jim Becker]

Any copper or steel on the side of the outlet can, if the outlet is not positioned perfectly, make contact with the steel box and either send a shock to you or trip a breaker. That is why those side wired switches and outlets are not favored, and if used, are usually covered with tape along the outside. Wiring to the back is much safer.

If there is any exposed copper or steel on the side of the switch or outlet, I cover them with tape. That is standard practice.

For the modern outlets, etc., that have the side clamping mechanism, there's no more chance of contact with the side of the box than with traditional "around the screw" setup. In fact, there is slightly less because the screws will project less when they are used to secure the wire clamping mechanism than when there's a piece of wire around them.

That said, it's my own personal standard practice to do a wrap of tape around them no matter how they are wired...

[Frank Pratt]

I just discovered that the electrician that wired my house used stab receptacles. Have stab receptacles gotten better? Should I go through the house and replace them?

If it was my house, I'd fix them all. You probably don't have to replace the receptacles because they usually have side wired terminals as well. I've seen those back stab connections completely destroy a receptacle.

[Frank Pratt]

Any copper or steel on the side of the outlet can, if the outlet is not positioned perfectly, make contact with the steel box and either send a shock to you or trip a breaker. That is why those side wired switches and outlets are not favored, and if used, are usually covered with tape along the outside. Wiring to the back is much safer.

If there is any exposed copper or steel on the side of the switch or outlet, I cover them with tape. That is standard practice.

Taping the outlets is not a bad thing, except for the added labor. Unless the box has been bent in, the side wired terminals will not touch the box. Even marginally neat work habits will keep that from happening. If somehow the terminals do touch the box, there is no shock hazard. The breaker will just trip.

To say that taping devices is usual, or standard practice is a huge stretch.

[Frank Pratt]

A lot of commercial/industrial wiring is done in conduit, with stranded wire. It’s easier to pull through the conduit. Wire companies now make some insulation that is super slick to make pulling it through conduit that much easier. At work, my building is all conduit, and if I install a new receptacle or replace one, I pigtail the stranded wire in the box with some short pieces of solid to make the connection with the receptacle, under the clamp or around the screw.

Ever used the Pass & Seymore Plugtail system? The receptacles come with a pigtail harness consisting of stranded wire leads that terminate in a plug that connects to the receptacle. the tails are connected to the wires after pulling them in & then at finishing stage, the receptacles are plugged into the tails.

The advantages being easy device replacement without shutting the power off and a circuit can be energized without having all the receptacles installed. Pricey though, but they are spec grade.

[Weogo Reed]

Hi Malcolm M,

I agree that all splices can only be in accessible boxes, not in conduit/wireways.

I'm not an electrician but have been using wire nuts for more than forty years.
Please school me in why they are only acceptable for lighting circuits.

Thanks and good health, Weogo

[Frank Pratt]

Hi Malcolm M,

I agree that all splices can only be in accessible boxes, not in conduit/wireways.

I'm not an electrician but have been using wire nuts for more than forty years.
Please school me in why they are only acceptable for lighting circuits.

Thanks and good health, Weogo

Wire nuts are perfectly acceptable and reliable for power connections. There are some critical installations where engineers may specify crimp or other type connection. I am an electrician & have been using wire nuts for over 45 years.

[Stephen Tashiro]

I just discovered that the electrician that wired my house used stab receptacles.

In what year was the house wired?

[Malcolm McLeod]

Hi Malcolm M,

I agree that all splices can only be in accessible boxes, not in conduit/wireways.

I'm not an electrician but have been using wire nuts for more than forty years.
Please school me in why they are only acceptable for lighting circuits.

Thanks and good health, Weogo

I deal with industrial automation & control systems. If a faulty connection causes a life safety related transmitter to re-boot, it could E-Stop the entire facility, and it can cost millions to get it back online. Same potential with a pump, for example - connection comes loose, pump doesn't start, tank level goes HIHI, facility E-Stop.

I diverge from this thread's context, but we deal with 4160V/3P medium voltage or 480V/3P low voltage for power, and 24VDC instrumentation primarily. Power gets crimp-on bolt lugs (or split-bolts for the small stuff(<15hp)). Instruments and actuators get crimp on ferrules - then everything gets secured w/ 'thread' - either a nut/bolt or terminal block screw.

There are only 2 duplex receptacles on most of 'my' sites, both in a pre-fab containerized MCC building, powered from a lighting panel bucket in the MCC: 1 for the network switch gear; 1 convenience outlet for a programmer. Direct wired; no wire nuts - tho' again, I was proof texting above, and for this specific 120V application I wouldn't put the run on someone. (I would question why they need wire nut on a 15ft wire run!?!)

...we now return control of your SMC monitor to you. We hope you've enjoyed this brief excursion to ... the Industrial Zone. ;)

[Frank Pratt]

In what year was the house wired?

Lowball electrical contractors have been using back stabs from when the came out (40 - 50 years ago?) to this day. I emphasize lowball, with all its negative connotations.

[Jason Roehl]

Ever used the Pass & Seymore Plugtail system? The receptacles come with a pigtail harness consisting of stranded wire leads that terminate in a plug that connects to the receptacle. the tails are connected to the wires after pulling them in & then at finishing stage, the receptacles are plugged into the tails.

The advantages being easy device replacement without shutting the power off and a circuit can be energized without having all the receptacles installed. Pricey though, but they are spec grade.

Interesting. I’ll certainly check it out, though I doubt it would be worthwhile for us—we don’t replace that many receptacles. I doubt I’ll be there long enough to replace a given recep more than once (even at about 20-25 years to go...).

[Bill Dufour]

I saw those for sale on ebay. Almost bought several until I realized you can not use them without the pigtail. the pigtail costs 5-6$ each. Buy a ten dollar outlet instead and it will outlast the pigtail life cycle.
What I mean is in 20-30 years you will not be able to buy a pigtail that fits. Same idea as a replacement rechargaeable battery tool in 30 years. I no longer have a VHS player but I do have few tapes.
Bil lD

[Wade Lippman]

To be clear, there are 3 types of connections:
1) backstabbers, where the wire is inserted into a hole in the back of the receptacle, and is held in place by spring action; you can’t even physically use this for 12ga anymore; they are removed by snipping off the wire at the receptacle, because the wire is damaged and can’t be reused anyway.
2) side wiring, where the wire is inserted into a hole or semi-circular depression in the back corner of the receptacle and tightened down/clamped to a conductive plate using one of the side screws; this is okay.
3) loop wiring, where the wire is made u-shaped and looped around the screw clockwise and tightened down. This is also good, but is more prone to loosening than 2 if you’re not careful and lock/tighten the loop around the screw. In either case proper tightness must be observed (a torque wrench is useful, but most sparkies just do it by feel when the inspector isn’t looking. :^)

Julie is referring to mode 1 (one).
While I have had several "1"s fail, I have never had a "3" fail, and have never used a torque wrench. I just can't see why "3" would would be more likely to fail than "2".

[Frank Pratt]

While I have had several "1"s fail, I have never had a "3" fail, and have never used a torque wrench. I just can't see why "3" would would be more likely to fail than "2".

Because you have 2 wires instead of 1 trying to torque the screw loose when the receptacle is pushed back in the box. Especially with #12 wire. I've personally seen it happen when installing one way back in the day.

[Stephen Tashiro]

Because you have 2 wires instead of 1 trying to torque the screw loose when the receptacle is pushed back in the box.

I don't understand why 2 wires would be involved in loop wiring a screw in a receptacle. Doesn't (proper) loop wiring only involve looping a single wire around a screw? (And using pigtailng to avoid having more than one wire per screw).

[Doug Dawson]

I don't understand why 2 wires would be involved in loop wiring a screw in a receptacle. Doesn't (proper) loop wiring only involve looping a single wire around a screw? (And using pigtailng to avoid having more than one wire per screw).
Another way to look at it is to consider that the highest stress the wire is under is when it's being pushed back into the box. In the case of side-wiring, that pressure is exerted to at least hold the wire in place, whereas with loop wiring, it is to push it away from the screw.

It's worth noting here that even experienced electricians have difficulty free-handing the tightening of the screws to within 10 percent of spec. Here's an interesting discussion of that: https://www.youtube.com/watch?v=H21lZxyvMNw

[Frank Pratt]

I don't understand why 2 wires would be involved in loop wiring a screw in a receptacle. Doesn't (proper) loop wiring only involve looping a single wire around a screw? (And using pigtailng to avoid having more than one wire per screw).

I may have interpreted #3 incorrectly, but I took it as referring to a situation where more than one receptacle i in a box. In that case, one could strip off a bit of insulation mid-wire, bend it into a U, and put it under the screw. The remaining tail then goes on to feed the next receptacle.

[Brian Elfert]

Ever used the Pass & Seymore Plugtail system? The receptacles come with a pigtail harness consisting of stranded wire leads that terminate in a plug that connects to the receptacle. the tails are connected to the wires after pulling them in & then at finishing stage, the receptacles are plugged into the tails.

The advantages being easy device replacement without shutting the power off and a circuit can be energized without having all the receptacles installed. Pricey though, but they are spec grade.

Are these for residential or commercial? How often does someone replace receptacles in a house to need a pigtail to make it easier?

[Frank Pratt]

Are these for residential or commercial? How often does someone replace receptacles in a house to need a pigtail to make it easier?

Could be either, but the are a higher end product & expensive.

[Brian Elfert]

Could be either, but the are a higher end product & expensive.

I could see maybe using in commercial environment if receptacles are going bad regularly due to heavy use. I don't see why it would be worth it for residential as receptacles shouldn't need replacement for several decades at earliest. My parent's house was built in 1979 and the receptacles are all original. My house was built in 1980 and many of the receptacles had no tension anymore. (Most of the stuff in the house was cheap and had to be replaced.) I replaced every switch and receptacle in the house. I bought a better grade of receptacles since the total additional cost for the whole house was maybe $30.

[Wade Lippman]

Because you have 2 wires instead of 1 trying to torque the screw loose when the receptacle is pushed back in the box. Especially with #12 wire. I've personally seen it happen when installing one way back in the day.

I understand your point. I always squeeze the loop together; I just can't see it doing much of anything.

[Doug Dawson]

I understand your point. I always squeeze the loop together; I just can't see it doing much of anything.
Squeezing the wire around the screw is the way to go, no doubt, if that’s what the receptacle requires. But the length of wire, however short protruding from the box, might dictate that you’re better off side-wiring (under the clamp,) and your life is made easier by using receptacles that support that.