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Thread: Question about Outlets and terminals/push-in(real question, not a troll)

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    DIY Junior Member cswilson's Avatar
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    Default Question about Outlets and terminals/push-in(real question, not a troll)

    Is it allowable to use BOTH screw and push-in's on the same receptical?

    My situation is this, I have 3x 14/2 romex running into a 12.5ci (2"x3"x2.5") box.
    the Ontario electrical code allows 6 conductors and 0 or 1 marret in that size of box.

    If I can use both screw terminals and 1 push in I would need no marrets, but if I can't I will have to try and find a 2x3x3 box.


    I personally use marrets and pigtails normally when connecting outlets, but because this box is a little small it has raised this issue

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    There are receptacles that have rear contacts that rely on a screw to clamp it in place. Those are fine for your application. I've never liked the ones that relied on spring pressure to hold it in place. Otherwise, maybe a bigger box is the safer way to go.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Electrical Contractor/Instructor jwelectric's Avatar
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    UL has tested the push-in connections on the back of receptacles and switches at their rated load and has approved them for this use.

    Should anyone come along and try to sell you the idea that the push-in connections are bad then they are trying to say that they are smarter than UL.

    What your propose is just fine and legal

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    Plumber jimbo's Avatar
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    jw..........what you say is of course completely accurate. But in the same vein, there are plumbers who use plumbqwik one piece stop/riser combos, and push on valve/riser combos....because they are UPC/IAPMO listed, and they speed up new construction. Some of the plumbers on the forum would never use such products, because experience tells us that these products do not have the same long term reliability as better ( slower install types) products do. It is just a personal choice. Which product to use can also of course be a stricly business decision.

    I am sure you have read or even posted on question from consumers trying to find why some of their outlets and switches do not work...and the answer often is a faulty push in connection. So you are correct....but those who might recommend sturdier products are also correct.....n'est pas? as Frenchy the electrician would say!

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    Electrical Contractor/Instructor jwelectric's Avatar
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    You are correct Jim in so much as ignorance builds a fear that can’t be explained away.

    From 1979 through 1987 about 98 percent of the work I did was apartment townhouses and condominiums. For this nine year period I carried the maintenance contract on all but two of these projects. The smallest project was 125 units with most being between 225 and 250 units. Each unit would have between 40 to 50 devices (switches and receptacles) that were installed using the stab-loc connection included with the device.

    Over this nine year period of installations I would estimate somewhere around 10 thousand units were wired with somewhere around three to four hundred thousand devices wired.
    Now I must ask if this stab-loc was so bad why I didn’t experience a massive failure back when the twenty amp circuits were included in the stab-loc.

    On the few failures (less than 50)and we almost always found portable electric heating equipment in use on the failed device. In the years of carrying the maintenance contract on these units not one switch failed. I am of the opinion that when there is a .0001 percent failure rate that the failure rate is nonexistent.

    What I have come to the conclusion of concerning the stab-loc connection is that all failures are the direct result of either misuse (overload) or improper installation.

    When these devices are properly installed and the circuit is not overloaded these type installations are just as safe and efficient as one wrapped around the screw. It has also been my experience that when the screw was used and the device overloaded the device would get to where the cord would not stay in the receptacle which is a blade being stabbed into the tension of the receptacle. Is this not the same principle as the stab-loc? So to say that the holes in the back of receptacles are bad, would not the holes in the front of the receptacle not be just as bad?????????

    As to the plumbing I have no answer as I do no plumbing or do I do research as deeply as I have the stab-loc devices.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by jwelectric View Post
    trying to say that they are smarter than UL.
    Hardly any organization ever admits they screwed up. You should have seen the gyrations the Patent Office went through when they failed to find a previous valid patent and so granted a new patent for the same invention.

    The customer is the ultimate testing lab and only statistically significant [hypothesis testing, double-blind studies, etc.] results count.
    Last edited by Thatguy; 11-06-2010 at 09:19 AM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The plug on a cord has MUCH more surface area, and spot heating and resistance is less on heavy loads. The prongs on a back-stabbed device have much less surface area (but higher pressure). Given a choice, I'd prefer a device with a larger contact area, and that means a screw or a screw and clamp. Especially in a feed-through situation, I prefer a better connection than those small spring prongs.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    I had a friend call yesterday, who has three outlets in the master bedroom which do not work while the other three do. After talking to him, it appears that the only source of the problem must be where those three attach to the other three. AND, since the wiring is done with "back stabbing", the inference is that one of them must be faulty. I also told him to plug a lamp into the bad outlets, because the simple process of removing the receptacle from the wall, COULD move the bad connection sufficiently to reenergize it. If that were to occur and he did not have a lamp which would illuminate when it happened, he would still not know where the problem was when he went back and retested the outlets and they were then working.

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    Engineer Furd's Avatar
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    JW posted:
    The area of contact of a stab-loc device is the area that is required for the 15 amp device to safely carry 12 amps which is the most that is allowed to be carried by any device installed on a 15 amp circuit installed in any manner in which it can be installed.
    Should more amperage be allowed on this circuit there will be a failure somewhere on the device carrying the current which is a DIRECT VIOLATION OF BOTH THE NEC AND THE LISTING OF THE PRODUCT.
    Please cite the source of these statements, especially "...12 amps which is the most that is allowed to be carried by any device installed on a 15 amp circuit..." It seems to me that you are confusing the requirement that continuous loads may only be a maximum of 80% of the circuit rating with the non-continuous rating of a device. To my knowledge there is NO limiting factor of 80% that must be applied to all devices in any and all service conditions.

    Or to put it another way, any device rated at 15 amperes should be able to carry that 15 amperes for a period of up to, but not more than, three hours of continuous operation without failure.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Furd View Post
    JW posted:
    Please cite the source of these statements, especially "...12 amps which is the most that is allowed to be carried by any device installed on a 15 amp circuit..." It seems to me that you are confusing the requirement that continuous loads may only be a maximum of 80% of the circuit rating with the non-continuous rating of a device. To my knowledge there is NO limiting factor of 80% that must be applied to all devices in any and all service conditions.

    Or to put it another way, any device rated at 15 amperes should be able to carry that 15 amperes for a period of up to, but not more than, three hours of continuous operation without failure.
    210.21(B)(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).

    Table 210.21(B)(2) Maximum Cord-and-Plug-Connected Load to Receptacle

    Circuit Rating (Amperes) Receptacle Rating (Amperes) Maximum Load (Amperes)
    15 or 20 15 12
    20 20 16
    30 30 24


    No it seems like I might know what I am talking about here.
    This is the Standard that UL has set forth for the manufacturing of these devices and the load at which they are to be tested.

    When a 1500 watt portable electric heater is plugged into one of these 15 amp devices they heat and the device is destroyed. 1500 divided by 120 volts equals 12.5 amps. Let this device be in series with other devices that are carrying a load of their own and now we have more than one device that is being affected.

    Now couple this with the trip curve of a breaker and we see that it is possible to load that receptacle to enormous amounts of heat and failure will occur. A general rule for the trip curve of a breaker is it will carry six times its rated current for two full seconds. It will carry three times it’s rated current for up to five minutes.

    As for all this area bull hockey that has been spread around in a futile attempt to prove that back-stabbing is some awful miscarriage of the electrical trade take a look at the end of a #14 conductor and tell me what the area of that conductor that under certain circumstances can carry 20 amps continually and explain to me again about all this contact area. Are you trying to say that the contact area for a conductor must be larger than the conductor in order for the conductor to carry current? Come on now let’s get real in this discussion.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    This is a little better. It is from the NEC

    Here is a picture showing the area of contact and as anyone can see the area of contact is the same as when under the screw as though this would really matter as the only area of contact is the wire itself




    Notice how the area is about the same as when under the screw unless you are so blind you can only see one side of the contact.

    Also notice that the blade of the plug is a pressure contact. When overloaded this contact point also gets weak and the plug gets to falling out, another type of failure due to overload
    Last edited by jwelectric; 11-08-2010 at 05:03 AM. Reason: added picture

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I'd still rather have the wire underneath a properly torqued screw or double-sided clamp. The area of contact assumes that the wire is straight (the rest of the structure requires it to be fairly straight) and the spring pressure. If the wire was slightly curved, it would still fit in, but may only make contact on a small area. Yes, this is a workmanship issue, but it is still an issue (to me!). Especially when the receptacle is being used as a junction, with the screw connections and the stab being used, I'd rather not rely on the back-stabbed connection. I've had more than one in my home that became intermittent and replaced it, and no, I don't use portable heaters or other heavy load devices on them. Do I believe that they work, yes. ARe they the better solution, no IMHO. I prefer a bigger margin of error.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    General Engineering Contractor ballvalve's Avatar
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    The average homeowner doesnt know an amp from a watt and even where his panel is located. Dont test the water with friction terminals.

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    General Engineering Contractor ballvalve's Avatar
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    To the guy that says heat will loosen the screw clamp connections, I would ask hiim to have a look at his main panel before making such comments. All those wires must be wiggling around!

    When we see PUSH IN connections on breakers and neutral bars, I'll be the first to use them.

    comparing a STAB, clamp, double sided connection to a bus bar or a meter terminal to chinese push in outlets is absurd.

    The ONLY advantage one might mention is if the electrician is mildly forgetful and neglects to turn the clamp screw at all. If you are a dopey electrician, by all means STAB dont SCREW!

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by ballvalve View Post
    heat will loosen the screw clamp connections
    Temperature changes will probably loosen machine screws unless precautions are taken, like using a close fit.
    http://www.sizes.com/tools/thread_screw.htm
    Last edited by Thatguy; 11-14-2010 at 02:07 PM.

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