In my experience and spanning all degrees of quality and price, standard duplex receptacles, switches, etc. have wire retaining screws (the ones you fasten the hot, neutral, and ground wires to) which do not back out easily all the way. I assume this is to keep them from doing so inadvertantly. It appears that the threads of the screw are distorted at the end to accomplish that means. With a little concerted effort one can, without difficulty, completely remove the screws from the “appliance.”
A electrician friend of mine states that backing the screws out all the way to remove them (for example for attaching ring terminals, better access, whatever)then in turn, the screw distorts the female threads of the receptacle, switch, etc. When the screw is re-installed the tolerances of the threading is less than original. This sloppiness can lead the the screw connection working loose over time; electrical shorts, sparks, fire, global meltdown and so on.
I says he’s anal.
Replies
And I say, for the 43 cent cost of pitching that one, and using a new one, why worry?
If you are going to attach a ring terminal you'll have to back the screw out.
My experience is there is always a bit of play between the male and the female so I don't see a problem reinserting the screw.
Just wondering how they make that thread mismatch after putting the screw in.
Those screws have their threads distorted once they are inserted through the plate on the device. The manufacturers do this to prevent the screws from falling out while being shipped, these units are typically shipped with the screws backed out to save the electrician time, and to provide a warning that you are getting near to having the screw drop out.
Backing them out all the way makes reinserting them more difficult. It galls both threads pretty badly. I haven't seen any alerts or warnings about reinstalling the screws if you force them out. It logically would weaken the connection but how much is unknown and difficult, without some testing, to guess how dangerous it might be or become in time.
My question is why would you want to do this? Sure ring terminals are nice but pretty much overkill in anything less than a life safety mechanism like a vital medical circuit or maybe a fire pump. Even then I have seldom, perhaps never, seen it done. I have worked on a few HO wired jobs where they used crimp on terminals but this was largely amateurish attempt at security in light of inadequate knowledge and experience.
Terminals, IMHO,make some sense with stranded wire as stranded wire is formed hook is a proven method. In this case it would be faster and just as well to use a hook terminal. Better than a spade and almost as good as a ring.
You can use a 10-32 die to re-shape the threads on the screw before you re-insert it.
Perhaps the screws are made of brass, which is soft, but maybe the female hole is too. I doubt if the crimping on the screw is very severe and it probably gets mostly "uncrimped" when withdrawn. That is, the deformation would be just enough to prevent it from falling out during shipment.
There are some cases -- such as installing #10 solid copper -- in which the only way to get the loop on is to remove the screw.
~Peter
Another thought... how close to the threshold of stripped? I've found a couple in a rental I used to own, so I trashed them to be safe. stripped=loose connection, which =hi resis, which =heat, which =fire, right? So that last turn of the screw could be critical. Picture this, when you stuff it all back in the box, that motion could jar the lead connection enough to break the threshhold and maybe now its loose, and you don't even know it!
just a thought.
why not simply use spec grade switches & recepticals? Cost a bit more, but quality is there too.
Many of these screws,depends on brand and model, are plated steel. I have seen a few of these screws removed, by accident or purpose, that would not thread back in and have seen at least one that would not tighten. It would get tight, but not tight enough, and slip, typical for a stripped female thread. I suspect that a loose screw, and thus a loose connection, would be far more hazardous than any danger a hook terminal, as opposed to a ring, would pose.
The trick with #10 is to either pigtail on a length, about 3" is fine, of #12 solid or delicately corkscrew the hook when you form it. The first technique works and is legal because we are talking about 15A or 20A receptacles. The only reasons to run #10 to them is a voltage drop or derate situation. Neither would cause problems with #12 pigtail on a 20A circuit. A 30A receptacle would have a terminal more adapted to #10. The second method takes a touch and is not difficult once you get the hang of it.
The other point is that while you may or may not get away with removing the staked screw from a common receptacle do not remove the screw if the screw goes into a movable plate within the device. Doing so makes for a very time consuming situation that likely destroys the electrical integrity of the device because there is no way to keep the plate square as you reinsert the screw so cross threading is a certainty.
These movable plates are used to clamp solid wire, no stranded need apply, that is inserted straight into the back of the device. These are common to GFIs and some higher end devices but are not to be confused with the push-in connections that do not use a screw.
The only reasons to run #10 to them is a voltage drop or derate situation. The reason the #10 [white] wire was used was that the plans specified it for harmonic considerations. #12 was fine for the hot wire but this was a three phase circuit hence the super neutral. I did have my doubts about how nore amps could come out of the receptacle than went in so I posted this problem on another forum and was advised to follow the specifications. Perhaps you could provide more details on this "corkscrew" procedure.
Incidently, it is possible to [special] order MC cable with #12 black, #10 white and #12 green! I think the code was "12-1/w/ground/w/super neutral".
~Peter
I had assumed, not entirely without cause seeing as that this is a Homebuilding forum and most utilities are loath to install three phase to residences, that the wiring was single phase.
Even given that I find the use of "super neutrals, to be poor practice in the majority of the situations. Most harmonic problems have a lot more to do with poor design, sharing neutrals on switching power supplies or putting loads on a common circuit that are better put on a separate circuits. IMHO oversizing neutrals is not a substitute for good design even though some designers claim otherwise and use it as a value, cost, added item.
Given all this the #12 pigtail will still work just fine. This would be my preference. Pigtail onto the #10 run, this leaves the #10 electrically intact for feedthrough current and three phase purposes, and make up the circuit normally. The super sized neutral only counters the effects the additive harmonics common to a three phase circuits misused not to the single phase feeding a 15/20A device.
If you insist on using a #10 pigtail the "corkscrew" I refer to is simply a forming of the hook that goes around the screw in the manner of a corkscrew. That is the hook does not lie in one plane. The tip is lower than the base of the hook. Carefully done, experiment a bit, you should be able to engage the tip and then, rotating the hook, get the rest of it under the screw for a good connection.
Whatever you do do not use the device to carry the feedthrough neutral current to any downstream loads. Pigtail. Breaking the neutral in a shared neutral situation, particularly a three phase one and one with unbalance loads can lead to violent fluctuations in voltage, equipment damage and fire. This is another reason I don't like a shared neutral situation in anything other than a well supervised industrial setting. This single issue, IMHO, makes potential harmonics problems look like a minor annoyance.
A lot of people, including some EEs, picture large savings in sharing a neutral on branch circuits. In my experience the savings usually fail to materialize in any great amount.
Dear 4,
Sorry to mislead. This was 3 phase for a commercial project.
~PeterView Image
We do a lot of shared nuetral wiring because commercial modular furniture systems are designed for it. Most of the modular office panels are wired for three 120v 20 amp circuits using #12 for the three hots and a #10 neutral, with a #12 grnd. Makes for some interesting trouble shooting at times, but really no major issue when wired correctly.
Dave
Exactly. "no major issue when wired correctly"
And it remains wired correctly. When was the last time anything remained wired correctly for long. Many plants are hiring glorified handymen, no insult intended to any handymen our there, instead of trained electricians.
Didn't mean to sound like three phase shared neutrals were a disaster but they are an added hazard. No big thing in an industrial setting but more danger than necessary for residential work.
Harmonica are another issue. Harmonics have been a buzz word for the electrical community for some years. While a few cases require careful engineered solutions and fairly complicated analysis the vast majority are simple cases of poor design, failure to upgrade as loads are shifted and basic maintenance or upkeep.
The oversized neutrals can, in a small number of cases, solve real problems but mostly it just seems to be a substitute for proper design and a trend. No need to calculate if it is actually needed. Just throw it in so you sound special. Adds to the mystique of electricity. The electrical contract gets a bit bigger, contractors is happy, and the buyer, not knowing anything about harmonics, shuts up and digs deeper for something he doesn't need.
`scuse the ignorance, but what`s IMHO?
IMHO is internet slang for "In My Humble Opinion."
tanks from a `net luddite
In My Humble Opinion
(secret breaktime code)
"Breaking the neutral in a shared neutral situation, particularly a three phase one and one with unbalance loads can lead to violent fluctuations in voltage, equipment damage and fire."
4Lorn1,
Ain't that the truth. A coworker of mine recently detached a "common neutral" in his house (without turning off the breakers), causing all the shared circuits to go from 110V to 220V. Blew out nearly every electronic appliance in his house. At least the day old, big screen TV was still under warranty.
Jon
"Many of these screws ... are plated steel."
Dang! Another belief reduced to the rubble heap of myth. Next I suppose you'll claim that the "Silver" screws are not made of real silver. I always thought they were, since silver is the best conductor, so I always made it a point to collect them from discarded receptacles. Sometimes I would get bored in a jury lounge or hotel room so I would take my screwdriver and pull the receptacles out of the wall. Often only one silver screw would be used so I removed it and kept it. I now have about 450 of them and now you say they're useless!
~Peter
"These movable plates are used to clamp solid wire, no stranded need apply,"
I had never heard that about stranded wire.
I would looking at Cooper BR-15 and BR-20 and Leviton BR-20's and 5252/5352's today.
The Cooper's had marded on the back next to the holes #14-#10 AWG CU.
The Leviton's had the same information printed inside the box.
Neither place did they limit it to solid wire.
When I worked for Northern Electric (1960's) we were taught to never back out the screws, but to cut a passage in the down-side of any ring terminator if you needed to attach one.
I have no idea if there's any science behind these instructions, or if there were other consideration, but that's they way they wanted it.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
Funny you should mention removing a piece of the ring terminal - last time I looked for hook terminals I wasn't finding them readily. 3M doesn't even make them. Cutting away part of a ring terminal worked for me in that particular case.
"When I worked for Northern Electric (1960's)"
Phil,
Not to highjack a thread, but ....When talking about tides, you mentioned that you helped build/work on the bridge over The Bay of Fundy (known for having the greatest tides in the world). When talking about the history of operating systems, you were working at IBM and had inside knowledge of OS/2 development at the time. Is there anything you haven't done?
Jon
I was positive this thread was going to be about me.
Live, Love, Forgive and Forget
quittintime
Is your back hurting you? :(