Back Wired Switches Question ?

Either the "pressure plate" or the screws is fine; same difference. Don't use the holes. The 'spring loaded ' design you're imagining is more of a knife edge that digs into the wire. think about the difference between the contact area of a knife edge versus the surface area of a screw head. The latter is obviously the better contact. The former will generate more heat and hasten failure under significant loads.

John

"John Ray" wrote in news:C6H6e.42237$ snipped-for-privacy@twister.southeast.rr.com:

Agreed, and as another pointer, if you use the screw only type, remember to wrap 80%. (Wrap the wire around 80% of the screw dia)

I agree and have never trusted poke-in connections. All the posts I have seen also agree. However they must be covered by a UL standard and devices must be physically tested to the standard. Any idea why the discrepancy?

John Ray wrote:

From: snipped-for-privacy@isp.com (Bud) I agree and have never trusted poke-in connections. All the posts I have seen also agree. However they must be covered by a UL standard and devices must be physically tested to the standard. Any idea why the discrepancy? John Ray wrote: Either the "pressure plate" or the screws is fine; same difference. Don't use the holes. The 'spring loaded ' design you're imagining is more of a knife edge that digs into the wire. think about the difference between the contact area of a knife edge versus the surface area of a screw head. The latter is obviously the better contact. The former will generate more heat and hasten failure under significant loads. ~~~~~~~~>

I say: In my experience there is nothing wrong with those push-in devices., I've also noticed that most of the electricians that are opposed to using the push-in contacts are the ones that been wiring things up before they came up with the push-in contacts., it's almost like some of them resent anything New in the Trade that makes the job easier.sheesh :-( for petes sake., they also like to put trainees & journeymen through it regardless.

although I agree to using the screw contacts for circuits where motor cycles or tension may tend to pull on wires more than nominal operation., if they are UL approved, available and convenient, why not use them ? I do ., it's much easier than toiling with dozens of screw terminals and I have no doubt when done properly with due care, it allows for a safe & effective installation.

=AEoy

Good advice, I have to remind myself sometimes, don't let the wire crawl out from under the screw. Keep it totally under the head.

later,

tom @

Metal fatigue. The push in connectors work great and pass whatever tests when new. But with heating/cooling/aging over the years, the spring tension decreases and the connection becomes less reliable.

Ed

Wrap clockwise around the screw too. So tightening the screw tends to draw the wire in and around, not push it out.

daestrom

I think the overheating is a big part of it. Heating the 'spring' tends to anneal the metal and lose it's 'springiness'. So less force is holding onto the wire.

daestrom

Agreed. The ones that fail are invariably on circuits where they are subjected to heavy current draw. I've never heard of one that failed when all it did was supply a small table lamp or floor lamp.

Ed

I've found dozens. Back when I did service calls. Though the problem was usually compounded by the installer using both stabs to make the splice.

John

Always clockwise. Just talking about the drop peeking out. So I hook, loop, and pull slightly to keep the top against the shaft, while turning.

later,

tom

I think the problems are real. So I don't understand why UL, which if I remember right is/was tied to the insurance industry, wouldn't be aware of problems in actual field use and modify the standard.

John Ray wrote:

UL is about human safety. If that back stab connection fails, is it a threat to human life? No. Therefore approved. If that back stab connection is a threat to computer data: not the domain of UL. Perspective. For what the UL addresses - those back stab connections are just fine.

Always first ask what the perspective is for that standard. UL is about human safety. UL approval does not even care if the appliance is reliable or even does someth> I think the problems are real. So I don't understand why UL, which if I

OK.

Explain how a "back stab" connection could develop some significant resistance and NOT become a fire (that thus human life) threat.

I suspect that in the real world. "loose" screws cause many more problems than "back stab" failures.

I can only speak from experience. For about 3 years I was a residential service tech. Of course ANY device can fail, but I would say that at least

95% of device failures I experienced were due to back stab installations. Except for the REALLY old stuff, the 'fire' is actually more of a 'baking' resulting in case deterioration, not open flame. Once the case becomes brittle enough to fail, the conductive parts either trip the circuit or fall open. Usually, though, the arc point fails before that can happen. I've actually found devices that would read continuity on the Fluke, but would NOT pass current under line voltage.

I have found a few loose screw probs, but literally a few. I think anyone who is going to take the time to use the screws rather than the stabs is going to properly torque the screws.

John

Good observation.

later,

tom @

"John Ray" wrote in news:Qds8e.71424$ snipped-for-privacy@twister.southeast.rr.com:

I too, in my years of residential electrical work, have found many instances where the back stab connections have failed. As you mentioned, typical visible conditions when exposed are baked, brittle housings, significant arcing evidence and loss of all tension on the wire. Many times, soot can be seen inside the receptical box, along with major sooting/melting of the wire and insulation near the stripped portion of wire, indicating a significant flash has occured. I have never used the back stab connections for this reason. I do not trust them. In an industrial setting (control panel, etc) where the end load is known and fixed, use of spring type connections would be ok, in my opinion. In a residential setting, where end load is really unknown, I do not like them. If a user can do it...it will be done at some point. It seems that, from what I have seen in the field, high-load heat cycling contributes significantly to the problem. I am really curious if the smaller contact area between the wire and spring clip vs. a screw contributes to the problem. Most of the spring clips within recepticals I've seen are a punched v shape, in which due to the angular contact with the round wire, would only produce only two small contact areas, whereas with a properly assembled screw connection, you have more surface area in contact with the wire.........dunno....

I've never come across a malfunctioning back wired device... nevertheless, I've removed many and I too prefer attaching the wires to the screw terminals instead... you never know where people want to plug in a small space heater other unforseen load.

I have taken the wires out of them by spinning it either clock/or counterclock wise, they do not come out that easy, though some have a small stab slot suggesting it's easier to remove prying there, it can damage the tension inside the connector.

Like a told my last assistant, Electrical Devices and Equipment is finer and lots more delicate than it looks....Give it to a Technician to find it out with minimal damage, anyone going to hard on any of them could lead to permanent irreversible damage and cost you pricey replacements or refitting.

Roy