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Rare public involvement in electrical safety

  1. Mar 18, 2016 #1

    anorlunda

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    https://www.washingtonpost.com/grap...pid=hp_no-name_graphic-story-b:homepage/story

    I am impressed by this article in today's Washington Post. In my memory, this is the most notable case since the NASA Challenger O-ring disaster that attempted to make the public understand the mundane details of an engineering problem. The usual reaction to technical details about infrastructure is SNORE.

    Kudos to the WP for their excellent graphics. I recommend this article to all engineers as an example of good public communication.
     
  2. jcsd
  3. Mar 18, 2016 #2
    Excellent presentation! Most people don't realize how "close to home" dangers like this are. The same problems occur in ageing or damaged residential electrical systems. I just recently discovered a "back-stabbed" outlet which had a loose connection in my home. I just happened to notice excessive heat and minor smoke evidence from the unused outlet which had a high wattage heater further down the circuit. The defective connection was a serious fire hazard and the added resistance caused a large spike in power consumption. If the general public had more basic knowledge of electrical safety many tragedies could be avoided.
     
  4. Mar 18, 2016 #3

    sophiecentaur

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    What's one of those? (For the sake of UK readers, perhaps) Does it constitute a series or parallel resistance?
     
    Last edited: Mar 18, 2016
  5. Mar 18, 2016 #4

    anorlunda

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    backstab-outlet-holes-for-wires.jpg

    It is a way to terminate wires without screws. You push the bare end into the hole and it is held by a jaw that prevents it from being pulled out.

    Do you have those in the UK?
     
  6. Mar 18, 2016 #5

    sophiecentaur

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    I have never come across them, except, perhaps in a very naff lighting fitting. Interestingly, I did a Google search for the term and all the hits were non-UK sites. All the images involved US type outlets.
    When I included UK in the search criteria, there were no hits and definitely no images of 13A sockets and distribution panels with anything other than screw terminals.
    They sound pretty deadly for anything where there's going to be any movement involved. How do you re-wire them? Is it like barbed arrows, where you cut off the shaft and push them out of the other side of your leg? OOOOWWWCH!.
    Anyway, thanks for broadening my knowledge yet again.
     
  7. Mar 18, 2016 #6

    anorlunda

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    You're not the only one to have concerns sophiecentaur. This Old House says

    Backstabbed Wires What it means: On newer switches and receptacles, wires pushed in the back are more likely to come loose than those anchored around screw terminals.

    Code violation? No. The practice is allowed, even for new construction.

    Danger level: It depends. At a minimum, loose wires can cause a receptacle or switch to stop working. In the worst case, they can start a fire.

    Solution: Check for backstabbed connections by removing a switch or receptacle from its outlet box. If one is backstabbed, there are likely to be more. Release the wires and attach them to the appropriate screw terminals on the receptacle.
     
  8. Mar 18, 2016 #7

    sophiecentaur

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    I can feel smug about the very fussy regs in the UK. I can't imagine they would ever be allowed or anything other than very low power connections within appliances. Thoroughly nasty - yuc.
     
  9. Mar 18, 2016 #8

    jim hardy

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    I've troubleshot cheap "manufactured homes" around here and found numerous cases of lost connection at the backstab.
    If you're lucky it'll just fail and you lose everything downstream of the open. A neighbor lost outlets on one whole side of her house. Once i imagined the walls sans paneling it was easy to figure out how the electrician had run the "daisy chain". That one was particularly confusing because the open was in the neutral side. Giveaway was - in the "dead" rooms all the neutrals showed 120 to earth if anything was switched on..

    I refuse to use backstabs, myself.

    It takes a couple extra minutes to form the wires and put them under the screw terminals rather than just "strip and shove"(no prurience intended) . It's aggravating with #12 because it's so stiff , #14 is easy , but i won't use backstab on either.
    What's unsafe at 15 amps is unsafer at 20.

    I notice on newer fixtures that the "backstab" holes are too small for #12 wire. That tells me industry knows this was a bad idea to begin with.

    old jim
     
  10. Mar 18, 2016 #9

    Averagesupernova

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    20 amp backstab is no longer permitted in the USA. Many localities require outlets to be pigtailed. What this means is that the source wires have to be connected to the wires going out of the box feeding the next outlet in such a way so when the receptacle is replaced that connection is not interrupted. Usually this connection is made using the twist-on wirenuts. This of course eliminates a backstab connection, or a loose screw for that matter, in one box from causing problems in another box. For all I know, some localities forbid the backstab as well. The wire can be removed from a backstab by inserting a screwdriver that pushes the jaw out of the way which releases the wire. When outlets are not pigtailed it is conceivable that a 120 watt load on every outlet in the circuit will put a fairly heavy load on the first outlet. I don't believe the code dictates how many or few outlets are on a single circuit.
     
  11. Mar 18, 2016 #10

    wirenut

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    The NEC , for purposes of load calculations, treats a receptacle as 180 va (120vx1.5a) for general purpose plugs.
    If you have a 15 amp circuit the max is 8 (you only load a breaker to 80% of its value) so (15a/1.5a per rec.)x .80= 8 rec.
    For a 20 amp circuit you are allowed 10 (20a/1.5a per rec) x .8 = 10.6 so 10.
    Any good electrician will usually limit general purpose receptacles to 6 to 8 on a 20 amp circuit.
    Then there are exceptions for dedicated equipment and known nameplate loads.

    Back stabbing #12 wire has been against code for a long time, and if any of our guys backstab ANYTHING we know they are lazy and won't last long.
    In and around WNY almost every inspector requires pig tailing.
     
  12. Mar 18, 2016 #11
    To be more informative, I was alerted there was a problem due to the fact that with only one heater running on the circuit, turning my 40" TV on tripped the circuit breaker. I had previously ran two heaters, two laptops, the TV and a soundbar all on that one circuit without a problem. I may be mistaken but I think the problem can arise simply due to the small area of contact in the connection between the "jaw clamp" and the conductor. I had the same type problem with a microwave and a toaster in the kitchen, but that was due to a weak circuit breaker.
     
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