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wire nuts

Discussion in 'Electrical Engineering' started by E Z Peaces, Sep 11, 2009.

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  1. E Z Peaces

    E Z Peaces Guest

    Before 1975 I preferred to splice with solder. Then I came to love wire
    nuts: easier to use, less to go wrong, reliable, usable where I couldn't
    get both hands, and undoable without tools.

    About 1982 I discovered the B-cap. Apparently the only advantage was
    that the spring would expand more than some designs. It meant one size
    would work for most connections I needed, it seemed to grip more
    securely, and it was easier to get it to encompass all the ends of my

    As I clipped some shrubs, I snipped the cord of my expensive headphones.
    Those silky copper strands looked impossible to splice. I used
    masking tape to splice each of the three conductors, then screwed a
    B-cap over the whole thing. It has been trouble-free for years. I'd
    call the B-cap a versatile wire nut.

    I think they came in B1, B2, and B4. They were on Ideal's website a
    month ago. Now I don't see them. Has the B-cap been made obsolete?

    A neighbor prefers Scotchloks and crimped butt splices for his big rig.
    Most of his electrical problems seem to come from old Scotchlok
    connections, and they can be tricky to use even with two hands.

    Over the years, I've often had wires pull loose after I crimped a butt
    splice. On my neighbor's truck, mechanically strong butt splices may
    feel warm in use.

    Are Scotchlocks or butt splices or other methods somehow superior to a
    good wire nut properly applied?

  2. I think that you may merely be nuts over wires. Nice title. :)

    Anyway, good luck finding what you are after.
  3. The title should have been wire soup to nuts:)
    Anyway, in EU (Greece) we ue exclusively wire nuts, never heard of the other
    things you use. I doubt whether they ever used solder, though.
  4. TheJoker

    TheJoker Guest

    In your case, the trick would be to open your skull cavity, and cut the
    three nerves between the two halves of your brain (if they are still
    there, and if you have them to begin with)(your behavior makes it
    impossible to tell).

    Then, you would be less spliced, and less twisted, tightly or

    Then the electro-shock sessions could start.

  5. They were never popular or common in the UK, and were
    completely displaced by more reliable mains connectors
    by the late 1930's. They were called "Screwits" here,
    not wirenuts. They were in effect made illegal in 1960's,
    as they'd never got British Standards approval, which
    became mandatory for wiring accessories at that point.
    However, they were long gone before then anyway.

    They continued to be used for very low voltages (e.g.
    door bells, radio receiving aerials) through to the 1950's.

    Just for confusion, there are a couple of connectors
    here which look similar and can be confused with wirenuts.
    The first is a crimp in which the metal insert is crushed
    onto the conductors through the plastic casing. The second
    (no longer used in exactly the same form) was a bit like a
    wirenut, but had a couple of grub screws in the side to
    clamp the conductors in the internal brass insert, and was
    very commonly used in 1920's through to 1950's.
    These were the forerunner of the current chocolate block
    connectors, which have the same brass inserts and are
    very commonly used today.
  6. James Sweet

    James Sweet Guest

    I've had some quite extensive discussions on this topic with an EE
    friend in the UK, and after sending him a few of our wire nuts, he says
    they're much better than those available in the UK. As for which forms a
    better connection, the UK style terminals or US style wire nuts, it's
    pretty much a toss up, both are very reliable. Installed correctly, the
    wire will usually break under tension before the wire nut will come off.
    It's extremely rare for them to cause any trouble at all.
  7. In which case your friend was clueless about requirements for
    cable conductor termination in the UK and how they came about.
    That's not what the stats say about them.
  8. E Z Peaces

    E Z Peaces Guest

    I can imagine voting to outlaw them.

    I was an electronics technician in the Coast Guard. Whatever method I
    used, it was important to test my workmanship by tugging each conductor.

    I didn't use wire nuts in my duties but did use them to connect lighting
    as the manufacturer instructed when I installed a fairing on my
    motorcycle. A reliable headlight connection was a matter of life or
    death, and a short could have been disastrous in a system without fuses.
    In 36 years of vibration and moisture, I've had no trouble with those

    In 1976, the vestry at my church asked me to rewire a dozen old lights
    that hung on chains in the nave. The old wiring used solid conductors
    with twisted connections wrapped in cloth tape. The connections had
    worked for decades and were mechanically sound when I removed the tape.
    Workmanship counts.

    The box of wire nuts said, "No need to twist wires." I found that the
    finely stranded conductors I was using would twist CW as I screwed on a
    wire nut. As a result, I would feel movement when I tugged. With this
    kind of conductor, if I twisted CCW before applying the wire nut, its
    threads would get a better grip on the conductors.

    After I agreed to do the job, I was told the junior warden's sons would
    assist me. I was uneasy. On ladders, we couldn't work together. I'd
    have to trust their workmanship.

    I explained the importance of testing a connection by tugging the
    conductors. I told them I'd found that in this case a wire nut would
    hold better if the conductors were twisted CCW.

    They had wired several lights when the senior warden dropped in. They
    complained that I had told them to twist the conductors CCW. He was not
    an electrician. He sold lumber. He told them I was wrong and they
    should twist CW. For years, my responsibilities had included reliable
    connections. I was supposed to be in charge, but neither my assistants
    nor the warden consulted me.

    Apparently the boys had disregarded my instructions and now they wanted
    the warden's support. If they thought their method was okay, they had
    not been testing their connections. Such indifferent workmanship would
    explain why it was common to tape over wire nuts.

    If connectors had to be foolproof, I would have outlawed wire nuts.
    However, this was not the Coast Guard or a motorcycle. Nobody's life
    depended on the connections. They were in proper enclosures and the
    circuits had breakers. I suppose that's why Underwriters' Laboratories
    approved wire nuts.

    My BIL once worked for an electrician who showed him how to twist
    conductors CW with pliers, snip the ends even, screw on a wire nut, and
    tape. He rewired his house as he remodeled. Then he asked me to make
    some improvements.

    I found his connections mechanically sound when there were only two
    conductors. With four or five, I felt movement. I found that if I laid
    the ends parallel without twisting, I could get solid connections; but
    it was hard to get the ends of several conductors even and sometimes it
    would take more than one try to get a mechanically sound connection. In
    these cases, modern live-spring wire nuts were much more foolproof.
  9. Rich.

    Rich. Guest

    I find it disturbing that a guy who sell lumber knew better than you how to
    make a splice correctly. The problem with your method is that the expansion
    and contraction over time allows the wire nuts to loosen and they fall off
    when someone moves the splice around. Wire nuts are UL approved only when
    the splice is twisted CW for a reason.
  10. Mycelium

    Mycelium Guest

    The effect is known as "bird caged". CCW twisting in cable assemblies
    causes problems as well, and I hate having to explain to a contract
    vendor their own job of the details of making a simple cable harness.
  11. E Z Peaces

    E Z Peaces Guest

    Can you cite that?

    Every box I've bought says "no need to twist" or instructs the user to
    hold the ends straight. Do these manufacturers ignore the UL?

    None of my splices end up with a CCW twist. The stranded conductors
    with the thinnest, most flexible strands are the ones I start with a CCW
    twist (less than one turn) and they end up with biggest CW twist. In
    twisting from CCW to CW, they pass through being straight, and that's
    when the tapered threads can best squeeze them all together.

    If I intend to open and remake a splice of very flexible conductors,
    I'll tin the ends and lay them straight as the instructions say. I've
    read about a third method. Instead of tinning, simply twist each
    conductor for stiffness, then lay them straight as the instructions say.
    I haven't had a chance to try it because it has been years since I
    spliced conductors with fine strands.

    If the UL says conductors must first be twisted CW, I wonder why the
    electrician who taught my BIL to do that also taught him to apply tape.
    I often found insecure connections when I removed the tape. If I
    redid such a splice according to the manufacturer's instructions, no
    conductor would budge when I tugged. A good tight mechanical connection
    is less likely to heat up.

    When and where did the UL say conductors must first be twisted CW?
  12. E Z Peaces

    E Z Peaces Guest

    Where can I read about this effect?

    With straight conductors and a properly sized wire nut, tightening will
    cause a gradual increase in friction like a pipe with tapered threads.
    To me, that says the contact area between conductors is increasing (to
    handle current better) and the wire nut is less likely to come unscrewed.

    I've never liked the feel if, contrary to manufacturer's instructions, I
    start with a CW twist on the conductors. I don't get that gradual
    increase of friction.

    The strands of ordinary stranded wire such as would be used for
    automotive lighting, are stiff enough for me to lay the conductors
    straight, like solid conductors.

    Lamp cord may be so flexible that friction from turning a wire nut can
    twist it to the point where it bunches up; the twisting of the
    conductors increases the diameter before the wire nut can compress them.
    In order to be threaded inconspicuously along the chains, the wire for
    the church lights was flexible like that.

    I was like the boys in that intuition told me to stiffen the conductors
    by twisting slightly CW. I tried it several times and it was
    unsatisfactory. That pretwist caused the bunching to start sooner.
    Instead of increasing friction, I'd feel wire twist and the nut jam.
    Tugging the conductors would help untwist the copper, reducing the
    diameter and causing one or both conductors to come loose.

    That's when I tried half a turn CCW. It stiffened the conductors but
    shortened them only about 1%. When I did it that way, I felt the wire
    nut tighten gradually as with solid conductors, and my connections
    resisted tugging. I believe it works by letting the clamping action of
    the wire nut get a little ahead of the expansion caused by the CW twisting.
  13. E Z Peaces

    E Z Peaces Guest

    I've been trying to find out about a UL requirement for pretwisting.
    Pat Porzio is an electrician who says,

    "For a connector to be UL-listed, it must make a firm splice without
  14. I guess in most countries the experience of the trades person counts for a
    lot, unfortunately this seems to be a 'fast track area' these days.

    Cheers .......... Rheilly P

  15. Generally, the effect of twisting one on causes a CW twist in the bunch
    being grappled.
  16. Rich.

    Rich. Guest

    I never said anything about pretwisting, you did. I said that wire nuts are
    UL approved for CW twists, as opposed to your CCW twist application. When an
    untwisted splice is inserted into a wire nut and the wire nut is twisted,
    the splice ends up with some degree of a CW twist to it. So at no point
    during the installation of the wire nut does the splice develop a CCW twist.

    Even this article you posted the link to states, "Next, hold the wires
    firmly together with the stripped ends parallel (step 1). Press the
    connector over the wires. There should be no exposed conductor (step 2).
    Twist the connector clockwise and stop when the splice is tight (step 3)."

    Your own article states to start with the wires parallel, not a CCW twist.
  17. James Sweet

    James Sweet Guest

    What stats? What sort of wire nuts? Cite source.

    I have here a nice assortment of UK terminal strips and other hardware,
    it works well and I like the terminal strips for wiring stuff up in
    equipment I build and various temporary setups.

    I also have US style wire nuts as they're the standard method for
    joining wires here. There are millions and millions of them in daily use
    throughout the country, and I stand by my assertion that properly
    installed, they form a very strong, dependable connection. The tapered
    spring insert cuts slightly into the solid copper conductors and twists
    them together as the nut is applied. Again, these are good quality name
    brand parts I use.

    I cannot speak for the wire nuts available in the UK as I've never had
    any, but according to my only source on this, they are not particularly
    good, and have never been popular.
  18. E Z Peaces

    E Z Peaces Guest

    Where does the UL specify twisting conductors clockwise? Don't they
    test connections after following manufacturers' instructions? The
    instructions I've seen don't say the conductors must be twisted before
    or during application of the connector.

    In his patent drawings, the inventor of the wire nut showed no twisting
    of conductors before or after application of the connector. It was a
    live-spring device, my favorite type. The spring conformed around the
    conductors, squeezing like a boa constrictor with several convolutions.
    In my experience, if I use a live-spring wire nut with large, solid
    conductors (such as #12 or #10 with a nut sized for #10 maximum), it
    will probably tighten fully without twisting the conductors.

    In my experience, fully tightening a rigid wire nut will twist the
    conductors. Twisting expands the diameter of the bundle of conductors
    to wedge against the tapered threads. In my experience, a rigid wire
    nut will squeeze more tightly and be more securely affixed if it becomes
    tight with only a little twisting of the conductors.

    I think I understand why. If conductors are twisted slightly, so that
    they are nearly parallel to the axis of the nut, twisting 1/2 turn will
    expand the bundle diameter only slightly. That's analogous to
    tightening with a fine-thread screw. If the the bundle is more twisted,
    twisting another 1/2 turn will expand the bundle more rapidly, like
    using a coarse-thread screw. Turning the wire nut won't compress the
    bundle as tightly, and the nut will be less secure.

    My BIL pretwisted his wire-nut connections as he'd been taught working
    for an electrician. If he was connecting 4 conductors, he'd strip 2-3",
    IIRC. The need for all that bare wire showed that the twisted bundle
    had a much bigger cross section than 4 straight conductors, so it
    wouldn't go as far into the wire nut. Twisting such a fat bundle meant
    the conductors weren't nearly parallel to the axis of the wire nut; that
    meant further twisting for a tight fit wasn't very effective.

    That explains why the electrician's method required tape to secure the
    nut. Tape was necessary for another reason. One had to estimate how
    much insulation to strip before pretwisting a certain number of
    conductors. This could result in bare copper extending beyond the skirt
    of the wire nut. The method was apparently adequate for household
    wiring, but I would not have wanted it in a vehicle, where connections
    are not enclosed in boxes and are subject to vibration and tugging.
    Using solid conductors, I'd do it just like the example. I'd even add
    those twists in the insulated conductors as a measure of protection
    against tugging.

    He says he doesn't pretwist because he wants to be able to undo his
    connections easily. That sounds like saying the strength of a
    connection comes from the clamping of the nut and not the twisting of
    the conductors. I agree.

    Good workmanship requires making sure a method works in a particular
    case. The instructions for the wire nuts my BIL used said nothing about
    tape, but the electrician who taught him had found that tape was
    necessary to use a wire nut on a pretwisted bundle.

    I found that the finely stranded conductors at the church twisted too
    easily for the wire nuts to screw on properly. I didn't feel a gradual
    increase in friction as I turned, and the conductors could be tugged
    loose. I could get good mechanical connections if I twisted the
    conductors CCW in order to give the wire nuts a 1/2-turn head start on
    the CW twisting of the conductors.

    The boys may not have known how a wire nut should feel as it screws on,
    but they would have found the results of CW pretwisting unacceptable if
    they had tugged each connection as I instructed. The boys and the
    warden used the easiest method to put the wire nuts in place. It was
    not what the manufacturer said or what I had found, and they must not
    have tested their connections.
  19. James Sweet

    James Sweet Guest

    I don't twist the conductors first. I strip off about 1/2" of
    insulation, line up the tips of all the conductors, then screw the wire
    nut on clockwise which then slightly twists the wires together as it is
    tightened up. No tape is necessary, although I normally use a bit on #10
    and heavier wire just to provide a bit more mechanical strength with the
    stiff wire. I have yet to ever have a bad connection, although I've
    repaired many poorly done and problematic splices done by others. My own
    experience suggests that if you twist the wires up first, the wire nut
    is not nearly as secure as it is if the metal insert screws onto
    straight wires. The insert is harder than the copper and actually cuts
    threads into the solid conductors, this is why the joint is so strong.
  20. E Z Peaces

    E Z Peaces Guest

    I've had #10 wire make a rigid wire nut feel like it wouldn't fully
    seat. I've also had the problem with #12 wire that had been hardened by
    twisting and untwisting from another splice. A live-spring wire nut
    worked better in those cases.

    It was 25 years ago that I was splicing stiffened wire. It didn't occur
    to me to secure wire nuts with electrical tape because I'd lost faith in
    the stuff. I'd bought several rolls from an electronics place, but
    after I taped a connection, the adhesive would eventually "melt" and the
    tape come loose.

    This left me wondering how I could predict that a roll of electrical
    tape would be reliable. After some years, I bought a roll of good
    stuff, but by then I was out of the habit of using electrical tape.

    Tonight I looked at that good roll. The cardboard core is marked UL.
    Why didn't I think of that 25 years ago!
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