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What type of electrical contact joint is this?

  1. Mar 15, 2019 at 8:52 AM #1

    Wrichik Basu

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    While working on an old electric iron, I found this joint in the wires:

    20190315_190536.jpg

    Any idea what this joint is? Does it have a special name?

    The wires are in a horrible condition, so I have to change them. How can I build this joint by myself? Or are such wires readily available in the market?
     
    Last edited by a moderator: Mar 15, 2019 at 10:42 AM
  2. jcsd
  3. Mar 15, 2019 at 8:59 AM #2

    phyzguy

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    The metal piece is called a spade lug. It comes with the part on the left opened up. You slip the wires into the open part on the left and then crimp it shut. For better reliability you can then solder it together if you like.
     
  4. Mar 15, 2019 at 9:05 AM #3

    Wrichik Basu

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    Thanks.
     
  5. Mar 15, 2019 at 9:29 AM #4
    Its called a double crimp spade connector.
    One crimp captures the insulation the other crimp captures the bare wire.
    Those in your image were poorly made.
    The one on top has the wire too far into the crimp, while the one on the bottom does not have the wire sufficiently into the crimp.
    The insulation should be cut to just protrude through the first crimp, and the bare wire should protrude just through the second crimp portion.

    In the US these are available at any hardware store or electrical supply, along with the proper crimping tool.
    These can be crimped using other tools but, there is a special tool designed to make sure these crimps are made correctly. Care should be taken to not over-crimp the one holding the insulation; and to tightly crimp the bare wire for good contact. The portion of the bare wire may also be soldered to the connector after crimping if desired, to insure a low resistance contact.

    BTW- If that wire is subjected to intense heat, a high temperature insulated wire should be used; not a rubber compounded insulation.
     
    Last edited: Mar 15, 2019 at 9:39 AM
  6. Mar 15, 2019 at 10:04 AM #5

    phyzguy

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    Thanks for clarifying. I wasn't aware of the double crimp function.
     
  7. Mar 15, 2019 at 12:33 PM #6
    If the crimp is done properly (as noted, not like this one), then soldering does not improve reliability.
     
  8. Mar 15, 2019 at 1:02 PM #7
    Good point by @AZFIREBALL.
    TGGT (Teflon-Glass-Glass-Teflon) insulated wire ought to do.
    MGT (Mica-Glass-Teflon) can operate at even higher temperatures, but the mica makes it more fragile.

    Look for spade terminals made for high temperature operation. Regular ones are tinned copper; high temp parts are usually a nickel alloy.

    High temp connectors require more force to crimp correctly. Sophisticated tools featuring interchangeable dies and other amenities are available, but something along the lines of a Thomas & Betts model WT111M will do the job.
     
  9. Mar 15, 2019 at 9:25 PM #8

    rbelli1

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    If the crimp is done properly the soldering can actually reduce reliability.

    BoB
     
  10. Mar 15, 2019 at 10:15 PM #9
    Note there may be several different sizes of lug, and 'Murphy's Law' makes it probable those in a 'Handy Dandy Budget Set With Crimper Tool' will so be the other size...

    FWIW, as you've not used crimpers before, please get enough lugs to practise on your stock wire. Budget 'scissor' crimpers are okay in skilled hands, but a double-jointed ratchet model is far, far more reliable....

    As ever, 'Due Care, Please' ??
     
  11. Mar 16, 2019 at 4:47 AM #10
    Why is this? The only thing I can come up with is that the soldered part of the wire is stiffer, creating a stress riser where the wire is not soldered.

    I have also heard that soldered wire is not suitable for screw clamps, since the solder creeps under pressure and loosens the joint.
     
  12. Mar 16, 2019 at 6:57 AM #11

    256bits

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    What about tinning the wire before the crimp - recommended or not?
    Thanks.
     
  13. Mar 16, 2019 at 8:52 AM #12

    rbelli1

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    Exactly that

    The problem with that is that the solder is generally very soft so small stresses to the joint will cause additional changes to the shape of the wire. This will tend to cause the joint to wiggle loose. The copper wire will spring back from those stresses. This is the same problem with tinning wire before installing in screw terminals and using copper only screw terminals with aluminum house wiring.

    BoB
     
  14. Mar 17, 2019 at 12:40 AM #13

    davenn

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    these two crimps as shown, are extremely poor
    specially if carrying mains voltages/currents
     
  15. Mar 17, 2019 at 6:07 AM #14

    Wrichik Basu

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    Yeah, they are in very bad condition. The appliance itself is about 10 years old. The insulation of the wires is coming off the wires in bits and pieces. And yes, they are supposed to carry voltage from the mains. In fact, the neutral and the earth were shorted due to wearing out of the insulation.

    First I'll have to check whether the iron would work at all (testing continuity in the circuit of the heating element). Only then shall I put in new wires. Otherwise it will be a waste of money.
     
    Last edited: Mar 17, 2019 at 7:37 AM
  16. Mar 17, 2019 at 2:13 PM #15

    davenn

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    sounds like a good plan :smile:
     
  17. Mar 18, 2019 at 3:29 AM #16
    If it is about mains then just continuity won't be enough. You have to check if it is shorted to the casing/earth anywhere and if the resistance is still within range (both cold and hot). Also, you have to be sure that it is assembled properly, so it is still up to standards.
     
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