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I have been using mounting blocks to connect wires (typically coming from sensors/supply battery) to my PCB.

The problem is, these do not seem to be robust. The wire often gets out of the block, which is not what I normally want to happen.

My guess would be to directly solder the wire to the PCB, but was wondering if anyone has another suggestions.

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    \$\begingroup\$ "Often the wire got out of the block" How do you mount the cables in them? What kind of termination / splice do you use? How does your stress relief look like? \$\endgroup\$
    – asdfex
    Commented Feb 17, 2023 at 12:28
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    \$\begingroup\$ What gauge wire are you using? Often this sort of connector is designed for use with wires above a certain size and won't grip very thin ones. \$\endgroup\$ Commented Feb 17, 2023 at 12:28
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    \$\begingroup\$ @cobdmg Is the terminal block appropriately sized for the wire? They can accept a wide range of wire sizes, but you may have trouble with a very small wire in a very large terminal. Is the screw fully tightened? Is the wire on the right side of the clamp plate? Remember, turning the screw clockwise should tighten it; if it tightens down on the wire when turned counterclockwise you've put the wire on the wrong side of the clamp. \$\endgroup\$
    – Hearth
    Commented Feb 17, 2023 at 18:22
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    \$\begingroup\$ Full data on that block can be found here. Are you using it within specifications? Not explicitly mentioned there is you really should be using wire ferrules on your wires when using them, as is industrial standard. \$\endgroup\$
    – Mast
    Commented Feb 18, 2023 at 8:25
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    \$\begingroup\$ You might also find "molex style" connectors a good option – they're easy to crimp onto wires, present in most PCB design libraries, come in locking or non-locking variants, and cheap. Not quite as simple as ferrules & terminal blocks, but have the advantage that you can connect and disconnect multiple wires (I suspect you want at least two!) very quickly and easily. \$\endgroup\$
    – Landak
    Commented Feb 18, 2023 at 13:36

4 Answers 4

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The problem with those screw terminals as well as soldering directly to the PCB is that any movement or bending of the wires will quickly lead to fatigue failure. A good solution would be to crimp bootlace ferrules on wire ends before screwing them into the terminal block or providing some form of strain relief for wires soldered directly to the PCB. Both of these solutions are good at avoiding wire fatigue and breakage.

You can also try using a bit thicker multistranded wire screwed directly into the terminals (do not tin with solder first as this increases fatigue failure rate).

Bootlace ferrules

Wire strain relief

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    \$\begingroup\$ if you weave through 2 holes the glue is not needed. \$\endgroup\$ Commented Feb 18, 2023 at 12:06
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    \$\begingroup\$ @Jasen it is if you want to respect the minimum bending radius, as indicated in the image. (I know, people don't respect that in practice) \$\endgroup\$
    – BrtH
    Commented Feb 18, 2023 at 16:56
  • \$\begingroup\$ (There is a notable difference between going through an even number of holes and an odd one.) \$\endgroup\$
    – greybeard
    Commented Feb 19, 2023 at 6:43
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If used properly, terminal blocks are very reliable. If they weren't, they would not be in such wide use in the industry. That is why I suspect you may not be using them properly. Rather than suggesting a different component, I suggest you stay with a terminal block but pay attention to its use.

Make sure that:

  1. You are using a wire gauge that is within the spec of the terminal block: not too small, not to large
  2. The end of the wire is flat and perpendicular with the axis of the wire
  3. The wire strip length is appropriate for the depth of the opening in the wire cage: just a few mm longer than the depth
  4. The wire cage is wide open
  5. The wire is fully inserted
  6. The screw is fully tightened

For increased reliability, consider crimping the wire to a terminal before insertion. These terminals are appropriate:

Pin, ferrule, and blade

{Digikey}

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    \$\begingroup\$ I have occasionally seen/heard people suggest that spring-loaded terminal blocks are "better" (less prone to under/overtightening, can deal with things shifting a bit over time), but I don't have first-hand experience. \$\endgroup\$
    – mbrig
    Commented Feb 17, 2023 at 20:52
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    \$\begingroup\$ You are correct: spring loaded terminal block are compliant and adapt to dimensional changes in the wire. Screw terminal blocks may or may not, depending on the design. \$\endgroup\$ Commented Feb 17, 2023 at 22:45
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    \$\begingroup\$ Those digikey llinks could rot rather quickly. It would be best to complement them inserting in your answer an image for each product. \$\endgroup\$ Commented Feb 18, 2023 at 21:08
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    \$\begingroup\$ Thank you. Done. \$\endgroup\$ Commented Feb 18, 2023 at 22:15
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The other answers seem to be concentrating on the ends of the wires. I suspect the problem here may be that the entire wire - or group of wires in a cable - is pulling away from the board. The solution to that is some sort of clamp or strain relief. This is a purely mechanical (not electrical) device and could be anything from a simple plastic cable tie looped around the cable through a hole in the PCB to a clamp installed in the product case to any of a number of other things. But the basic idea is to hold the wires or cable tight some distance from the electrical connection in a place where there will be no stress at all on the electrical connection except during assembly or repair.

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In addition to what has already been said, here are some common beginner problems with terminal blocks:

  • In case of screw terminals there's an "elevator" of sorts which you move down towards the wire when screwing. In case you manage to get the wire on the wrong side of this "elevator" then you get a poor electrical and mechanical connection since it's not meant to go on that side.

    This might be the problem you are experiencing. To avoid it, ensure that the screw is opened up all the way before inserting the wire.

  • Pressing the "elevator" down onto the cable insulation will give real nasty problems. This might give a nice mechanical connection and it's hard to spot. But the electrical connection will just be random and completely unreliable. Obviously the "elevator" should press against the exposed copper or ferrule. Using ferrules is also a good way of avoiding this common problem.

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