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2.54 Screw terminal blocks are a really convenient way to wire up devices without the need to solder a port or a jack connector.

However, with all their convenience, how reliable are screw terminal blocks really? Are they suitable for industrial-grade time use, i.e. 24/7/365 when the connected cables are allowed to dangle and sway a little bit?

A "little bit" in this case can be thought of as "how much a loose hanging Ethernet cable would sway inside a (non-technical) room where there is an occasional draft from door opening or a person passing nearby."

EDIT: Clarification - as pointed out by multiple commenters below, I should have said "terminal blocks" instead of "screw terminal"

Davide Andrea
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Noideas
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    How do you intend to terminate the cable to the screw terminal? Just strip away the insulation and shove it under the screw? What kind of screw terminal, will the screw just tighten the wire, or does it have an elevator design, or a spring leaf, or something else? And dangle a little bit is usually solved by fastening the cable to some fixed support with cable ties or something near the termination so it does not flap in the breeze. – Justme May 23 '23 at 19:05
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    You will need a strain relief – Andy aka May 23 '23 at 19:18
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    Cables aren't generally designed to be supported by the conductors. If you are concerned about the screw terminal coming loose, there are 2.54 mm spring terminals with a variety of actuation options but if you use strain relief like @Andyaka says then wiggling shouldn't be a problem. If you do end up with the screw terminals, make sure to torque them appropriately. Too loose and the conductor could fall out, too tight and you might break individual strands. – vir May 23 '23 at 19:39
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    Do yo really mean [screw terminals](https://connectorbook.com/classes/terminals_/board_terminals/board_screw_terminals/th_screw_terminals/i.jpg)? Or do you mean [terminal blocks](https://connectorbook.com/classes/terminal_blocks/pcb_terminal_blocks/pcb_screw_terminal_blocks/i.jpg)? – Davide Andrea May 23 '23 at 19:45
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    Like Anday aka said. Cables should always be supported and strain relieved, so that no movement of the cable is transferred to the contact/joint area. Depending on your vibration/shock environment (rocket launch), and the type of cable involved, multiple supports may be needed even over a short run of a couple of feet. – SteveSh May 23 '23 at 21:58
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    And your comment about "how much a loose hanging ethernet cable would sway inside a (non-technical) room where there is an occasional draft from door opening or a person passing nearby" really doesn't provide any data with which to see if a problem exists and to engineer a solution. – SteveSh May 23 '23 at 22:00
  • @Justme Termination is done via RJ45 male jack 120 Ohm terminator at the end of the bus. Attachment to the screw terminal is done via stripping the wire, twisting it around conductor then clamping it inside. Screw terminal is of the "just tighten the wire" type. Affixing cables so they dont sway may not be possible. – Noideas May 24 '23 at 02:31
  • @SteveSh It may not provide the engineering-grade explanation, but this is something an engineer responsible for installation WILL hear from some client eventually. Therefore, it is to be considered "engineer enough explanation" IMO, since this is the problem statement wording engineers have to deal with. – Noideas May 24 '23 at 02:33
  • @DavideAndrea Screw terminal blocks, such as this: [link](https://ae01.alicdn.com/kf/HTB19ZKEdhSYBuNjSsphxh6GvVXaz/Excellway-RJ45-Network-Adapter-8P8C-Crystal-Head-to-8PIN-Terminal-Rj45-To-Screw-Term-Block-Adapter.jpeg) – Noideas May 24 '23 at 02:35
  • Thank you. Now that that's clear, I edited your question and entered an answer. – Davide Andrea May 24 '23 at 02:51
  • What are the wires used for, are parasitics and skew an issue? (Ie, are you using them for unregulated power, or GHz video signals?) What sort of bandwidth and impedance control do you need? – user1937198 May 25 '23 at 13:52
  • @Noideas Is that solid or stranded wire? RJ45 makes me think of Cat5-type cable, which comes in both varieties. Solid wire is more susceptible to fatigue failure. – Andrew Morton May 25 '23 at 15:09
  • @AndrewMorton Stranded wire CAT5e cables. About 50cm long, most of which dangles free between two RJ45 endpoint connectors. – Noideas May 26 '23 at 05:27
  • @Noideas I wouldn't worry about it for just 50 cm of cable. It'd be better to use a cable tie and something like a cable tie base half way along to make sure it stays out of the way, but not entirely necessary. Have a look at the mess in [this article](https://www.ashtonsolutions.com/2018/09/11/cleaning-up-a-server-room-mess/) for an example of what the cables can cope with. Having said that, if it's an essential cable, maybe tie up a spare next to it. – Andrew Morton May 26 '23 at 10:22

2 Answers2

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We've used barrier blocks like the Molex 0387206202 in military applications without issue:

Photo of Molex 0387206202

Image source: Digikey - Molex 0387206202

To make the connection more robust we use solder-loaded heat-shrink ring terminals, which are similar to McMaster part number 9983K11 (the ones we use have adhesive inside the tube to prevent moisture intrusion). If you try to pull the ring terminal off, more often than not you'll break the wire before the terminal comes off.

To prevent the screws from coming out we'll use a medium duty thread locking liquid. Medium duty is still removable with a screwdriver. If additional environmental protection is needed, we pour goop (descriptive term, not a trade name) over the terminal block.

If wires movement is a concern, tie the wires down in multiple places. This is what is done on helicopters which are notorious for vibration.

Davide Andrea
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C. Dunn
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    That's a "barrier block", not a "terminal block". Terminal blocks have a wire cage, barrier blocks do not. OP asked about "screw terminals", which are single circuit, but I think they really meant "terminal blocks". – Davide Andrea May 23 '23 at 22:37
  • C. Dunn - Hi, Please remember the [site rule](/help/referencing) which requires that when a post includes content (e.g. text, image, photo etc.) copied or adapted from elsewhere, the copied content must be correctly referenced. As a minimum, the source webpage or PDF etc. should be linked (references for books / articles should include title, author(s), publisher, edition, page numbers etc.). In order to help you, I found what I believe to be an example of a source webpage for that image & added it for you. In future, please remember it's your responsibility to do that :) Thanks. – SamGibson May 23 '23 at 22:38
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I should have said "terminal blocks" instead of "screw terminal"

Thank you for clarifying.

Terminal blocks, especially 2-piece pluggable terminal blocks, are ubiquitous in industrial equipment, though not as much as DIN rail terminal blocks. They were designed for that application and have a proven record in that environment.

The friction between the two mates in a 2-piece pluggable terminal block is generally sufficient to prevent accidental unmating. If more assurance is required, terminal blocks with two screws are available.

A wire properly terminated in a wire ferrule and properly secured in the wire cage of a terminal block can withstand a pull force that exceeds the unmating force of a 2-piece pluggable terminal block.

All of the above should reassure you that terminal blocks are a reliable solution in industrial-grade use. Still, you may add a mechanical strain relief on the wires to absorb any pull force away from the terminal block, such as by tiewrapping the wires to a pull tab on the plug (see picture).

Phoenix Contacts MSTB 2.5-4-STZF-5.08

Source

Davide Andrea
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    Thank you, especially for mentioning the terminal blocks with pull-tab. These seem to be the good option if the cables have to be left dangling for some reason. – Noideas May 25 '23 at 07:53