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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"

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    \$\begingroup\$ 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. \$\endgroup\$
    – Justme
    Commented May 23, 2023 at 19:05
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    \$\begingroup\$ You will need a strain relief \$\endgroup\$
    – Andy aka
    Commented May 23, 2023 at 19:18
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    \$\begingroup\$ 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. \$\endgroup\$
    – vir
    Commented May 23, 2023 at 19:39
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    \$\begingroup\$ Do yo really mean screw terminals? Or do you mean terminal blocks? \$\endgroup\$
    – Davide Andrea
    Commented May 23, 2023 at 19:45
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    \$\begingroup\$ 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. \$\endgroup\$
    – SteveSh
    Commented May 23, 2023 at 21:58

2 Answers 2

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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

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    \$\begingroup\$ 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. \$\endgroup\$
    – Noideas
    Commented May 25, 2023 at 7:53
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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.

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    \$\begingroup\$ 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". \$\endgroup\$
    – Davide Andrea
    Commented May 23, 2023 at 22:37
  • \$\begingroup\$ C. Dunn - Hi, Please remember the site rule 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. \$\endgroup\$
    – SamGibson ♦
    Commented May 23, 2023 at 22:38

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