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Spade lugs and screw terminals eliminate wiring rat’s nest

As the final stage of my “good deed” project in helping a friend install three heating-system smart thermostats, I felt obligated to clean up the incredibly messy wiring of the project. While I shouldn’t make excuses, this project didn’t start with the intention of being a poster for a “rat’s nest” project. Instead, there’s the usual excuse: it just grew out of control unintentionally.

The back story: We started the project with just one smart-thermostat zone in 2017 and the resultant wiring arrangement wasn’t very good, but it wasn’t too bad, either. But then we added another zone in 2018, and the final third zone in 2019. With each added zone, the wiring mess grew exponentially. This situation often happens at the engineer’s test bench, as a temporary hookup gets layered with more of these temporary and often poorly documented add-ons, and pretty soon, it’s a jungle of wires, patches, odd components, and more. Still, I couldn’t leave the thermostat wiring that way for three reasons:

  • if anything went wrong or needed to be upgraded, such a random-looking wiring mess would be a discouraging and even costly impediment for the debug or upgrade cycle, especially as heating systems usually malfunction at the worst time;
  • such messy wiring reflects badly on engineers in general;
  • it reflects badly on me, personally; neat wiring and thorough documentation are good engineering practice, and should be provided as part of the final package when you declare a project “done.”

My original plan was to use some sort of compact, multiline connectors to organize the wiring. After all, that would look very “up to date” and convey the impression that whoever did this wiring job knew his or her cables and connectors.

But after studying the problem some more, I realized that using trendy connectors wasn’t realistic, again for multiple reasons:

  • the wires were a mixed collection including #24 AWG solid and #18 AWG stranded, and no single, easily-obtained connector type can handle that range;
  • the reality of house wiring, and house “stuff” in general, is that it has to be viable for years and decades; who knows if one of these modern connectors will even be available in 10 or 20 years, or perhaps longer?;
  • one of the virtues of multiwire connectors is also their weakness: yes, you can connect a set of wires with a single connector, but trying to probe or disconnect any single wire in the connector is difficult, if not impossible, unless you have a “breakout” adapter.
  • finally, this wiring was going on a basement panel and there was a reasonable amount of space, so the compactness that a multipin connector offers isn’t really a needed virtue here.

I decided to go “back to the future” and use old-fashioned but easy-to-get crimpable spade lugs and screw terminals (Figure 1). I used these for both the main panel area (Figure 2), as well as the 24 VAC transformer area (Figure 3). (Note that here are three such transformers with one for each zone, and while a single transformer could easily handle all three zone loops, we ended up with three units due to the incremental nature of the upgrade. Plus, it means each zone is truly independent of the others and also provides a potential backup-power option if any of the three goes bad). Since low-voltage DC contact-closure and 24 VAC design, wiring, and connector bandwidth are non-issues.

photo of spade lugs and a terminal stripFigure 1 The spade lug made wire termination and connection easy, while the more-secure ring terminal was not needed here (top). When combined with a terminal (barrier) strip, making connection goes quickly – and test and debug is greatly simplified (bottom). Sources: K.C. Electronic Distributors, You-Do-It Electronics

photo comparing the old and new wiringFigure 2 The old three-zone wiring was a mess and something of which to be embarrassed if not ashamed (left), but the upgraded wiring has a large number of screw terminals which organized the wiring, eased installation, and enabled off-site pre-wiring (right). Source: author

photo of the old power strip layout

photo of the new power strip layoutFigure 3 Instead of one AC transformer mounted on an AC junction box and two others on a misoriented power strip, the new arrangement uses a horizontal power strip that has sufficient inter-unit spacing along with secondary-side wiring in the correct direction. Source: author

Another advantage of using spade lugs and terminal strips is that I could pre-wire most of the upgrade off-site at my workbench, and then finish up the remainder on site; that’s one of the reasons for what may seem to be the excessive use of terminal-strip connections in the photos. Pre-wiring is much faster and less error prone or awkward than doing it all while standing in a basement, even if that basement has decent headroom and lighting.

I’m happy to say it all came out just fine, and there’s a nice sort of pride of accomplishment in seeing all those shiny screw terminals and their spade lugs, as if they are saying, “We’re here, we’re ready to do the job, and we’ll be able to do it for years to come.” For the final but very important step to closure, documenting a discrete-wiring arrangement that uses this basic connector is straightforward compared to one with more-complex connectors; I began with an annotated photo overview to provide context and a frame of reference, in addition to standard wiring schematic and assembly drawings (Figure 4).

wiring diagramFigure 4 Documentation begins with an annotated photo of the fuses, control relays, and associated terminal strips, to provide overall guidance to the next person as to what’s what and where. Source: author

In the end, I was satisfied that I did not leave an undecipherable wiring mess for the “next fellow” dealing with the thermostat zone wiring, however and whenever that may happen. In years to come, no one will be cursing the anonymous jerk (me) who did such a sloppy job, and while there may be complaints about the hodge-podge of different wire types and colors associated with each thermostat loop coming down to the re-done control panel, well, replacing those runs is outside the scope of my volunteer effort (plus, pulling new wires from upper floors to the basement does bring some risks, so it may be better to leave it in place and learn to live with it!).

Have you ever had to rip out and rewire a messy job that had built up incrementally? Have you ever resorted to low-tech spade lugs and screw terminals, or similar, to solve the problem even though they may seem inelegant? Have you ever said “no problem, I’ll fix and document it later” but that later never came?

References

  1. Crimped Terminations Spade Lug Terminals,” NASA
  2. Know About Spade Lugs Terminals And Ring Terminals,” K.C. Electronic Distributors
  3. Screw terminal,” Wikipedia

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