Just give me a decent data sheet, please

Article By : Bill Schweber

How could vendors of AC power strips not call out the critical outlet-spacing dimension, especially when they tout their strip’s ability to handle AC adapters without adjacent physical interference?

As someone who has dealt with a lot of analog components, I now realize I’m spoiled. How so? Even the most-basic analog component from a reputable vendor comes with a detailed data sheet. This documentation includes numerous graphs, charts, and tables defining component performance under a wide variety of conditions and categorizing operation from many perspectives with respect to parameters such as temperature, supply voltage, load conditions, and more. A good analog (or any) data sheet pushes the marketing accolades to the background and “opens the kimono” on reality.

Even the humble, ubiquitous op amp has a data sheet which tells you, in most cases, just about everything you need to know. While there may be gaps, these are either unusual or truly subtle specs you are looking to nail down. A good data sheet goes beyond “typical” numbers and gives maximum and minimum numbers as needed. When that’s not feasible, some have probability distributions for key specifications showing, for example, that 80% of the units will be within certain bounds.

Consider this: the general-purpose AD817 from Analog Devices (a high-speed, low-power, wide supply-range amplifier) comes with a 12-page data sheet with dozens of graphs. I’ve seen op amp data sheets running 30 and more pages. Or look at the Texas Instruments SN74LVC1G66 (a 5-V, 1:1 SPST, one-channel analog switch): its data sheet runs 39 pages. We expect data sheets to include electrical, mechanical, packaging, layout, handling, and soldering details so you can model and design with the part before spending valuable time trying it live, to have some basic confidence that it will work and also fit. Sure, sometimes a component doesn’t meet a promised spec on the data sheet, but that’s not a common situation at all among top-tier vendors.

Unfortunately, vendors of basic “simple” products seem to think that data-sheet details aren’t needed. This really hit me when I took some preliminary steps to clean up the three-zone wiring I had helped a friend install for his HVAC system (see Related Content at the end). The resultant wiring, shown in Figure 1, is a rat’s nest that is unprofessional, embarrassing, untraceable, nearly impossible to debug, perhaps unreliable, and reflects badly on me and our profession.

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Figure 1 This layered mess is the result of installing three smart thermostats each a year apart – the wiring got worse incrementally.

While the rewiring will of course have to wait until heating season is over, I figured I could at least start planning it now. Each zone of the system has its own 120V/24V AC transformer. (Yes, a single transformer could easily handle the very modest current needs of all three loops, but right now I am doing wiring clean up; plus, there’s something reassuring about having an independent power source for each zone.) I figured the first and easiest place to start would be to replace the nearby kludgy power-strip arrangement, shown in Figure 2, using a wall-mounted outlet box plus a single strip.

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Figure 2 The three AC transformers (24 V) are also mounted in a haphazard, unsightly manner.

The obvious way to make this replacement is to use a power strip running horizontally, as shown in Figure 3, with the outlets at right angles to the strip so the outputs of the transformers – which look like “wall warts” – hang down.

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Figure 3 The plan was to start by getting a power strip with the right outlet orientation and spacing to clean up the triple-transformer arrangement.

Because the transformers are about 2.25 inches (5.6 cm) wide, I realized that the spacing between adjacent (or alternate outlets) needed to be at least that wide. No problem, I thought; I’ll go on the web, find lots of power strips, and pick one out with the needed orientation and with a center-to-center (CTC) spacing that’s wide enough. Even if “tight,” I figured it would work out OK if I just used outlets 1, 3, and 5 of a six-outlet strip as long as that spacing exceeded the transformer.

That’s when my “spoiled by good data sheets” reality hit. Long story short: only one of the strips I looked at on Amazon that might work (Figure 4) gave out the critical dimension of distance between outlets. They all extolled their overall size, line cord length, current rating, surge protection, wire gauge, and other interesting points, but only one gave the simple linear dimension I needed. Some claimed to have extra spacing for wide power units (but gave no dimensions) or had vague statements such as “more spacing than standard strips,” which wasn’t helpful. Others had one outlet off to the side for a single wall wart, but the other outlets were too close. (Note that I was looking for was a basic $20-$30 power strip, not an extra-long, $80-$100 industrial one.)

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Figure 4 These are just a few of the AC power strips I looked at to gauge CTC spacing. Only one (upper right) showed the needed CTC dimension while one (bottom middle) had a center-to-nearby slot dimension.

Other outlets gave some dimensions, but not the CTC one I needed. I even tried to go directly to the web sites of the power-strip vendors, but the vendors either didn’t have their own site or they just linked back to Amazon. Not only was this frustrating, but I knew that somewhere in their production system they must have the drawing I needed, so they could establish their tooling to punch the sheet metal or mold the plastic of the power strip body.

In the end, I reverted to a quaint, old-fashioned method of determining the CTC number I needed. I pulled out my digital caliper (the best thing ever), dividers, and a calculator, Figure 5, and gauged the CTC distance between adjacent and alternate outlets. I used the known actual distance between socket blade openings (15 mm) versus that dimension on the screen, then used basic proportional math to scale the CTC distance I also measured on screen.

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Figure 5 By reverting to basic tools — a digital caliper, dividers, and a calculator — I was able to measure the on-screen CTC parameter and relate it to known dimensions.

Basic tools plus simple algebra gave me the answers I needed in my quest for this obvious specification. In case you’re curious, the “winner” of my analysis was the JiangMaster six-outlet power strip sold via Amazon, bottom right of Figure 4, which I measured as having a CTC distance of three inches (7.8 cm) between alternate outlets. This easily exceeded my 2.25-inch clearance requirement, while leaving some airflow space between units — always a good thing.

Have you ever experienced what you thought was an obvious specification that should have been called out, but wasn’t? How did you resolve its absence? Did you get a unit and measure what you needed? Did you get an answer from the vendor? Was this answer in writing or was it just a verbal assurance?

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