Morphing from power strips to PDUs

Article By : Bill Schweber

The ubiquitous consumer power strip may soon be replaced at home by a more advanced power distribution unit due to its benefits for the smarter home.

You undoubtedly have lots of basic power strips, those six-position AC-outlet expanders sold just about everywhere from under $10 to around $25 (Figure 1). They all supposedly meet regulatory safety standards according to their stickers (and those couldn’t be fake, of course), but certainly their ruggedness and quality varies. Some come without switches, some have more spacing between outlets to provide room for AC/DC adaptor bodies, some have individually switched outlets, and some even claim to have some level of surge and transient protection (that’s another mystery feature, in reality).

Figure 1 The basic, inexpensive six-outlet power strip comes in countless variations and sizes, and with varying quality. (Source: Excitron)

I only buy those with an illuminated on/off switch, which makes it easy to confirm, with a glance, that the strip is powered which avoids wasting time looking for an obvious “no power” problem. Some older ones I have from years ago even have convenient mounting ears so they could be easily mounted to a wall or board, but newer ones do not. I read somewhere (don’t recall where) the “ears” were taken away due to the strips’ definition as “temporary” units by UL and others, while ones with ears might be attached “permanently” which they shouldn’t be. Instead you have to resort to using the four little slotted-screw holes on their back which are trickier to match; it takes an accurate template to gauge their position, and then you need screws with heads and bodies that fit the key slots “just right.”

Due to regulatory constraints, a standard 15-A power strip is limited to six outlets, although there are some ways to get around this restriction. I got tired of the power-strip jungle I had grown, and when I found a nice piece of Plexiglas about 12×18 inches (30×47 cm), I bought four identical strips, mounted them tightly from the back with #6 machine screws and nuts, and so made my own AC-distribution center (Figure 2). While I did lose one outlet per strip due to the daisy-chain (except for the last one) it has still been a very effective arrangement despite its appearance. (For the quantitative among you, the number of available outlets is [6 + ((n-1) x 5)] for n power strips). Total current is well under 15 A since many of the loads are small.

Figure 2 You can never have enough outlets, as this daisy-chain arrangement of board-mounted power strips shows. (Source: author)

But even the basic power strip is seeing major enhancements and becoming a smarter PDU – power distribution unit. As expected, these PDUs first appeared at installations where performance and useful features are vital and their higher up-front cost is easily justified by the longer-term benefits, such as data center racks. These PDUs have different levels of functionality. The website of major PDU (and other product) vendor Tripp Lite clearly explains the various PDU levels: there’s the basic PDU (Figure 3), which is a much-better version of the cheap power strip but with 13 outlets (it’s fed by a higher amperage line, so that’s OK).

Figure 3 This rack-mount basic commercial PDU with 13 outlets is rated to 1.8 kW and would avoid the daisy chaining between multiple six-outlet strips. (Source: Tripp Lite Inc)

But don’t stop there, when you can move up to these PDUs:

  • The metered PDU, which can locally monitor load level and avoid potential overloads with a built-in digital current meter
  • The monitored PDU, similar to a metered PDU, but can remotely monitor single- or three-phase voltage, frequency, and load levels in real-time via a built-in network connection
  • The switched PDU provides the ability to remotely monitor, connect or disconnect loads; it can locally monitor load level via its digital current meter, and remotely control individual outlets for the rebooting of locked equipment (very nice feature), for custom power-on/power-off sequences, and even load-shedding of non-essential loads during blackouts to extend backup runtime. The web/network interface reports detailed voltage, amperage, and kilowatt output values per breaker bank and there is even optional sensor-based temperature and humidity data

At first, the smart switched PDU seems like too much of a good thing for the average user. But with the proliferation of smart homes, smart and controllable PDUs make sense. You may want to monitor the AC line outlets via a smart app, and perhaps remotely execute a power down/up reboot if things aren’t right. Given the reality that products with advanced functions and features are first seen at higher-end installations but soon migrate down to the mass market, I wouldn’t be surprised to see more of these in a package and price for the home and receiving widespread adoption.

Would you like a smart PDU for home use? Or is yet another complication to the smart home that will only add to the number of things which have to be initialized, documented, and maintained or perhaps cause the system to crash? What about a hacker controlling the power to your home’s smart functions?

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.

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