Z-wave smart plug that can measure power usage of computer equipment?


Does anyone have any recommendations for a Z-wave smart plug that I can use to meter energy usage of several pieces of computer equipment that are plugged into a UPS (120 VAC)? I’ve been using a Zooz ZEN15, but the results were wrong (kWh used was about 80-100x the integral of watts) and their tech support said that multi-computer loads were not supported by that device….



Is your setup: Wall Outlet → Zen15 → UPS → Several computers? If so, it seems like that would always be difficult to determine the usage of each computer.

So would Wall Outlet → UPS → Zen15 → Computer work better? With multiple Zen15 (or equivalent) for the multiple computers if that’s what you need?


I don’t need (or want) to split out individual computers… I’m just trying to measure to total for “all that computer stuff in that room.” (It’s a rack with some switchgear and a couple of raspberry PIs, etc.) But apparently having multiple downstream devices can confuse the metrology components and cause them to ready orders of magnitude off…


Are you on the latest firmware 2.10.0 for ZEN15?
Also be careful because there are two versions of the ZEN15, the new one which uses is the ZEN15 800LR is rock solid. I recall reading that the old ZEN15 shouldn’t be upgraded to the new firmware as it causes issues.

I really hate when companies use the same model number for different iterations of a device.

This is a ZEN15 800LR.

The kWh consumed differs wildly from the integral of watts. I wrote Zooz tech support and they said that the Zen15 can be confused or damaged by multiple downstream devices… “Multiple inductive loads with their rapid current changes happening at once, may damage the device or cause abnormal behavior”. So I’m looking for a suitable device to replace them with.

Interesting. I’m surprised a few raspberry pi and network gear can have such an effect on this device.

That being said, I also went looking for a “heavy duty” power plug with energy monitoring for my home server and ZEN15 was the only thing that ticked all the boxes. Every other plug seemed “lower tier.”

Out of curiosity, what is your average watts?

I was monitoring a rack with a load of only 200W +/- 20. My Zen15 failed, so I tried it on another appliance (a dehumidifier averaging 500W when running), where it also generated spurious kWh readings (though plausible W readings). (FWIW a different Zen15 that had not been used on the server rack reported reasonable stats on the same dehumidifier.)

Zooz tech support was helpful but said that it wasn’t supposed to be used on the first (server rack) load… so I’m trying to find something appropriate…

Does your UPS provide a data port such that you can connect it to an RPi and run a NUT server? I do that with my rack UPS and I get both real time load in watts and percent of capacity which I can then use the Powercalc integration to calculate kWh and other tracking. Otherwise, if you only want a z wave solution, I use Aeotec Smart Switch 6 and 7 and they provide pretty accurate readings of V, A, W, and kWh with multiple loads attached. A few of mine monitor loads that vary time to time ranging from 250W up to 500W. the load type or quantity shouldn’t matter to the plug, it’s just totaling the current flow through the plug.

I don’t believe the manufacturer that they are claiming the multiple downstream devices damaged the power meter functionality. I could see sudden spikes or inrush current can skew or temporarily affect readings, but for the meter to become faulty because of little spikes is rare.

Couple of different solutions that I use.

Some of my loads are constant. For example, small UPS powering POE switch, NAS, pfsense appliance, router. I used a kill-a-watt meter to figure out the average wattage, then use a reimann sum and utility meter to calc the rest in HA. This also removes the need for a smart switch (those switches fail eventually and I don’t want my IT stuff going off line.

If the wattage report looks fine from the current switch use that instead. Use a reiman and utility meter.

I’ve had good luck with Aoetec Smart Switches. I use these on cable modem and router with no problems. I don’t use the kWh reading as I use the watts instead. I have them there since sometime after a power outage the cable modem needs a power cycle, and the router VPN has a bug. So I have HA power cycle those when that occurs.

@squirtbrnr the UPS is this one. I have not tried out its Ethernet or usb interfaces, so I don’t really know what they are or aren’t capable of…

You should be able to plug that into any computer or RPi with a USB-A to B cable. If you configure a NUT server you can then view what information it provides. At the bare minimum it should supply your percent load. The VA (Watts) is already known based on the size of the UPS. Simple math just multiply your load by your total VA and time and you have basic kWh feedback. It’s not entirely accurate but it’s better than an incorrect smart plug. Some of the better UPS units provide realtime Watts usage which you can plug into a Riemann sum.

If you’re not stuck on using a Z-wave plug, I have good results with the WiFi TP-Link KP115 smart plug.
UPS plugs into KP115. PC, speakers, 3 monitors, and some misc stuff plugged into the UPS.

For my network rack I do what @squirtbrnr suggested - NUT sending me data from the UPS. It’s not particularly precise, but it’s good enough.

If you trust the ZEN15’s wattage reading, you might want to try letting HA perform the integral on the measurement to come up with a second opinion on the kWh calculation.

You can do the same with NUT by converting the percent load to (approximate) watts and integrating to kWh. It would be interesting to compare the two values over the course of several days. At a minimum you might learn how efficiently (or not) your UPS performs.

I too am dubious of support’s response about the ZEN15. I’d expect AVR (power filtering) circuitry on your UPS to somewhat “trick” the plug into seeing multiple devices as a single load. On the other hand, the filtering circuitry, or maybe the reactive power component of the UPS, could be what’s messing the calculation. I use the ZEN15 on a switched DC battery charger and find the kWh to be very accurate — the battery finishes charging precisely when I expect based on the kWh capacity/used.

Thanks! (Yes, I have been comparing the Zen15’s kWh reading to an integration template that I created for its W reading. But my concern is that if that plug is not supposed to be used with that load, then what else might go wrong?)

Regarding NUT, this is new to me, but sounds interesting. Is it relatively easy to use NUT to act as a sensor in HA?

Configure the NUT server on the RPi, add the NUT integration in HA, point the configuration to your server.

There’s plenty of documentation available on the internet on how to configure NUT on an RPi. The HA side of things is pretty simple and gives you the sensors once everything is configured correctly.


@squirtbrnr Thanks again, and one other question: I have 4 different UPSs in different rooms. It looks like a single RPi can manage multiple UPSs in NUT, but I think the UPSs need to be connected via USB and I do not have USB wiring between the different rooms (or even extra Cat6 cabling that could be used as a dedicated line for a USB->Cat6->USB converter, unless it ran over IP not just Cat6…). Are there any better options for integrating than running one RPi per UPS?


I don’t know of any other way. Instead of running long cables or USB over IP, I would just put a RPi0W on each UPS and be done with it.

Got it. Great suggestion on going with the the Pi Zero instead, as this is a pretty low-compute-intensity application! Thanks!