Running two base units in medium-sized home?

Hi all,

I’m excited to have discovered IoTaWatt and am seriously considering jumping in. My medium-sized US home has a 200a service with 25 circuits running throughout the house. It makes sense to me to monitor them individually (more data = better, right?) so I’m looking at buying two base units to accommodate as many CT’s as possible.

My question is: I see almost nobody on the forums doing more than one base unit, so I just wanted a sanity check. It seems most people here are content to just monitor the mains, plus put CTs on a few major circuits, double up if they need to, and leave the difference as “unknown / baseline”. Am I a real outlier for wanting data on each circuit? Is it hard to fit that many CT’s in a standard panel box?

To that end, I’ve put together a shopping cart that includes:

  • 2x base units
  • 2x USB power supplies
  • 2x AC reference transformers
  • 2x 200A CT’s (assuming I can split their signals into the other base unit)
  • 24x 50A CT’s

Subtotal: $477.75

And I’d buy one large wall mount enclosure to house it all in.

My plan would be for both units to write data to influxdb so that I could see a UI with combined data in Grafana / Home Assistant.

Photos in case they are helpful:


Allen, I was in the same boat when I first started and I will say that your setup and shopping list looks good to me. If you want to collect everything, I would say go for it, and you will not find a better and well supported product than this one for that job.

I’m a data guy myself and to me more data is always better. :slight_smile: What makes things a bit more difficult is knowing or caring what might be on some of the 120v branch outlet/lighting circuits. I have many of my circuits in an older home that are for things like upstairs outlets or general lighting, but over time other type of things were connected to these circuits as well; ceiling fans. It would be nice if one circuit was dedicated to a room in the home, etc. Again, my being in an older home maybe they do break things up better in a newer install (your panel looks too clean and I would assume newer home).

As you begin to monitor your circuits, you will notice many of your low load one are quite static or not heavy energy usage, so when you compare them to the mains they are really quite small. Things like lights, plugs, bathroom fans, and the like can be quite boring to map over long periods. Things get a bit more interesting when you can see heavy load circuits and the amount of energy they use. Pumps, motors, heating elements and the like (240v circuits) are quite interesting when compared to your overall energy usage. If you have a single IoTaWatt and have to be selective, this is where it makes sense to monitor the heavy load items which can more easily be determined and controlled from the smaller ones. I used to monitor my boiler (240v load) but it is an oil burner which uses electricity to start but once running, there is no energy being drawn. So, I could see it start when the heat or hot water went on, bit again this seemed rather static over time.

For me, the important data, which has changed a bit from then to now, has been the mains, my solar, and I also have a solar battery. I want to make sure I know what I generate with my panels, export/import from the grid, export/import from the battery and the other high load circuits which may impact these three key figures. In the summer I like to see my AC usage and if this is drawing from my solar (day) or battery (night) when I might instead turn it off or higher.

For me it is about things like my dryer, well pump, range, two sub-panels, solar, mains, and battery. From these I can often determine other usage in the home. My dish washer and small counter oven are simply on my 120v kitchen circuits, but when I subtract my main loads from my total usage, I can see when these items are on and drawing power. Much like a hairdryer or curling iron, etc.

Not that it would add too much, but also be aware that you will need to have the storage as well for all this data you will collect over time. I would be interested to see what other have to say. I’m just at 1 year with the IoTaWatt and I can say that over that period I have settled in on the Items I’m interested in and have a few open ports in the device, but not sure I really case to collect the data from my smaller circuits.

I would say that @quella did a pretty good job of answering, I will only add two things:

The picture of your panel does not include labels, but I see you have quite a few 240V 20A breakers. That’s usually electric baseboard heat. If so, those can each be monitored with a single 50A CT, or up to three could be combined with a single 50A CT.

The other point I will make about many branch circuits is that LED lighting has been a game changer with respect to power usage. There was a time that a dozen lightbulbs would be on using close to 1,000 Watts. Now that’s 100 Watts. So what used to be a big part of the total load is gone now. When these circuits are combined, they have a very low baseline and any transient loads like hairdryers are easy to pick out, and don’t amount to anything in the big picture anyway.

I’m going to address the sizing of the CTs in the other post about that this morning.

I have two IoTaWatt units. I started with one. Previously, I had a single ecm-1240 (from Brultech, has 7 inputs).

Monitoring just the mains will provide an abundance of data, but it is harder to make sense of it and do something about it. If you are interested in learning more about utilization monitoring every circuit will provide you with lots of data, but most of it will be really boring and not very valuable.

Finding out your base load (the minimum power used, ie stuff that is on 24hr/day) and figuring out how to reduce it, is one thing that you can do with only the mains monitored. But, having more circuits monitored makes it easier.

Influx doesn’t do math across streams (but the new stuff still in beta might make this possible) so you have to do that before it gets there. I use NodeRed for some things (like the efficiency of my dehumidifier).

Anyway, I think having two is better, but the math is harder. One is probably going to get more than enough data to keep you busy for some time.

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Thanks everyone for your helpful replies! I spent most of yesterday with a friend testing each outlet / switch to see which circuits are which, and I think I’ve decided that yeah for the extra cost of another unit I’d enjoy having more data.

In case anyone is curious, the house is from 1899, with a mix of knob & tube wiring, 1970’s era cloth ungrounded 2-wire, and a little bit of modern romex. I spent yesterday with the electrician checking each outlet and our plan is now to pull a lot of fresh circuits to modernize as much of the house as possible. While he’s at it I’ll have him setup the IoTaWatt :slight_smile:

To minimize the footprint of the box, I’m considering ‘stacking’ the two base units on top of each other inside the box. If I need to access the rear one for some reason I can always temporarily disconnect the CT plugs and remove the front one. Is that a problem for any other reason, like ventilation?

Thanks again!

I like the stack idea. Maybe consider using two threaded posts so that the upper unit has a nut on each side of the mounting flange. Be sure to post pics when done.

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Hey Allen,
I see I’m a little late to the party but wondered how things were going for you. I’m running two base units as well but my setup differs from yours somewhat. My home was built in 1976. It’s been remodeled and added on to once since then. I have a 100 amp panel that feeds the original part of the house and a 200 amp panel in the basement that feeds the new addition. Plus I have a 30 amp panel that feeds the garage. All of these panels are fed from an external disconnect panel that’s outside next to my meter.
The eternal disconnect panel and meter are directly outside from the 100 amp panel but the 200 amp panel is all the way on the other end of the house. I started out with a single unit on the 200 amp panel mostly because that’s where all my big usage is. I was able to deduct the other panels usage by subtracting total power on the 200 amp panel from the overall usage figured from taking meter readings (sometimes hourly and daily). This got to be a pain so I purchased a second base unit and ran some conduit in from the external disconnect panel. Then I could see everything which made things much easier. I didn’t put CT’s on the mains though. I put them on the mains to each panel and let the iotawatt add them up for total power consumption. So I have a main 1A and 1B for the 100 amp panel and a main 2A and 2B for the 200 amp panel plus G1 and G2 for the garage feeds. The 200 amp panel at the other end of the house has its own base unit but it only measures individual circuits.
Quella pretty much nailed it with his response in that there are a lot of circuits that are pretty boring to monitor. I started out with a single base unit and a few CT’s and just moved the CT’s around for a few months trying to decide what I wanted to watch. I’m like you in that more is better. My sump pumps, deep freeze, geothermal, well pump and water heater are all on the 200 amp panel so I kind of had to have something more than overall usage monitoring for that panel. I’ll have to say that knowledge is power. I’ve been able to reduce my daily consumption by almost 10 kw/hrs.
It would be nice if the base units could share info with each other. They’re on the same wifi network. It would also be nice if there was a temperature probe that could be installed in one of the feeds. I’d like to compare heating and cooling consumption against outdoor temperature on the same graph. I’d also like to be able to put both base units on the same graph. I guess I could buy two more CT’s and use them to monitor the mains at the 200 amp panel so total power at that panel is shown on that base unit but I already monitor that on the first base unit at the other end of the house. Anyway, I saw you were searching for others with multiple base units and thought I’d share my setup in case someone had the same questions in the future. The addition of the iotawatt units to my house have been a game changer for me and I cannot recommend them enough to anyone I talk to.
The only trouble I’ve had so far is the iotawatt total power consumption doesn’t match the meter. Not sure how much disparity is considered normal but mine is currently 8 kWh less than the meter and it’s only the 12th of the month. The difference grows each day so it’s not an issue of when the meter gets read. I have a smart meter so I take whatever the electric company says the meter read at the beginning of the month and use that number for reference. I understand there could be flaws in this method but the iota and the meter are usually right on at the beginning of the month and slowly get farther apart as the month progresses. The meter always shows more usage than the iota does. I’m wondering if it’s a calculation thing with the iota since I’m adding 6 points together for total power consumption. I’ve considered moving a couple CT’s directly to mains from the meter to see if anything changes. All of my total power is measured on one iotawatt base unit so it’s not an issue of me trying to add two base units together. It’s not a huge deal but it’s worth mentioning. I’ve checked and double checked the CT’s for good connection. Anyway, hope you’re liking your 2 units and would like to hear how things are going. Thanks, Jason

Hi Jason,
Just wanted to weigh in on your mains reconciliation issues and get some context on that 8kWh. Your sum total of six individual IoTaWatt mains feeds is 8kWh low of the meter reading after 12 days. So that’s .67 kWh/day low. If you average 67 kWh/day, that would be 1%. If you average 33kWh/day that would be 2%. Can you shed some light on your average daily usage to put this in perspective?

I’m also curious to know if you have been able to check the voltage calibration of the VT where the mains CTs are.

I have not checked the accuracy of the VT against my multimeter but it’s very close to voltage readings I’ve had when performing electrical work in the house. I’ll definitely check the VT against my multimeter soon. I hadn’t thought of that. Also, my electric consumption is around 30 kWh’s per day for this time of year. I have not done any daily testing to see how it does on a 50 kwh day versus a 20 kwh day. My dryer is electric and pulls around 6000 watts when running. It would have an inrush draw when starting that the iota might not see as well as the meter. My geothermal uses about 3000 watts when running and would be the same plus it runs and cycles considerably more than the dryer. Also, this is only my first full month of data collected from the mains. I installed the second iota on February 6th but I’ve used the graphing function to monitor selected dates in February and it’s pretty consistently reporting less than what the meter shows. I’ll check the VT against the multimeter and the iota status page in real time when I get a chance and see what I find. I should also add that voltage at my house runs around 124 to 126 and is usually in the 125 range all the time.

Any significant inrush may not appear on the graph because it is at best 5 second averages, but the averages are roughly 500ms samples, so significant inrush is in there. Also, the total power consumed by inrush delta would be third order in this discussion.


So difference is around 2%. That could be voltage calibration, or a CT that isn’t seated well and/or part of it can be the calibration of the meter. The goal would be to get that number to 1%.

I checked the voltage and found the VT to be reading exactly one volt higher than what my multimeter read. I adjusted the VT using the calibration setting in the configuration page. My meter is a craftsman digital model 82141. I can borrow a fluke but it might be few days. The outlet my VT is plugged in to is less than 5 feet away from the panel and is a single outlet circuit that once fed a deep freeze. I didn’t want to unplug anything so I pulled the panel cover and tested voltage on the circuit at that end. I know voltage could possibly be lower at the outlet but that outlet and circuit only powers the iotawatt so I’m guessing any voltage drop in the 5 feet of wire from the panel to the outlet is very very minimal. I turned on some lights while I had my meter hooked up and the iotawatt seemed to track voltage changes within one tenth of what the meter was reading in real time. It should be said that I didn’t perform this calibration step when I originally set this iotawatt up. I just went with what it read because it seemed pretty close to what I’d found. The calibration factor was reduced from 10.79 to 10.71 to get voltages identical. I originally didn’t want to calibrate off my craftsman meter and planned on using a fluke but never got around to doing it. So this is the first and only time the iotawatt VT has been compared to a multimeter.

Well, since you report the IoTaWatt reading fewer kWh than the meter, this will not improve the situation as lower voltage will mean lower power from the IoTaWatt. You might want to look at a graph of each mains pair when a 240V load switches on to see if both CTs indicate the same increase.

They do not! I just checked my geothermal. It’s a pure 240 v load in that it does not possess a neutral. The CT for it is doubled but main 2A shows less watts than main 2B when it’s running. Also main 2A shows a spike at startup that main 2B does not. The mains are measured on one iotawatt unit while the geothermal circuit is monitored on the other iotawatt unit. I have them labeled iota 1 and iota 2. #1 measures the mains and #2 is on the 200 amp panel at the other end of the house. The VT on the #2 unit has never been calibrated as well.

Those 200A CTs have paper between the core surfaces to protect them against chipping and corrosion until installation. They usually just fall out when you open them, but one could still be in there, or the surface could just have some impurity. Sometimes they just are not closed securely. It would be worth checking that mains CT.

Might be on to something. I checked the mains CT’s. No paper. I wiped off the connecting surfaces but they didn’t appear dirty. I clamped them back on and made sure they were seated well. I had my iPad out there with me so I could see the iotawatt readings while I was working. Main 2B appeared to be reading higher before I messed with it. I came inside and powered everything else off in the 200 amp panel except the geothermal then raised the thermostat to kick it on. Now both mains read identical when it’s running.

I looked back thru historic data and found there were times when the mains were identical when the geo was running. Of course, there are other loads on the panel at all times so the only true test is with everything else powered off. There are no 240v loads on any of the other panels. The only thing different than normal is in the 100 amp panel. The original part of the house was wired with a lot of multi-wire branch circuits. It looks like 12/3 was used on circuits and the black wire would feed one bedroom and the red wire would feed another bedroom and both bedrooms would share the neutral. The black and the red each had their own separate 20 amp breaker. When I remodeled, I eliminated all but one of these as it was extremely difficult to replace the feed to the upstairs. What I did instead was put a two pole 20 amp breaker in to feed the two separate circuits thinking if any maintenance needed done, the only way to shut off power would be to shut off power to both the red and black to prevent any power from getting into the other circuit thru the neutral. What I didn’t check before redoing the electrical was to see if the black and red wires were fed from the same leg or not. Using a double pole breaker means they are fed from opposite phases. Wasn’t sure if it mattered but that condition exists in the 100 amp panel.

That’s completely copacetic. But only when the two hot leads are opposite legs. When that is the case, the neutral only carries the difference between the two hot conductors.

If they are the same leg, the neutral would be subject to the combined Amps of the two hot leads. So if 20A breakers, the neutral could be subjected to 40A with only 12ga wire. That would require functioning smoke alarms.

Yes. I knew by using a double pole breaker, the neutral would only carry the difference between the black and red. Also, it limits overall current to 20 amps instead of 20 amps per leg. I figured it was probably done correctly before I messed with it but I didn’t verify that before I replaced the panel. The circuits in question are bedrooms and a bathroom. The black feeds two bedrooms and the red feeds one bedroom and one bathroom. The bedrooms draw very little but have entertainment centers so it’s helpful to see phantom load and what time the kids actually turn stuff off and go to bed. The bathroom has curling irons and hair dryers for its big usage but those are usually pretty short term. I’ll continue to monitor power consumption relative to the meter and keep you posted. I agree that adjusting voltage down only makes the problem worse. I checked all the main CTs today and all appear to ok. If I’m 8 kWh off now, it stands to reason I’ll be around 18 kWh off by the end of the month. Maybe more now that the voltage has been adjusted. I’ll borrow a fluke tomorrow and check voltage again over the weekend

18 kWh a month is 218 kWh a year. Last year, I used a total of 15,200 kWh or about 1266 kWh per month and 41 kWh per day. I’m off to much better start this year. If I can maintain my current pace, I’ll reduce my annual consumption by close to 4000 kWh. My biggest changes so far have been smart power strips for entertainment centers, putting a timer on my dehumidifier, and changing the anticipation settings on the geothermal. A gas dryer would be asignificant reduction in electrical use but might not actually reduce my overall energy use. LP is currently considerably cheaper than electricity in my area. My electric meter was one of the first smart meters installed in my area so who knows, maybe the meter is off but I doubt it. Anyway, even if the iotawatt is off a little, it’s still the single most helpful tool I’ve purchased in a long time. It will pay for itself for sure.

Checked voltage with a fluke - the iotawatt was low. The original calibration factor was 10.79. I checked with my craftsman meter and found the iotawatt was reading high so I adjusted calibration factor down to 10.71. Tonight I checked with a fluke and the iotawatt was reading considerably low. The the calibration factor is now 10.81. Two tenths higher than where I started. I went ahead and calibrated my second base unit while I had the fluke and it needed adjusted to 10.81 as well. I took a meter reading so I’ll see how it does.

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